Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla

 
Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
Conservation and
       Management of
        North American
            Bumble Bees

                             By

       Dale F. Schweitzer, Nicole A. Capuano,
        Bruce E. Young, and Sheila R. Colla

A product of the USDA Forest Service and NatureServe
  with funding from the National Fish and Wildlife Foundation
Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
Executive
                                                                                                                                Summary
                                                                                                                                This document provides a brief over-      Management recommendations center on providing suitable nesting and foraging
                                                                                                                                view of the diversity, natural history,   habitat in close proximity during the annual period of bumble bee activity. The major
                                                                                                                                conservation status, and manage-          recommendations are:
                                                                                                                                ment of North American bumble             Minimize exposure to pesticides.
                                                                                                                                bees, genus Bombus. The spring to         • Avoid spraying while a crop is in bloom.
                                                                                                                                late summer period of colony found-       • When spraying is necessary, do so under conditions that promote rapid breakdown
                                                                                                                                                                             of toxins and avoid drift.
                                                                                                                                ing, build up, and production of          • Provide habitat for nesting and overwintering sites.
                                                                                                                                reproductive individuals, followed        • Leave unplowed, undisturbed areas with logs and clumps of grass where bumble
  This version corrects an error in Figure 1 that appears in the print version. Nunavut has been distinguished from             by the overwintering of new queens           bees can find nesting and overwintering sites.
  Northwest Territories and the geographic projection has been changed to better depict northern North America.                 provide the natural history basis for     • When nesting sites are limited, consider providing artificial nest boxes.
                                                                                                                                                                          • Assure continuity of nectar and pollen resources when bumble bees are active from
                                                                                                                                management considerations of the             spring to late summer.
                                                                                                                                approximately 46 North American           • Increase abundance and diversity of wild flowers, suitable garden flowers, crops,
                                                                                                                                species. Most bumble bee species are         and even weeds to improve bee density and diversity.
                                                                                                                                                                          • Mow when bumble bees are dormant, if possible.
                                                                                                                                currently not threatened or docu-
                                                                                                                                                                          • When summer mowing is necessary, stagger fields to ensure that some flowers are
                                                                                                                                mented as declining except in areas          always available.
                                                                                                                                of intensive agriculture. Eight spe-      • Time prescribed burns as recommended for mowing.
                                                                                                                                cies from three subgenera, however,       • Ensure that nesting habitat is in close proximity (500-800 m; 0.3-0.5 mi) to foraging
                                                                                                                                                                             habitat.
                                                                                                                                have declined drastically during the
                                                                                                                                                                          • Encourage agricultural authorities to place tight restrictions on the use of bumble
                                                                                                                                last 15-20 years. These include three        bees for crop pollination to prevent the spread of diseases.
                                                                                                                                species that are obligate parasites
                                                                                                                                                                          After reviewing the literature on bumble bee conservation and management, a number
                                                                                                                                on other declining species. The            of gaps in our knowledge about bumble bee biology become apparent. These gaps, listed
                                         Report coordination by Pollinator Partnership                                          pathogen spillover hypothesis, which       here to stimulate research in different regions of North America, include:
                                                 Designer: Marguerite Meyer                                                                                               • How are bumble bee populations changing over time?
                                                                                                                                proposes that diseases from infected
                                                                                                                                                                          • How important are forested habitats for bumble bee diversity?
                                                                                                                                commercial colonies imported from         • What habitats do bumble bees use for overwintering?
                                                                                                                                Europe are infecting native popula-       • How do habitats, including human-altered ones, vary in quality for bumble bees?
                                          Dale F. Schweitzer1, Nicole A. Capuano1,                                              tions of closely related species, may     • Do areas where severely declining species remain share common habitat or climatic
                                           Bruce E. Young1, and Sheila R. Colla2                                                explain the sharp declines of most             features?
                                                                                                                                                                          • What are the foraging needs and diet breadth of bumble bee species?
                                                                                                                                species. Other threats to bumble
                            1
                             NatureServe, 4600 North Fiarfax Dr., Floor 7, Arlington, VA 22203                                                                            • How are bumble bees affected by fire and fire management?
                                                                                                                                bees include climate change, loss of      • How do toxins affect bumble bees differently from honey bees?
                                2
                                 Biology Department, York University, Toronto, ON, Canada
                                                                                                                                nesting and foraging habitats and         • How broad is the threat of diseases from non-native bees spilling over to native
                                                                                                                                pesticide use.                                 bumble bees?
Cite this document as: Schweitzer, D.F., N.A. Capuano, B.E. Young, and S.R. Colla. 2012. Conservation and management of North
            American bumble bees. NatureServe, Arlington, Virginia, and USDA Forest Service, Washington, D.C.

                                Conser vation and Management of North American Bumble Bees                                                                                 NatureServe and the U.S. Forest Service                                                3
Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
Executive
                                                                                                                                Summary
                                                                                                                                This document provides a brief over-      Management recommendations center on providing suitable nesting and foraging
                                                                                                                                view of the diversity, natural history,   habitat in close proximity during the annual period of bumble bee activity. The major
                                                                                                                                conservation status, and manage-          recommendations are:
                                                                                                                                ment of North American bumble             Minimize exposure to pesticides.
                                                                                                                                bees, genus Bombus. The spring to         • Avoid spraying while a crop is in bloom.
                                                                                                                                late summer period of colony found-       • When spraying is necessary, do so under conditions that promote rapid breakdown
                                                                                                                                                                             of toxins and avoid drift.
                                                                                                                                ing, build up, and production of          • Provide habitat for nesting and overwintering sites.
                                                                                                                                reproductive individuals, followed        • Leave unplowed, undisturbed areas with logs and clumps of grass where bumble
                                                                                                                                by the overwintering of new queens           bees can find nesting and overwintering sites.
                                                                                                                                provide the natural history basis for     • When nesting sites are limited, consider providing artificial nest boxes.
                                                                                                                                                                          • Assure continuity of nectar and pollen resources when bumble bees are active from
                                                                                                                                management considerations of the             spring to late summer.
                                                                                                                                approximately 46 North American           • Increase abundance and diversity of wild flowers, suitable garden flowers, crops,
                                                                                                                                species. Most bumble bee species are         and even weeds to improve bee density and diversity.
                                                                                                                                                                          • Mow when bumble bees are dormant, if possible.
                                                                                                                                currently not threatened or docu-
                                                                                                                                                                          • When summer mowing is necessary, stagger fields to ensure that some flowers are
                                                                                                                                mented as declining except in areas          always available.
                                                                                                                                of intensive agriculture. Eight spe-      • Time prescribed burns as recommended for mowing.
                                                                                                                                cies from three subgenera, however,       • Ensure that nesting habitat is in close proximity (500-800 m; 0.3-0.5 mi) to foraging
                                                                                                                                                                             habitat.
                                                                                                                                have declined drastically during the
                                                                                                                                                                          • Encourage agricultural authorities to place tight restrictions on the use of bumble
                                                                                                                                last 15-20 years. These include three        bees for crop pollination to prevent the spread of diseases.
                                                                                                                                species that are obligate parasites
                                                                                                                                                                          After reviewing the literature on bumble bee conservation and management, a number
                                                                                                                                on other declining species. The            of gaps in our knowledge about bumble bee biology become apparent. These gaps, listed
                                         Report coordination by Pollinator Partnership                                          pathogen spillover hypothesis, which       here to stimulate research in different regions of North America, include:
                                                 Designer: Marguerite Meyer                                                                                               • How are bumble bee populations changing over time?
                                                                                                                                proposes that diseases from infected
                                                                                                                                                                          • How important are forested habitats for bumble bee diversity?
                                                                                                                                commercial colonies imported from         • What habitats do bumble bees use for overwintering?
                                                                                                                                Europe are infecting native popula-       • How do habitats, including human-altered ones, vary in quality for bumble bees?
                                          Dale F. Schweitzer1, Nicole A. Capuano1,                                              tions of closely related species, may     • Do areas where severely declining species remain share common habitat or climatic
                                           Bruce E. Young1, and Sheila R. Colla2                                                explain the sharp declines of most             features?
                                                                                                                                                                          • What are the foraging needs and diet breadth of bumble bee species?
                                                                                                                                species. Other threats to bumble
                            1
                             NatureServe, 4600 North Fiarfax Dr., Floor 7, Arlington, VA 22203                                                                            • How are bumble bees affected by fire and fire management?
                                                                                                                                bees include climate change, loss of      • How do toxins affect bumble bees differently from honey bees?
                                2
                                 Biology Department, York University, Toronto, ON, Canada
                                                                                                                                nesting and foraging habitats and         • How broad is the threat of diseases from non-native bees spilling over to native
                                                                                                                                pesticide use.                                 bumble bees?
Cite this document as: Schweitzer, D.F., N.A. Capuano, B.E. Young, and S.R. Colla. 2012. Conservation and management of North
            American bumble bees. NatureServe, Arlington, Virginia, and USDA Forest Service, Washington, D.C.

                                Conser vation and Management of North American Bumble Bees                                                                                 NatureServe and the U.S. Forest Service                                                3
Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
where appropriate. The biblio-    and Europe. As in the rest of the world,           group of North American bumble              varying degrees with body heat to speed growth. This
                                                                                                                                                                                                                                                   Bombus insularis.
                                                       graphic references provide an entry   bumble bee diversity in North America              bees, occurring from subtropical to         adaptation is probably among the reasons why
                                                                                                                                                                                                                                                   Photo James Strange
                                                point into the growing literature on         is lowest in the southern lowlands and             boreal zones.                               bumble bees can thrive in cool conditions. As in
                                              bumble bees. Because scientific papers on      highest in cooler northern and mountain            Subterraneobombus (2 species)—A             all social bees, workers are females. Workers
                                              bumble bees are being published with in-       regions (Figure 1). For example, most              long-tongued, underground-nesting           do not mate, but can reproduce by laying
Introduction                                  creasing frequency (Goulson et al. 2010),      bumble bees in Arizona occur only in the           group primarily occurring in open           unfertilized eggs, producing males. At the
                                              we recognize that this document provides       mountains. This pattern is opposite of             northern and montane areas, such as         end of the colony cycle, queens also lay
Bumble bees are a familiar component of
                                              a snapshot of the state of our current         most plant and vertebrate groups, which            meadows.                                    unfertilized eggs that become males.
our terrestrial fauna. In the past, sight-
                                              knowledge and that subsequent research         generally decrease in diversity with               Thoracobombus (2 species)—A wide-
ing a bumble bee may have elicited no                                                                                                                                                       If nectar and pollen resources are ad-
                                              will fill in some of the knowledge gaps we     latitude.                                          spread group occurring throughout
more than a mental note to avoid getting                                                                                                                                                    equate, the colony will produce males
                                              identify here.                                                                                    the Northern Hemisphere as well as
stung or at most wonderment at how they                                                      In North America, the genus Bombus                                                             and new queens from about June to
can be active on high mountains or in                                                        comprises eight subgenera. These are:              New World tropical mountains. In            October, depending on the species,
cold climates. Today we pay them much         Diversity                                         Alpinobombus (4 species)—Bumble                 North America these species have            latitude and elevation. The males
more attention. Precipitous population                                                           bees of the arctic and high alpine areas.      long tongues and tend to nest above         and queens feed and then mate.
declines have affected several species,       Of the 250 species of bumble bees recog-                                                          ground.                                     In the fall, the new queens locate
                                              nized by taxonomists, approximately 46            Bombias (2 species)—A small group
creating cause for conservation concern.                                                         of bumble bees that occur primarily in                                                     a suitable site to overwinter (for
In addition, the loss of introduced honey     occur in the U.S. and Canada (See Ap-                                                                                                         example, mulch, rotting logs, or
bees (Apis mellifera) in both managed and     pendix for notes on species classification         open grasslands.                            Natural History                                loose soil). The males, workers,
                                              used here). All North American species            Bombus (5 species)—“Typical”
feral colonies has increased the need for                                                                                                    Annual Cycle.— North American                  and old queen all die by the
                                              are native to the continent. Most species          bumble bees that occur in a variety of
native pollinator species. Bumble bees are                                                                                                   bumble bee species vary somewhat in            onset of winter.
                                              have fairly broad ranges either east or            temperate and boreal habitats.
generalist pollinators, performing a key                                                                                                     their natural history. Bumble bees gener-
                                              west of the Rockies or across northern            Cullumanobombus (5 species)—Most-                                                           Foraging and nutrition.—
function in their ecosystems. They also                                                                                                      ally produce one generation per year. In
                                              Canada, although a few such as Bom-                ly bumble bees of high alpine grass-                                                       The workers gather nectar and
form a significant portion of the native                                                                                                     the spring, queens emerge from hiberna-
                                              bus franklini in northern California and           lands and semi-desert.                                                                     pollen to satisfy both their own
insect community that pollinates crops                                                                                                       tion to feed on flower nectar and search
                                              southern Oregon have restricted ranges.           Psithyrus (6 species)—“Cuckoo” bees                                                         nutritional needs and those
worth $3 billion each year in the United                                                                                                     for nest sites, which may be above or
                                              Six species, including three of the four           that parasitize nests of other bumble                                                      of the nest. Adults depend
States (Losey and Vaughan 2006). For                                                                                                         below ground, or either, depending on
                                              North American species in the subgenus             bees.                                                                                      on nectar for carbohydrates
both of these reasons, land managers are                                                                                                     the species (Thorp et al. 1983, Kearns
                                              Alpinobombus extend their ranges to Asia                                                                                                      and gather pollen as a protein
increasingly interested in bumble bee                                                           Pyrobombus (20 species) —The largest         and Thomson 2001, McFrederick and
                                                                                                                                                                                            source for larvae. A queen
conservation and management (Goulson                                                                                                         LeBuhn 2006). Bumble bees frequently
                                                                                                                                                                                            bumble bee forages for nectar
et al. 2010).                                                                                                                                inhabit abandoned rodent nests, probably
                                                                                                                                                                                            when she emerges in the spring,
                                                                                                                                             because these structures insulate the bees
This document summarizes recent                                                                                                                                                             and for another month or more
                                                                                                                                             from cold temperatures. Nests also tend to
information about bumble bee declines                                                                                                                                                       while she alone rears the first
                                                                                                                                             be constructed in areas with south facing
and their management in North America.                                                                                                                                                      brood of workers, during which
                                                                                                                                             exposures. Species nesting above ground
By “bumble bee”, we refer to species of                                                                                                                                                     time she must also collect pollen to
                                                                                                                                             may use long grass or hay stacks. A few
the genus Bombus (Hymenoptera, Api-                                                                                                                                                         feed her young.
                                                                                                                                             species will use tree cavities or bird boxes
dae), including the cuckoo bumble bees
                                                                                                                                             as nest sites. In urban areas, bumble bees     Although some bumble bees can
in the subgenus Psithyrus. We start with
                                                                                                                                             use spaces between cinder blocks, house        forage up to several kilometers from
a brief overview of bumble bee diversity
                                                                                                                                             foundations, abandoned furniture and           their colonies in search of nectar and
and natural history to provide context
                                                                                                                                             decks as protection for their growing          pollen, most species probably travel
for the subsequent discussions. We then
                                                                                                                                             colonies.                                      no more than 600-1,700 m (1/3 – 1 mi)
review the conservation status of bumble
                                                                                                                                                                                            to forage (Dramstad 1996, Hines and
bees and the potential causes for their                                                                                                      Once they locate a suitable nesting site, a
                                                                                                                                                                                            Hendrix 2005, Droege 2008, DeVore
decline. Finally, we discuss considerations                                                                                                  queen will modify it slightly and rear a
                                                                                                                                                                                            2009). Presumably shorter foraging trips
for managing for bumble bee diversity                                                                                                        brood (Kearns and Thomson 2001). A
                                                                                                                                                                                            are both safer and more energy-efficient. The
and abundance. Many of the resulting                                                                                                         few weeks later, the first workers emerge.
                                                                                                                                                                                            desert subspecies B. pensylvanicus sonorus can
recommendations apply to other native                                                                                                        These workers tend the young, maintain
                                                                                                                                                                                            ascend as much as 1,000 vertical meters (0.6 mi)
pollinators besides bumble bees, especially                                                                                                  the nest, and assume the food provision
                                                                                                                                                                                            on a daily basis in search of food (Schmidt and
ground-nesting bees. Much research                                                                                                           duties. The queen rarely, or never, leaves
                                              Figure 1. Documented bumble bee diversity in states or provinces for which                                                                    Jacobson 2005).
on bumble bee conservation occurs in                                                                                                         the nest again. Like most birds, bumble
                                              adequate data are available. Figures for some states may still represent
Europe, so we draw on this information        underestimates.                                                                                bees incubate their eggs and larvae to         North American bumble bees have been documented

4                                 Conservation and Management of North American Bumble Bees                                                                                                 NatureServe and the U.S. Forest Service                                      5
Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
where appropriate. The biblio-    and Europe. As in the rest of the world,           group of North American bumble              varying degrees with body heat to speed growth. This
                                                                                                                                                                                                                                                   Bombus insularis.
                                                       graphic references provide an entry   bumble bee diversity in North America              bees, occurring from subtropical to         adaptation is probably among the reasons why
                                                                                                                                                                                                                                                   Photo James Strange
                                                point into the growing literature on         is lowest in the southern lowlands and             boreal zones.                               bumble bees can thrive in cool conditions. As in
                                              bumble bees. Because scientific papers on      highest in cooler northern and mountain            Subterraneobombus (2 species)—A             all social bees, workers are females. Workers
                                              bumble bees are being published with in-       regions (Figure 1). For example, most              long-tongued, underground-nesting           do not mate, but can reproduce by laying
Introduction                                  creasing frequency (Goulson et al. 2010),      bumble bees in Arizona occur only in the           group primarily occurring in open           unfertilized eggs, producing males. At the
                                              we recognize that this document provides       mountains. This pattern is opposite of             northern and montane areas, such as         end of the colony cycle, queens also lay
Bumble bees are a familiar component of
                                              a snapshot of the state of our current         most plant and vertebrate groups, which            meadows.                                    unfertilized eggs that become males.
our terrestrial fauna. In the past, sight-
                                              knowledge and that subsequent research         generally decrease in diversity with               Thoracobombus (2 species)—A wide-
ing a bumble bee may have elicited no                                                                                                                                                       If nectar and pollen resources are ad-
                                              will fill in some of the knowledge gaps we     latitude.                                          spread group occurring throughout
more than a mental note to avoid getting                                                                                                                                                    equate, the colony will produce males
                                              identify here.                                                                                    the Northern Hemisphere as well as
stung or at most wonderment at how they                                                      In North America, the genus Bombus                                                             and new queens from about June to
can be active on high mountains or in                                                        comprises eight subgenera. These are:              New World tropical mountains. In            October, depending on the species,
cold climates. Today we pay them much         Diversity                                         Alpinobombus (4 species)—Bumble                 North America these species have            latitude and elevation. The males
more attention. Precipitous population                                                           bees of the arctic and high alpine areas.      long tongues and tend to nest above         and queens feed and then mate.
declines have affected several species,       Of the 250 species of bumble bees recog-                                                          ground.                                     In the fall, the new queens locate
                                              nized by taxonomists, approximately 46            Bombias (2 species)—A small group
creating cause for conservation concern.                                                         of bumble bees that occur primarily in                                                     a suitable site to overwinter (for
In addition, the loss of introduced honey     occur in the U.S. and Canada (See Ap-                                                                                                         example, mulch, rotting logs, or
bees (Apis mellifera) in both managed and     pendix for notes on species classification         open grasslands.                            Natural History                                loose soil). The males, workers,
                                              used here). All North American species            Bombus (5 species)—“Typical”
feral colonies has increased the need for                                                                                                    Annual Cycle.— North American                  and old queen all die by the
                                              are native to the continent. Most species          bumble bees that occur in a variety of
native pollinator species. Bumble bees are                                                                                                   bumble bee species vary somewhat in            onset of winter.
                                              have fairly broad ranges either east or            temperate and boreal habitats.
generalist pollinators, performing a key                                                                                                     their natural history. Bumble bees gener-
                                              west of the Rockies or across northern            Cullumanobombus (5 species)—Most-                                                           Foraging and nutrition.—
function in their ecosystems. They also                                                                                                      ally produce one generation per year. In
                                              Canada, although a few such as Bom-                ly bumble bees of high alpine grass-                                                       The workers gather nectar and
form a significant portion of the native                                                                                                     the spring, queens emerge from hiberna-
                                              bus franklini in northern California and           lands and semi-desert.                                                                     pollen to satisfy both their own
insect community that pollinates crops                                                                                                       tion to feed on flower nectar and search
                                              southern Oregon have restricted ranges.           Psithyrus (6 species)—“Cuckoo” bees                                                         nutritional needs and those
worth $3 billion each year in the United                                                                                                     for nest sites, which may be above or
                                              Six species, including three of the four           that parasitize nests of other bumble                                                      of the nest. Adults depend
States (Losey and Vaughan 2006). For                                                                                                         below ground, or either, depending on
                                              North American species in the subgenus             bees.                                                                                      on nectar for carbohydrates
both of these reasons, land managers are                                                                                                     the species (Thorp et al. 1983, Kearns
                                              Alpinobombus extend their ranges to Asia                                                                                                      and gather pollen as a protein
increasingly interested in bumble bee                                                           Pyrobombus (20 species) —The largest         and Thomson 2001, McFrederick and
                                                                                                                                                                                            source for larvae. A queen
conservation and management (Goulson                                                                                                         LeBuhn 2006). Bumble bees frequently
                                                                                                                                                                                            bumble bee forages for nectar
et al. 2010).                                                                                                                                inhabit abandoned rodent nests, probably
                                                                                                                                                                                            when she emerges in the spring,
                                                                                                                                             because these structures insulate the bees
This document summarizes recent                                                                                                                                                             and for another month or more
                                                                                                                                             from cold temperatures. Nests also tend to
information about bumble bee declines                                                                                                                                                       while she alone rears the first
                                                                                                                                             be constructed in areas with south facing
and their management in North America.                                                                                                                                                      brood of workers, during which
                                                                                                                                             exposures. Species nesting above ground
By “bumble bee”, we refer to species of                                                                                                                                                     time she must also collect pollen to
                                                                                                                                             may use long grass or hay stacks. A few
the genus Bombus (Hymenoptera, Api-                                                                                                                                                         feed her young.
                                                                                                                                             species will use tree cavities or bird boxes
dae), including the cuckoo bumble bees
                                                                                                                                             as nest sites. In urban areas, bumble bees     Although some bumble bees can
in the subgenus Psithyrus. We start with
                                                                                                                                             use spaces between cinder blocks, house        forage up to several kilometers from
a brief overview of bumble bee diversity
                                                                                                                                             foundations, abandoned furniture and           their colonies in search of nectar and
and natural history to provide context
                                                                                                                                             decks as protection for their growing          pollen, most species probably travel
for the subsequent discussions. We then
                                                                                                                                             colonies.                                      no more than 600-1,700 m (1/3 – 1 mi)
review the conservation status of bumble
                                                                                                                                                                                            to forage (Dramstad 1996, Hines and
bees and the potential causes for their                                                                                                      Once they locate a suitable nesting site, a
                                                                                                                                                                                            Hendrix 2005, Droege 2008, DeVore
decline. Finally, we discuss considerations                                                                                                  queen will modify it slightly and rear a
                                                                                                                                                                                            2009). Presumably shorter foraging trips
for managing for bumble bee diversity                                                                                                        brood (Kearns and Thomson 2001). A
                                                                                                                                                                                            are both safer and more energy-efficient. The
and abundance. Many of the resulting                                                                                                         few weeks later, the first workers emerge.
                                                                                                                                                                                            desert subspecies B. pensylvanicus sonorus can
recommendations apply to other native                                                                                                        These workers tend the young, maintain
                                                                                                                                                                                            ascend as much as 1,000 vertical meters (0.6 mi)
pollinators besides bumble bees, especially                                                                                                  the nest, and assume the food provision
                                                                                                                                                                                            on a daily basis in search of food (Schmidt and
ground-nesting bees. Much research                                                                                                           duties. The queen rarely, or never, leaves
                                              Figure 1. Documented bumble bee diversity in states or provinces for which                                                                    Jacobson 2005).
on bumble bee conservation occurs in                                                                                                         the nest again. Like most birds, bumble
                                              adequate data are available. Figures for some states may still represent
Europe, so we draw on this information        underestimates.                                                                                bees incubate their eggs and larvae to         North American bumble bees have been documented

4                                 Conservation and Management of North American Bumble Bees                                                                                                 NatureServe and the U.S. Forest Service                                      5
Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
visiting hundreds of native and intro-                    ated with more                                                                     tended consequence of causing the demise     ing rarity, threats, and population trends      range (Colla and Packer 2008, Grixti et al.
duced plant genera (Robertson 1929,                   open habitat (Colla                                                                    of several native bumble bees (see Causes    (Master et al. 2009). Of the North Ameri-       2008), but not as sharply as other declin-
Mitchell 1962, Colla and Dumesh 2010).           and Dumesh 2010). The                                                                       of Declines).                                can bumble bee species, nearly four-fifths      ing species. This species, B. vagans, is still
Some species are more generalized in           disappearance of bumble                                                                                                                    are globally secure (Figure 2, Appendix).       regularly found across its range. Several
their foraging preferences than others,        bees in the fall appears to                                                                                                                Severe declines in North America are            other Pyrobombus have been documented
but none appear to be highly specialized.      be timed with the passing                                                                     Conservation Status                          so far limited to eight species in three        as increasing. The North American spe-
In one study in Iowa prairie remnants,         of native fall flowers and                                                                    Declines in bumble bees and other pol-       subgenera, including all four North             cies in subgenera Alpinobombus, Cullo-
bumble bees foraged at 43 of 150 species       often precedes the first frost                                                                linators worldwide are documented in         American endemic species of subgenus            manbombus, and Subterraneobombus
of flowers available (Hines and Hendrix        and leaf fall (D. Schweitzer,                                                                 numerous studies (Goulson et al. 2005,       Bombus (the species B. moderatus is appar-      all appear to have stable populations
2005). However, the extent of specialism       pers. obs.).                                                                                  Kluser and Peduzzi 2007, Colla and           ently not declining, but its status is poorly   although rigorous range-wide monitoring
at the colony or individual level is largely                                                                                                 Packer 2008, Brown and Paxton 2009,          documented), B. pensylvanicus, and three        data are mostly lacking.
                                               Nest usurpation.— Spe-
unknown.                                                                                                                                     Evans et al. 2008, Williams et al. 2009,     species of subgenus Psithyrus.  In subge-
                                               cies of subgenus Psithyrus
                                                                                                                                             Winfree 2010, Committee on the Status        nus Bombus, B. franklini may already be
Activity and cold tolerance.—Bumble            have no worker caste of their own.
                                                                                            Figure 2. Proportion of North American           of Pollinators in North America 2007,        extinct and B. affinis, a common species        Causes of Declines
bees are well known to fly when condi-         Females can reproduce only by taking                          bumble bee species at risk.     Cameron et al. 2011a). Regional studies      in the early 1990s, may be extirpated in        Hypotheses about bumble bee declines in
tions are too cold for most other insects      over a nest of another species. Workers
                                                                                                                                             with adequate baseline data invariably       90% of its range (Williams and Osborne          North American can be divided into two
(e.g. cloudy or cool days, or early in the     in usurped nests tend the offspring of the
                                                                                             Workers of other species, such as B.            show that some bumble bees are in recent     2009; Figure 3). The latter species is now      classes. The first class, relating to the di-
morning before other diurnal insects are       replacement queen. Entomologists have
                                                                                             pensylvanicus, and B. fervidus can be very      decline (Giles and Ascher 2006, Colla and    listed as Endangered by the Committee           rect and indirect effects of climate change
active). They have a low surface area to       not fully documented the host breadth of
                                                                                             aggressive around their nests (Thorp et al.     Packer 2008, Grixti et al. 2009, Cameron     on the Status of Endangered Wildlife in         and habitat loss and degradation due to
volume ratio compared to other insects,        North American Psithyrus. Bombus insu-
                                                                                             1983, Kearns and Thomson 2001), likely          et al. 2011b). However, the status of        Canada (COSEWIC). The status of the             agricultural intensification, can explain
are well insulated, and can generate body      laris preys on several subgenera, whereas
                                                                                             a behavioral adaptation to their above-         many species throughout their ranges is      cuckoo bees, subgenus Psithyrus, is similar     gradual population declines and range
heat using their thoracic muscles. Bumble      B. citrinus is apparently a specialist on
                                                                                             ground nesting habits.                          poorly known. Habitat loss in areas with     to their hosts. Two species that commonly       restrictions in bumble bees worldwide. A
bees have been reported flying at slightly     subgenus Pyrobombus. Bombus ashtoni
                                                                                                                                             intensive agriculture can cause regional     parasitize species in Pyrobombus appear to      second class of hypotheses addresses the
sub-freezing temperatures (Heinrich            and B. suckleyi seem to be specialists on     Pollination.—Bumble bees are impor-
                                                                                                                                             extirpations of formerly common species      be doing well, while three that parasitize      swift and widespread declines restricted
1979). This ability to fly in cold weather     the subgenus Bombus (Williams 2008b,          tant generalist pollinators of native plants
                                                                                                                                             (Grixti et al. 2009, Williams et al. 2009,   species of subgenera Bombus and Thora-          to endemic North American species.
is undoubtedly a factor in the success         Laverty and Harder 1988), and B. variabi- and agricultural crops. The list of flowers
                                                                                                                                             Winfree 2010).                               cobombus are in serious declines and may        These hypotheses center on the “spillover”
of bumble bees in cool to frigid climates      lis appears to be a specialist on B. pensyl-  visited by bumble bees is vast (Goulson                                                      have disappeared from most if not all of        of pathogens from bumble bees imported
throughout much of the world.                  vanicus. Queens of subgenera Alpinobom- 2010, Kearns and Thomson 2001, Thorp                  To determine the conservation status of      their ranges.                                   from overseas.
                                               bus and Bombus sometimes usurp nests          et al. 1983). Theoretical studies have un-      North American bumble bees, Nature-
Bumble bees’ seasonal activity differs
                                               of their own or closely related species       derscored the importance of generalists in      Serve assessed all species according to      One species in the subgenus Pyrobombus          A recent meta-analysis of bumble bees in
among species. In the Mid-Atlantic states,
                                               (Richards 1973, Goulson 2010).                maintaining pollinator networks and com-        their standard assessment factors, includ-   appears to be declining in some parts of its    North America, Europe and China has
activity starts about the end of March for
                                                                                             munities of flowering plants (Memmott et                                                                                                     suggested that species which emerge later
the earliest species and becomes minimal       Aggression.—Bumble bees occasion-
                                                                                             al. 2004). One empirical study in Europe                                                                                                     in the year or have narrow climatic niches
in October (Droege 2008). Some early           ally sting when their nest is disturbed,
                                                                                             confirmed this prediction, demonstrating                                                                                                     are likely more vulnerable to these above
species such as B. impatiens are active        but rarely do so otherwise. Queens and
                                                                                             that the abundance of insect-pollinated                                                                                                      threats (Williams et al. 2009). Hypoth-
into the fall, while others end their cycles   workers can sting, but, as in all bees and
                                                                                             plants declined in areas where bumble                                                                                                        eses that failed to explain vulnerability
in June or July (e.g., B. bimaculatus).        wasps, males cannot. To humans, the
                                                                                             bees and other native bees had become                                                                                                        include competition with congeners, food
Others, including B. pensylvanicus, emerge     stings are briefly painful but not danger-
                                                                                             extirpated (Biesmeijer et al. 2006).                                                                                                         specialization, phenology, body size, and
from their overwintering sites later in        ous, except to a few people who develop
spring. The parasitic cuckoo species also      serious allergic reactions. Bumble bee                                                                                                                                                     range extent. However, some of these
                                                                                             Bumble bees exhibit a behavior known
tend to have shorter cycles. In northern       hives contain far fewer individuals than                                                                                                                                                   factors may be more important regionally
                                                                                             as “buzz pollination,” in which the bee
New England, activity begins a month or        those of honey bees, and workers of most                                                                                                                                                   than in global analyses. For example, one
                                                                                             vibrates her wing muscles while holding
more later and ends a few weeks earlier. A     species are far less aggressive than wasps                                                                                                                                                 European study showed that species uti-
                                                                                             the flower with her jaws, causing the re-
good rule of thumb in much of the eastern      and hornets. Bumble bee stingers are not                                                                                                                                                   lizing smaller numbers of pollen sources
                                                                                             lease of large amounts of pollen. Growers
U.S. is that queens of the early-emerging      barbed as in honey bees and therefore do                                                                                                                                                   have become rarer since the middle of the
                                                                                             of crops such as tomatoes, peppers, and
species become numerous soon after red         not remain in the victim. However, this                                                                                                                                                    twentieth century (Kleijn and Raemak-
                                                                                             cranberries prize this behavior because
maple (Acer rubrum) blossoms drop and          also means a bumble bee can sting more                                                                                                                                                     ers 2008). A brief summary of the major
                                                                                             it leads to better fruit set than pollination
just before blueberry (Vaccinium spp.)         than once when provoked. Some species,                                                                                                                                                     hypotheses follows.
                                                                                             by honey bees. A commercial bumble
and other early Ericaceae flower. Early        such as B. impatiens, are remarkably non- bee industry has emerged to capitalize on                                                                                                        Habitat loss.—Because bumble bees
emerging species also tend to be associ-       aggressive when nesting around buildings. buzz pollination for greenhouse tomato                                                                                                           often forage in open, disturbed habitats,
ated with woodland habitats, whereas the       This species is also safely managed for       farmers (Velthius and van Doorn 2006), a                                                                                                     the effects of habitat loss are harder to
                                                                                                                                             Figure 3. Distribution of the Rusty-patched Bumble Bee, Bombus affinis.
later emerging species tend to be associ-      crop pollination, including in greenhouses. development that may have had the unin-                                                                                                        measure than for animals that depend
                                                                                                                                             Source: NatureServe 2009.

6                                   Conservation and Management of North American Bumble Bees                                                                                              NatureServe and the U.S. Forest Service                                                     7
visiting hundreds of native and intro-                    ated with more                                                                     tended consequence of causing the demise     ing rarity, threats, and population trends      range (Colla and Packer 2008, Grixti et al.
duced plant genera (Robertson 1929,                   open habitat (Colla                                                                    of several native bumble bees (see Causes    (Master et al. 2009). Of the North Ameri-       2008), but not as sharply as other declin-
Mitchell 1962, Colla and Dumesh 2010).           and Dumesh 2010). The                                                                       of Declines).                                can bumble bee species, nearly four-fifths      ing species. This species, B. vagans, is still
Some species are more generalized in           disappearance of bumble                                                                                                                    are globally secure (Figure 2, Appendix).       regularly found across its range. Several
their foraging preferences than others,        bees in the fall appears to                                                                                                                Severe declines in North America are            other Pyrobombus have been documented
but none appear to be highly specialized.      be timed with the passing                                                                     Conservation Status                          so far limited to eight species in three        as increasing. The North American spe-
In one study in Iowa prairie remnants,         of native fall flowers and                                                                    Declines in bumble bees and other pol-       subgenera, including all four North             cies in subgenera Alpinobombus, Cullo-
bumble bees foraged at 43 of 150 species       often precedes the first frost                                                                linators worldwide are documented in         American endemic species of subgenus            manbombus, and Subterraneobombus
of flowers available (Hines and Hendrix        and leaf fall (D. Schweitzer,                                                                 numerous studies (Goulson et al. 2005,       Bombus (the species B. moderatus is appar-      all appear to have stable populations
2005). However, the extent of specialism       pers. obs.).                                                                                  Kluser and Peduzzi 2007, Colla and           ently not declining, but its status is poorly   although rigorous range-wide monitoring
at the colony or individual level is largely                                                                                                 Packer 2008, Brown and Paxton 2009,          documented), B. pensylvanicus, and three        data are mostly lacking.
                                               Nest usurpation.— Spe-
unknown.                                                                                                                                     Evans et al. 2008, Williams et al. 2009,     species of subgenus Psithyrus.  In subge-
                                               cies of subgenus Psithyrus
                                                                                                                                             Winfree 2010, Committee on the Status        nus Bombus, B. franklini may already be
Activity and cold tolerance.—Bumble            have no worker caste of their own.
                                                                                            Figure 2. Proportion of North American           of Pollinators in North America 2007,        extinct and B. affinis, a common species        Causes of Declines
bees are well known to fly when condi-         Females can reproduce only by taking                          bumble bee species at risk.     Cameron et al. 2011a). Regional studies      in the early 1990s, may be extirpated in        Hypotheses about bumble bee declines in
tions are too cold for most other insects      over a nest of another species. Workers
                                                                                                                                             with adequate baseline data invariably       90% of its range (Williams and Osborne          North American can be divided into two
(e.g. cloudy or cool days, or early in the     in usurped nests tend the offspring of the
                                                                                             Workers of other species, such as B.            show that some bumble bees are in recent     2009; Figure 3). The latter species is now      classes. The first class, relating to the di-
morning before other diurnal insects are       replacement queen. Entomologists have
                                                                                             pensylvanicus, and B. fervidus can be very      decline (Giles and Ascher 2006, Colla and    listed as Endangered by the Committee           rect and indirect effects of climate change
active). They have a low surface area to       not fully documented the host breadth of
                                                                                             aggressive around their nests (Thorp et al.     Packer 2008, Grixti et al. 2009, Cameron     on the Status of Endangered Wildlife in         and habitat loss and degradation due to
volume ratio compared to other insects,        North American Psithyrus. Bombus insu-
                                                                                             1983, Kearns and Thomson 2001), likely          et al. 2011b). However, the status of        Canada (COSEWIC). The status of the             agricultural intensification, can explain
are well insulated, and can generate body      laris preys on several subgenera, whereas
                                                                                             a behavioral adaptation to their above-         many species throughout their ranges is      cuckoo bees, subgenus Psithyrus, is similar     gradual population declines and range
heat using their thoracic muscles. Bumble      B. citrinus is apparently a specialist on
                                                                                             ground nesting habits.                          poorly known. Habitat loss in areas with     to their hosts. Two species that commonly       restrictions in bumble bees worldwide. A
bees have been reported flying at slightly     subgenus Pyrobombus. Bombus ashtoni
                                                                                                                                             intensive agriculture can cause regional     parasitize species in Pyrobombus appear to      second class of hypotheses addresses the
sub-freezing temperatures (Heinrich            and B. suckleyi seem to be specialists on     Pollination.—Bumble bees are impor-
                                                                                                                                             extirpations of formerly common species      be doing well, while three that parasitize      swift and widespread declines restricted
1979). This ability to fly in cold weather     the subgenus Bombus (Williams 2008b,          tant generalist pollinators of native plants
                                                                                                                                             (Grixti et al. 2009, Williams et al. 2009,   species of subgenera Bombus and Thora-          to endemic North American species.
is undoubtedly a factor in the success         Laverty and Harder 1988), and B. variabi- and agricultural crops. The list of flowers
                                                                                                                                             Winfree 2010).                               cobombus are in serious declines and may        These hypotheses center on the “spillover”
of bumble bees in cool to frigid climates      lis appears to be a specialist on B. pensyl-  visited by bumble bees is vast (Goulson                                                      have disappeared from most if not all of        of pathogens from bumble bees imported
throughout much of the world.                  vanicus. Queens of subgenera Alpinobom- 2010, Kearns and Thomson 2001, Thorp                  To determine the conservation status of      their ranges.                                   from overseas.
                                               bus and Bombus sometimes usurp nests          et al. 1983). Theoretical studies have un-      North American bumble bees, Nature-
Bumble bees’ seasonal activity differs
                                               of their own or closely related species       derscored the importance of generalists in      Serve assessed all species according to      One species in the subgenus Pyrobombus          A recent meta-analysis of bumble bees in
among species. In the Mid-Atlantic states,
                                               (Richards 1973, Goulson 2010).                maintaining pollinator networks and com-        their standard assessment factors, includ-   appears to be declining in some parts of its    North America, Europe and China has
activity starts about the end of March for
                                                                                             munities of flowering plants (Memmott et                                                                                                     suggested that species which emerge later
the earliest species and becomes minimal       Aggression.—Bumble bees occasion-
                                                                                             al. 2004). One empirical study in Europe                                                                                                     in the year or have narrow climatic niches
in October (Droege 2008). Some early           ally sting when their nest is disturbed,
                                                                                             confirmed this prediction, demonstrating                                                                                                     are likely more vulnerable to these above
species such as B. impatiens are active        but rarely do so otherwise. Queens and
                                                                                             that the abundance of insect-pollinated                                                                                                      threats (Williams et al. 2009). Hypoth-
into the fall, while others end their cycles   workers can sting, but, as in all bees and
                                                                                             plants declined in areas where bumble                                                                                                        eses that failed to explain vulnerability
in June or July (e.g., B. bimaculatus).        wasps, males cannot. To humans, the
                                                                                             bees and other native bees had become                                                                                                        include competition with congeners, food
Others, including B. pensylvanicus, emerge     stings are briefly painful but not danger-
                                                                                             extirpated (Biesmeijer et al. 2006).                                                                                                         specialization, phenology, body size, and
from their overwintering sites later in        ous, except to a few people who develop
spring. The parasitic cuckoo species also      serious allergic reactions. Bumble bee                                                                                                                                                     range extent. However, some of these
                                                                                             Bumble bees exhibit a behavior known
tend to have shorter cycles. In northern       hives contain far fewer individuals than                                                                                                                                                   factors may be more important regionally
                                                                                             as “buzz pollination,” in which the bee
New England, activity begins a month or        those of honey bees, and workers of most                                                                                                                                                   than in global analyses. For example, one
                                                                                             vibrates her wing muscles while holding
more later and ends a few weeks earlier. A     species are far less aggressive than wasps                                                                                                                                                 European study showed that species uti-
                                                                                             the flower with her jaws, causing the re-
good rule of thumb in much of the eastern      and hornets. Bumble bee stingers are not                                                                                                                                                   lizing smaller numbers of pollen sources
                                                                                             lease of large amounts of pollen. Growers
U.S. is that queens of the early-emerging      barbed as in honey bees and therefore do                                                                                                                                                   have become rarer since the middle of the
                                                                                             of crops such as tomatoes, peppers, and
species become numerous soon after red         not remain in the victim. However, this                                                                                                                                                    twentieth century (Kleijn and Raemak-
                                                                                             cranberries prize this behavior because
maple (Acer rubrum) blossoms drop and          also means a bumble bee can sting more                                                                                                                                                     ers 2008). A brief summary of the major
                                                                                             it leads to better fruit set than pollination
just before blueberry (Vaccinium spp.)         than once when provoked. Some species,                                                                                                                                                     hypotheses follows.
                                                                                             by honey bees. A commercial bumble
and other early Ericaceae flower. Early        such as B. impatiens, are remarkably non- bee industry has emerged to capitalize on                                                                                                        Habitat loss.—Because bumble bees
emerging species also tend to be associ-       aggressive when nesting around buildings. buzz pollination for greenhouse tomato                                                                                                           often forage in open, disturbed habitats,
ated with woodland habitats, whereas the       This species is also safely managed for       farmers (Velthius and van Doorn 2006), a                                                                                                     the effects of habitat loss are harder to
                                                                                                                                             Figure 3. Distribution of the Rusty-patched Bumble Bee, Bombus affinis.
later emerging species tend to be associ-      crop pollination, including in greenhouses. development that may have had the unin-                                                                                                        measure than for animals that depend
                                                                                                                                             Source: NatureServe 2009.

6                                   Conservation and Management of North American Bumble Bees                                                                                              NatureServe and the U.S. Forest Service                                                     7
on more natural habitats. Some agricul-                                                         that feed on pesticide-contaminated food.       native bumble bees corresponds with the        Several studies have found bumble bee management to be com-
tural habitats, such as hay meadows and                 to climate change are those that        Some pesticides, such as spinosad, cause        accelerated transportation of bumble bee       patible with agricultural practices. Moderate grazing can be
pastures, are suitable to bumble bees                occupy narrow ranges near the Pacific      no direct mortality but instead reduce          colonies in the mid and late 1990s after       beneficial to bees in the western U.S. (DeBano 2006, Black
                                                                                                                                                                                                                                                                      Providing
(Carvell 2002, Goulson 2010, McFreder-           coast, such as B. crotchii in oak woodland,    foraging efficiency (Goulson 2010). The         the development of techniques for domes-       et al. 2007). In the northwestern U.S., agricultural areas          Artificial
ick and LeBuhn 2006, Rao and Stephen             chaparral, and deserts and B. sitkensis and    toxicity of specific pesticides is better       tication. The actual pathogens implicated      with blueberry (Vaccinium spp.) and red clover (Trifo-             Nests      for
2010). Some species can even prosper in          B. caliginosus in cooler coastal climates.     known for honey bees than bumble bees,          are the protozoans Crithidia bombi and         lium pratense) can support abundant populations of               Bumble Bees
urban gardens and parks (McFrederick             Elsewhere, isolated high alpine popula-        but the available data suggest that toxicity    Nosema bombi, although other pathogens         several species of bumble bees (Rao and Stephen
and LeBuhn 2006, Matteson et al. 2008,           tions of several species may disappear due     to bumble bees is generally similar to that     may also play important roles (Meeus et        2010). In any region, the keys are maintaining a               Where nesting sites are
Matteson and Langellotto 2009). The              to climate change.                             of honey bees (Alston and Tepedino 2000).       al. 2011). Unfortunately, due to the lack      reliable supply of nectar throughout the breeding            limited, artificial nests
spread of Eurasian clovers (Trifolium)           Phenology of queen emergence.—                 An application of pesticides to control         of both stable populations of declining        season, providing unplowed nesting habitats,
                                                                                                                                                                                                                                                          are an option to increase
and vetches (Vicia, Coronilla) has ben-          Some authors suggest that species in           spruce budworm in New Brunswick il-             species in affected regions and informa-       and limiting exposure to insecticides. Organic
efited some butterflies (Schweitzer 2006)                                                       lustrates the potential effects of pesticides   tion about native pathogens, researchers       farming practices may help promote bumble                bumble bee populations
                                                 which queens become active later in
and presumably bumble bees as well.              the season are at a disadvantage due to        on bumble bees and other pollinators. In        cannot directly test the effects of these      bee populations, although other factors can             (MacCulloch 2007, Kearns
Nevertheless, intensive agriculture has          competition for nest sites and vulnerability   this case, the pesticide application caused     pathogens relative to other threats.           confound research results (Winfree 2010).              and Thomson 2001). The basic
caused local and regional declines in the        to losses of food plants that are impor-       blueberry crop losses due to reduced avail-                                                    Some bumble bee species can benefit from
Midwest as well as Europe (Grixti et al.                                                        ability of pollinators. In addition, reduced                                                   foraging in suburban and urban gardens,               artificial nest is a box fitted with
                                                 tant in mid to late colony development
2009, Williams et al. 2009). The mismatch        (Williams et al. 2009). In North America,      pollination of nearby native species caused     Conservation and                               (Frankie et al. 2009, McFrederick and                a plastic pipe as an entrance
between the time scale of habitat loss           nest competition is documented in urban        a local wild berry shortage and conse-          Management                                     LeBuhn 2006). Manicured lawns and golf              tunnel. The box can be made out
(before the mid 20th century) and rapidly        areas of San Francisco where the early         quently increased the number of birds                                                          courses with heavy pesticide use and de-
                                                                                                                                                To complete their annual cycle, all bumble                                                        of wood (such as exterior grade
declining North American species (since          B. vosnenskii apparently excludes the          foraging on cultivated blueberries (Kevan                                                      void of flowers are among the least useful
                                                                                                                                                bees need nesting habitat, flowers for nu-
the mid 1990s) suggests that habitat loss is     later B. caliginosus and B. sitkensis from     1974). Bumble bee colonies can absorb the                                                      nesting and foraging habitats.                     plywood) or Styrofoam (such as
                                                                                                                                                trition, and a place for queens to overwin-
unlikely to explain these declines (Grixti       the limited supply of subterranean nest        loss of a few workers to pesticides in sum-                                                                                                        an old cooler). Dimensions vary
                                                                                                                                                ter. They must also avoid lethal and sub-      On more natural lands, management
et al. 2009).                                    sites (McFrederick and LeBuhn 2006).           mer, but worker loss can more seriously
                                                                                                                                                lethal chemicals and pathogens. We know        should focus on maintaining diverse as-            but 8 x 8 x 6 inches (20 x 20 x 15
                                                 However, none of these species appear to       impact colony survival in spring before
Climate change.—Although climate                                                                                                                very little about overwintering needs, so      semblages of primarily native flora, such
                                                 be declining globally, and there is no evi-    colonies have built up significant numbers                                                                                                        cm) is standard. The entrance
change has been suggested as a cause of                                                                                                         the following summary of the growing           that flowers would be constantly available
                                                 dence that phenology is linked to declines     of workers (Goulson 2010). Additionally,                                                                                                          hole should be ¼ inch (0.65 cm) in
declines and may be affecting bumble                                                                                                            literature on bumble bee conservation and      throughout the nesting season. In prairie
                                                 of bumble bees in North America where          sub-lethal compounds may accumulate in
bees in some places, there is as of yet little                                                                                                  management will focus on nesting and           regions, restoration of native prairie              diameter. The box can be placed
                                                 both early- and late-emerging species are      the colony and affect the overall reproduc-
direct evidence that climate change is                                                                                                          foraging needs.                                species and elimination of plowing, for ex-         on the ground or 6-12 inches
                                                 among the five non-parasitic species that      tive fitness of the colony. Species which
responsible for global declines of wide-                                                                                                                                                       ample along roadsides, can result in richer
                                                 are in severe decline.                         may be more vulnerable to pesticide use         General habitat needs.—Bumble bees                                                                 (15-30 cm) underground with the
spread species. In North America, most                                                                                                                                                         bumble bee faunas (Hopwood 2008).
                                                                                                include the above ground nesting spe-           can be atypical targets for conservation
species occur (at least formerly) in a wide      Tongue length and foraging ecol-                                                                                                                                                                   entrance tube connecting the box
                                                                                                cies (e.g., subgenus Thoracobombus) and         efforts. In contrast to many other rare        The extent to which bumble bees use for-
array of climates, ranging through more          ogy.—Bumble bees with long tongues are                                                                                                                                                              to the surface. Southern expo-
                                                                                                species with long colony cycles that can        or endangered species, bumble bees may         ests is a major knowledge gap for eastern
than ten degrees of latitude and some            generally more specialized foragers. Al-       accumulate toxins over the spring, sum-         not require forest cover or even natural       North American bumble bees, although                   sures, especially on a slight em-
from coast to coast. Moreover, most of           though some authors have suggested that        mer and fall. Pesticides likely contribute to   habitats to maintain large and species-rich    some species such as B. vagans seem to                  bankment, are best. Whatever
the North American species that have             specialists (and therefore longer-tongued      bumble bee declines in areas of intensive       populations. Especially in eastern North       be associated with wooded habitats (Colla
declined precipitously had large ranges.         species) should be more likely to decline,     agriculture, but are unlikely to be respon-     America, a hayfield or powerline cut with                                                               the design or placement, the
                                                                                                                                                                                               and Dumesh 2010). Similarly, the effects of
Even B. affinis ranged from Maine to             no such pattern has emerged in North                                                                                                                                                                    box should contain insulation
                                                                                                sible for rapid, widespread declines (Colla     plentiful wildflowers may be all that is       standard forest management practices, such
Georgia and the Dakotas (Figure 3).              America (Grixti et al. 2009, Williams et al.   and Packer 2008, DeVore 2009).                  necessary for populations of a number of       as thinning or controlled burning, on bumble               in the form of upholsterer’s
Despite this large range, members of the         2009, Winfree 2010). One complication                                                          species (Russell et al. 2005). In fact, the    bees are mostly undocumented. Opening forest
subgenus Bombus do seem to be some-              with relating tongue length with forag-        Pathogen spillover.—Currently, the                                                                                                                         cotton or polyester fiberfill.
                                                                                                                                                endangered species Bombus affinis was          canopies often allows more flowering of under-
what climatically restricted as they occur       ing is that tongue length is individually      most compelling hypothesis to explain                                                                                                                       Reported reasons for fail-
                                                                                                                                                quite common in urban areas before its         story plants, which should favor bumble bees (but
mostly at high elevations in southern parts      variable with body size, whereas foraging      rapid declines is the spillover of pathogens
                                                                                                                                                collapse (Colla and Dumesh 2010). Re-          see Nesting Habitat for the danger posed by fires).            ure include ants, excess
of their ranges. Range breadth, combined         preferences are largely learned (Kearns        from managed to wild bumble bees (Colla
                                                                                                                                                gardless of the region, management activi-
with high mobility and dispersal ability,        and Thomson 2001). Direct measures of          et al. 2006, Otterstatter and Thomson                                                          Food supply.—Observations of nest failure due to                 moisture, or mam-
                                                                                                                                                ties should be aimed at improving flower
and the observed rapidity of declines seem       foraging specialization, however, indicate     2008, Williams et al. 2009, Goulson 2010,                                                      food limitation highlight the need for a reliable nectar           malian predators, so
                                                                                                                                                availability and providing potential nest-
to argue against climate change as being         a weak relationship with declines in Eu-       Meeus et al. 2011). Field documenta-                                                           and pollen supply when bumble bees are active from
                                                                                                                                                ing habitat (Blake et al. 2011). Specific                                                                          managers should be
a major factor in recent dramatic declines.      rope (Kleijn and Raemakers 2008).              tion of pathogen spillover and related                                                         spring to late summer (Goulson 2010). In both natural
                                                                                                                                                actions taken to achieve this objective will                                                                         on the lookout for
However, more research is needed to                                                             modeling show waves of parasites and                                                           and anthropogenic habitats, multiple nectar plants with
                                                 Pesticides.—Direct exposure to pesticides                                                      vary depending upon whether manage-
further investigate this.                                                                       pathogens spreading out from infested                                                          a succession of overlapping bloom periods are usually                   these problems.
                                                 can kill queen or worker bumble bees,                                                          ment is directed at agricultural, urban, or
                                                                                                commercial hives at multiple locations.                                                        required to satisfy this requirement. In some cases forag-
Species that may prove to be vulnerable          and cause minor to lethal effects to larvae                                                    more natural lands.
                                                                                                Moreover, the timing of decline onset in                                                       ing habitats as well as plant species will vary seasonally. In

8                                    Conservation and Management of North American Bumble Bees                                                                                                 NatureServe and the U.S. Forest Service                                                      9
on more natural habitats. Some agricul-                                                         that feed on pesticide-contaminated food.       native bumble bees corresponds with the        Several studies have found bumble bee management to be com-
tural habitats, such as hay meadows and                 to climate change are those that        Some pesticides, such as spinosad, cause        accelerated transportation of bumble bee       patible with agricultural practices. Moderate grazing can be
pastures, are suitable to bumble bees                occupy narrow ranges near the Pacific      no direct mortality but instead reduce          colonies in the mid and late 1990s after       beneficial to bees in the western U.S. (DeBano 2006, Black
                                                                                                                                                                                                                                                                      Providing
(Carvell 2002, Goulson 2010, McFreder-           coast, such as B. crotchii in oak woodland,    foraging efficiency (Goulson 2010). The         the development of techniques for domes-       et al. 2007). In the northwestern U.S., agricultural areas          Artificial
ick and LeBuhn 2006, Rao and Stephen             chaparral, and deserts and B. sitkensis and    toxicity of specific pesticides is better       tication. The actual pathogens implicated      with blueberry (Vaccinium spp.) and red clover (Trifo-             Nests      for
2010). Some species can even prosper in          B. caliginosus in cooler coastal climates.     known for honey bees than bumble bees,          are the protozoans Crithidia bombi and         lium pratense) can support abundant populations of               Bumble Bees
urban gardens and parks (McFrederick             Elsewhere, isolated high alpine popula-        but the available data suggest that toxicity    Nosema bombi, although other pathogens         several species of bumble bees (Rao and Stephen
and LeBuhn 2006, Matteson et al. 2008,           tions of several species may disappear due     to bumble bees is generally similar to that     may also play important roles (Meeus et        2010). In any region, the keys are maintaining a               Where nesting sites are
Matteson and Langellotto 2009). The              to climate change.                             of honey bees (Alston and Tepedino 2000).       al. 2011). Unfortunately, due to the lack      reliable supply of nectar throughout the breeding            limited, artificial nests
spread of Eurasian clovers (Trifolium)           Phenology of queen emergence.—                 An application of pesticides to control         of both stable populations of declining        season, providing unplowed nesting habitats,
                                                                                                                                                                                                                                                          are an option to increase
and vetches (Vicia, Coronilla) has ben-          Some authors suggest that species in           spruce budworm in New Brunswick il-             species in affected regions and informa-       and limiting exposure to insecticides. Organic
efited some butterflies (Schweitzer 2006)                                                       lustrates the potential effects of pesticides   tion about native pathogens, researchers       farming practices may help promote bumble                bumble bee populations
                                                 which queens become active later in
and presumably bumble bees as well.              the season are at a disadvantage due to        on bumble bees and other pollinators. In        cannot directly test the effects of these      bee populations, although other factors can             (MacCulloch 2007, Kearns
Nevertheless, intensive agriculture has          competition for nest sites and vulnerability   this case, the pesticide application caused     pathogens relative to other threats.           confound research results (Winfree 2010).              and Thomson 2001). The basic
caused local and regional declines in the        to losses of food plants that are impor-       blueberry crop losses due to reduced avail-                                                    Some bumble bee species can benefit from
Midwest as well as Europe (Grixti et al.                                                        ability of pollinators. In addition, reduced                                                   foraging in suburban and urban gardens,               artificial nest is a box fitted with
                                                 tant in mid to late colony development
2009, Williams et al. 2009). The mismatch        (Williams et al. 2009). In North America,      pollination of nearby native species caused     Conservation and                               (Frankie et al. 2009, McFrederick and                a plastic pipe as an entrance
between the time scale of habitat loss           nest competition is documented in urban        a local wild berry shortage and conse-          Management                                     LeBuhn 2006). Manicured lawns and golf              tunnel. The box can be made out
(before the mid 20th century) and rapidly        areas of San Francisco where the early         quently increased the number of birds                                                          courses with heavy pesticide use and de-
                                                                                                                                                To complete their annual cycle, all bumble                                                        of wood (such as exterior grade
declining North American species (since          B. vosnenskii apparently excludes the          foraging on cultivated blueberries (Kevan                                                      void of flowers are among the least useful
                                                                                                                                                bees need nesting habitat, flowers for nu-
the mid 1990s) suggests that habitat loss is     later B. caliginosus and B. sitkensis from     1974). Bumble bee colonies can absorb the                                                      nesting and foraging habitats.                     plywood) or Styrofoam (such as
                                                                                                                                                trition, and a place for queens to overwin-
unlikely to explain these declines (Grixti       the limited supply of subterranean nest        loss of a few workers to pesticides in sum-                                                                                                        an old cooler). Dimensions vary
                                                                                                                                                ter. They must also avoid lethal and sub-      On more natural lands, management
et al. 2009).                                    sites (McFrederick and LeBuhn 2006).           mer, but worker loss can more seriously
                                                                                                                                                lethal chemicals and pathogens. We know        should focus on maintaining diverse as-            but 8 x 8 x 6 inches (20 x 20 x 15
                                                 However, none of these species appear to       impact colony survival in spring before
Climate change.—Although climate                                                                                                                very little about overwintering needs, so      semblages of primarily native flora, such
                                                 be declining globally, and there is no evi-    colonies have built up significant numbers                                                                                                        cm) is standard. The entrance
change has been suggested as a cause of                                                                                                         the following summary of the growing           that flowers would be constantly available
                                                 dence that phenology is linked to declines     of workers (Goulson 2010). Additionally,                                                                                                          hole should be ¼ inch (0.65 cm) in
declines and may be affecting bumble                                                                                                            literature on bumble bee conservation and      throughout the nesting season. In prairie
                                                 of bumble bees in North America where          sub-lethal compounds may accumulate in
bees in some places, there is as of yet little                                                                                                  management will focus on nesting and           regions, restoration of native prairie              diameter. The box can be placed
                                                 both early- and late-emerging species are      the colony and affect the overall reproduc-
direct evidence that climate change is                                                                                                          foraging needs.                                species and elimination of plowing, for ex-         on the ground or 6-12 inches
                                                 among the five non-parasitic species that      tive fitness of the colony. Species which
responsible for global declines of wide-                                                                                                                                                       ample along roadsides, can result in richer
                                                 are in severe decline.                         may be more vulnerable to pesticide use         General habitat needs.—Bumble bees                                                                 (15-30 cm) underground with the
spread species. In North America, most                                                                                                                                                         bumble bee faunas (Hopwood 2008).
                                                                                                include the above ground nesting spe-           can be atypical targets for conservation
species occur (at least formerly) in a wide      Tongue length and foraging ecol-                                                                                                                                                                   entrance tube connecting the box
                                                                                                cies (e.g., subgenus Thoracobombus) and         efforts. In contrast to many other rare        The extent to which bumble bees use for-
array of climates, ranging through more          ogy.—Bumble bees with long tongues are                                                                                                                                                              to the surface. Southern expo-
                                                                                                species with long colony cycles that can        or endangered species, bumble bees may         ests is a major knowledge gap for eastern
than ten degrees of latitude and some            generally more specialized foragers. Al-       accumulate toxins over the spring, sum-         not require forest cover or even natural       North American bumble bees, although                   sures, especially on a slight em-
from coast to coast. Moreover, most of           though some authors have suggested that        mer and fall. Pesticides likely contribute to   habitats to maintain large and species-rich    some species such as B. vagans seem to                  bankment, are best. Whatever
the North American species that have             specialists (and therefore longer-tongued      bumble bee declines in areas of intensive       populations. Especially in eastern North       be associated with wooded habitats (Colla
declined precipitously had large ranges.         species) should be more likely to decline,     agriculture, but are unlikely to be respon-     America, a hayfield or powerline cut with                                                               the design or placement, the
                                                                                                                                                                                               and Dumesh 2010). Similarly, the effects of
Even B. affinis ranged from Maine to             no such pattern has emerged in North                                                                                                                                                                    box should contain insulation
                                                                                                sible for rapid, widespread declines (Colla     plentiful wildflowers may be all that is       standard forest management practices, such
Georgia and the Dakotas (Figure 3).              America (Grixti et al. 2009, Williams et al.   and Packer 2008, DeVore 2009).                  necessary for populations of a number of       as thinning or controlled burning, on bumble               in the form of upholsterer’s
Despite this large range, members of the         2009, Winfree 2010). One complication                                                          species (Russell et al. 2005). In fact, the    bees are mostly undocumented. Opening forest
subgenus Bombus do seem to be some-              with relating tongue length with forag-        Pathogen spillover.—Currently, the                                                                                                                         cotton or polyester fiberfill.
                                                                                                                                                endangered species Bombus affinis was          canopies often allows more flowering of under-
what climatically restricted as they occur       ing is that tongue length is individually      most compelling hypothesis to explain                                                                                                                       Reported reasons for fail-
                                                                                                                                                quite common in urban areas before its         story plants, which should favor bumble bees (but
mostly at high elevations in southern parts      variable with body size, whereas foraging      rapid declines is the spillover of pathogens
                                                                                                                                                collapse (Colla and Dumesh 2010). Re-          see Nesting Habitat for the danger posed by fires).            ure include ants, excess
of their ranges. Range breadth, combined         preferences are largely learned (Kearns        from managed to wild bumble bees (Colla
                                                                                                                                                gardless of the region, management activi-
with high mobility and dispersal ability,        and Thomson 2001). Direct measures of          et al. 2006, Otterstatter and Thomson                                                          Food supply.—Observations of nest failure due to                 moisture, or mam-
                                                                                                                                                ties should be aimed at improving flower
and the observed rapidity of declines seem       foraging specialization, however, indicate     2008, Williams et al. 2009, Goulson 2010,                                                      food limitation highlight the need for a reliable nectar           malian predators, so
                                                                                                                                                availability and providing potential nest-
to argue against climate change as being         a weak relationship with declines in Eu-       Meeus et al. 2011). Field documenta-                                                           and pollen supply when bumble bees are active from
                                                                                                                                                ing habitat (Blake et al. 2011). Specific                                                                          managers should be
a major factor in recent dramatic declines.      rope (Kleijn and Raemakers 2008).              tion of pathogen spillover and related                                                         spring to late summer (Goulson 2010). In both natural
                                                                                                                                                actions taken to achieve this objective will                                                                         on the lookout for
However, more research is needed to                                                             modeling show waves of parasites and                                                           and anthropogenic habitats, multiple nectar plants with
                                                 Pesticides.—Direct exposure to pesticides                                                      vary depending upon whether manage-
further investigate this.                                                                       pathogens spreading out from infested                                                          a succession of overlapping bloom periods are usually                   these problems.
                                                 can kill queen or worker bumble bees,                                                          ment is directed at agricultural, urban, or
                                                                                                commercial hives at multiple locations.                                                        required to satisfy this requirement. In some cases forag-
Species that may prove to be vulnerable          and cause minor to lethal effects to larvae                                                    more natural lands.
                                                                                                Moreover, the timing of decline onset in                                                       ing habitats as well as plant species will vary seasonally. In

8                                    Conservation and Management of North American Bumble Bees                                                                                                 NatureServe and the U.S. Forest Service                                                      9
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