A Comparative Life-Table Analysis of Sipha flava (Hemiptera: Aphididae) on Two Biofuel Hosts, Miscanthus ⴛ giganteus
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ECOLOGY AND BEHAVIOR
A Comparative Life-Table Analysis of Sipha flava (Hemiptera:
Aphididae) on Two Biofuel Hosts, Miscanthus ⴛ giganteus and
Saccharum spp.
G. R. PALLIPPARAMBIL,1,2 G. CHA,1 AND M. E. GRAY3
J. Econ. Entomol. 107(3): 1069Ð1075 (2014); DOI: http://dx.doi.org/10.1603/EC13263
ABSTRACT Among the insects reported in biofuel crops, the yellow sugarcane aphid, Sipha flava
(Forbes), is a potential pest of giant miscanthus, Miscanthus ⫻ giganteus Greef et Deu ex Hodkinson
et Renvoize (M⫻g) and energy cane ÔL79-1002Õ, Saccharum spp. L. We studied the biology of S. flava
on M⫻g and energy cane and estimated the development period, fecundity, longevity, intrinsic rate
of increase, doubling time, reproductive value, and survivorship curves. To demonstrate the host
suitability in a susceptible species, we studied the aphid life table on sorghum ÔPL 18200,Õ Sorghum
bicolor (L.) Moench. Life-table information was recorded under greenhouse conditions on the host
plants. Our results suggested that both M⫻g and energy cane are suitable hosts for S. flava. We
observed similar aphid development period on both hosts. Life-table estimates including longevity and
fecundity suggested that M⫻g is a more suitable host for the aphid than energy cane. The intrinsic
rate of increase for S. flava was lower on energy cane (0.231) than on M⫻g (0.258).
KEY WORDS biofuel, yellow sugarcane aphid, life history, energy cane, giant miscanthus
In the United States, there is a growing emphasis on will act as reservoirs of insect pests (Powell et al.
the production of two nonfood perennial biofuel 2006).
cropsÑ giant miscanthus, Miscanthus ⫻ giganteus Sipha flava (Forbes), the yellow sugarcane aphid, is
Greef et Deu ex Hodkinson et Renvoize (M⫻g here- the most widespread sucking insect pest of M⫻g.
after) and energy cane, Saccharum spp. L. (Greef and Large aphid aggregations on young plants indicate
Deuter 1993, Heaton et al. 2008, Shields and Boopathy their potential for economic impact (Bradshaw et al.
2011). M⫻g Illinois clone is a sterile hybrid with the 2010). S. flava can severely stunt young canes in the
highest harvestable biomass in a temperate zone. The Þeld, and is able to infest energy cane cultivars such as
Illinois clone has ⬇90% of the commercial M⫻g mar- L79-1002 (Van Zwaluwenburg 1918, Bischoff et al.
ket (Somerville et al. 2010, Matlaga and Davis 2013). 2008, Akbar et al. 2011, Reagan et al. 2011). Other hosts
M⫻g is also a focal species for the multistate U.S. include sorghum, Sorghum bicolor (L.) Moench;
Department of AgricultureÐFarm Service Agency wheat, Triticum aestivum L.; barley, Hordeum vulgare
(USDA-FSA) Biomass Crop Assistance Program L.; oats, Avena sativa L.; corn, Zea mays L.; rye, A.
(USDA-FSA 2011). The biofuel crop, energy cane, is hyzantina K. Koch, and Setaria spp. (Davis 1909, Starks
an interspeciÞc Saccharum hybrid with a higher Þber and Mirkes 1979, Kindler and Dalrymple 1999). S. flava
content and cold tolerance than a traditional sugar- inßicts signiÞcant necrotic damage by direct feeding
cane cultivar. It has improved biomass yield, ratooning on plant tissue. In some hosts, it is able to transmit
abilities, and vigorous growth (Beale and Long 1995, sugarcane mosaic potyvirus (Starks and Mirkes 1979,
Bischoff et al. 2008, Heaton et al. 2008, Somerville et Blackman and Eastop 1984, Breen and Teetes 1986,
al. 2010, Kim and Day 2011). To study various biotic Bradshaw et al. 2010). Host susceptibility to the aphid
factors impacting biomass production, recent studies and feeding preference for the hosts may differ with
have identiÞed several potential insect pests of M⫻g, plant species and cultivars (Starks and Mirkes 1979,
including defoliators, stem borers, and aphids (Chris- Akbar et al. 2011). For example, S. flava is more de-
tian et al. 1997, Prasifka et al. 2009, Spencer and Raghu structive in sorghum, sugarcane, wheat, and barley
2009, Bradshaw et al. 2010, Prasifka 2011). There is also than in corn and oats (Van Zwaluwenburg 1918, Starks
an increasing concern if the perennial biofuel crops and Mirkes 1979).
M⫻g and energy cane appear to be suitable hosts for
S. flava in the Þeld; however, there is no information
1 Energy Biosciences Institute, Institute for Genomic Biology, 1206
available about the aphidÕs biology on the two hosts.
W. Gregory Dr., University of Illinois, Urbana, IL 61801.
2 Corresponding author, e-mail: godshenrobert@gmail.com. S. flava biology was previously studied on sorghum,
3 Department of Crop Sciences, 1102 S. Goodwin Ave., University sugarcane, elephant grass, and several pasture grasses.
of Illinois, Urbana, IL 61801. These suggest a wide difference in host suitability
0022-0493/14/1069Ð1075$04.00/0 䉷 2014 Entomological Society of America1070 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 107, no. 3
(Kindler and Dalrymple 1999, Hentz and Nuessly sexual reproduction during or immediately after the life-
2004, Oliveira et al. 2009, Akbar et al. 2010). The table experiments. S. flava population peaks in the Þeld
speciÞc objective of our project was to study S. flava during July (Akbar et al. 2011); therefore, our life-table
biology and evaluate the host suitability of M⫻g and experiments in the greenhouse were conducted in July
energy cane. The aphid life-table estimates from this to provide favorable conditions for the aphid.
study will be useful to incorporate pest losses in bio- Life History on Mⴛg and Energy Cane in 2012. An
mass productivity models and for integrated pest man- apterous third instar of S. flava (denoted as F0 gen-
agement programs. eration) was enclosed in a small foam-ring clip cage
with outside dimensions (diameter by height) 7.3 by
1.9 cm (Catalog no. 1458, BioQuip Products Inc., Gar-
Materials and Methods
dena, CA). We used a completely randomized design,
Plants and Insects. Life-history parameters of S. and aphid cages were enclosed on leaves of the two
flava was determined on two biofuel hostsÑM⫻g Il- hosts, M⫻g and energy cane, at the rate of one cage
linois clone and energy cane ÔL 79-1002.Õ M⫻g plants per plant. All leaves selected for the experiment were
were grown individually in 1.2-liter pots at the Uni- young, undamaged, and of similar size; this was usually
versity of Illinois greenhouse using rooted plugs ob- the second or third leaf from the top of the plant. At
tained from Þeld-collected rhizomes. The rhizomes the Þrst sign of necrosis, aphid cages were transferred
were collected from the energy farm located at the from older leaves to similar unused leaves on the same
University of Illinois, Urbana Champaign. The energy plant. In each cage, the third instar (F0) became adult
cane L79-1002 was originally obtained from the Crop and reproduced to form the F1 generation. From the
Genetics and Breeding Research Unit, Tifton, GA. newly emerged F1 aphids in each cage, one Þrst instar
M⫻g and energy cane for the study was propagated was randomly selected to continue development for
using 12-cm-long mature stem cuttings. The plants the life-table study, and the remaining aphids were
were kept in a mist room until they rooted, and were discarded. The F1 generation was used for our study
then transplanted into 1.2-liter pots. Sorghum ÔPL to avoid any confounding effects of previous hosts.
18200Õ (Triumph Seed Co., Ralls, TX) was used to Development, fecundity, and longevity of S. flava
demonstrate host suitability on a susceptible host. All (F1) was studied on M⫻g and energy cane. To deter-
plants were grown in a peatÐperlite soil mix (510 mine the development period of each instar, all cages
Metro-Mix, Sun Gro Horticulture, Bellevue, WA). A were inspected daily to identify the instar based on
slow-release fertilizer, Osmocote, with 13Ð13Ð13 size. There are four instars before adult, best differ-
NÐPÐK (Scotts MiracleGro Company, Marysville, entiated by their antennal length. Therefore, length of
OH) was applied immediately after planting. Irriga- the antennae was visually correlated to instar size
tion was provided to maintain soil moisture at semi- before the experiment (Hentz and Nuessly 2004). This
saturation. All plants were grown under natural light reduced the handling time of the fragile instars during
in the greenhouse and low light conditions were sup- daily observations. After developing into reproductive
plemented using high-pressure sodium lamps with a adults, fecundity was recorded daily on both hosts
threshold of 600 Wm2. S. flava performs better at high until the F1 aphids were dead. Newly emerged Þrst
light intensity (Hentz and Nuessly 2004). Photoperiod instars (F2) were removed after daily counts to pre-
(14:10 [L:D] h) and temperature (22Ð25⬚C for 14 h, vent an increase in aphid density; therefore, the study
17Ð20⬚C for 10 h) was standardized for the experi- was density independent. The average daily fecundity
ments based on unpublished data and previous studies of S. flava (mx) on day x was calculated using equation:
(Hentz and Nuessly 2004, Oliveira et al. 2009). Pre-
liminary observations and existing literature (Miski- Bx
,
men 1970) suggest that younger plants are more Sx
suitable for S. flava development. Therefore, we con-
where Bx is the total daily fecundity of all surviving
ducted the experiments when plants were ⬇30 cm in
aphids at age x, and Sx is the total number of aphids
height and at their four-leaf stage.
surviving at this age class. Daily fecundity information
S. flava for each study was obtained from colonies
was used to construct fertility curves, and to estimate
reared on respective host plant species. For example,
maximum daily fecundity and maximum reproductive
the aphid life-table study on energy cane was initiated
age. The average lifetime fecundity and reproductive
using third instars obtained from a colony that was
period of S. flava were estimated on the hosts.
reared on energy cane for at least 90 d. S. flava colony
The cages were inspected daily on both hosts to
was established in 2011 using aphids collected from
record mortality of F1 aphids. This information was
M⫻g in the greenhouse. Occasionally, new aphids
used to construct standardized survivorship (lx) and
were introduced into each colony from M⫻g plants at
mortality curves (qx) for different development
the energy farm to maintain colony size and a diverse
stages. The parameter
gene pool. The colony was reared on 2Ð3 plants per
3.8-liter pot. A custom-made cylindrical cage (90 by 15
cm) enclosed the pot and aphids were introduced
when plants were ⬇40 cm in height. Fresh plants were
冉 冊
lx ⫽
Sx
S0
provided every week. All aphids were considered fe- is the proportion of aphids that survive to age x from
male because none of the aphids showed evidence of an initial number, S0 ; here, S0 is the initial number ofJune 2014 PALLIPPARAMBIL ET AL.: LIFE TABLE OF S. flava ON BIOFUEL CROPS 1071
Table 1. Life-table parameters (means ⴞ SEM) of S. flava on Mⴛg and energy cane
Life-table parameters M⫻g Energy cane Test statistics
First to second instar (d)* 3.23 ⫾ 0.26 1.13 ⫾ 0.13 t ⫽ 7.14; df ⫽ 1,53; P ⬍ 0.0001
First to third instar (d)* 4.94 ⫾ 0.22 3.04 ⫾ 0.14 t ⫽ 7.19; df ⫽ 1,53; P ⬍ 0.0001
First to fourth instar (d)* 6.03 ⫾ 0.21 4.75 ⫾ 0.22 t ⫽ 4.21; df ⫽ 1,53; P ⫽ 0.0001
First to adult (d) 7.06 ⫾ 0.20 6.83 ⫾ 0.20 t ⫽ 0.82; df ⫽ 1,53; P ⫽ 0.4165
Second to third (d) 1.71 ⫾ 0.12 1.92 ⫾ 0.13 t ⫽ 1.20; df ⫽ 1,53; P ⫽ 0.2342
Third to fourth (d)* 1.10 ⫾ 0.05 1.71 ⫾ 0.21 t ⫽ 2.39; df ⫽ 1,53; P ⫽ 0.0245
Fourth to adult (d)* 1.03 ⫾ 0.03 2.08 ⫾ 0.18 t ⫽ 6.75; df ⫽ 1,53; P ⬍ 0.0001
Adult to reproductive adult (d) 3.03 ⫾ 0.34 3.54 ⫾ 0.43 t ⫽ 0.96; df ⫽ 1,53; P ⫽ 0.3438
Prereproductive period (d) 10.10 ⫾ 0.36 10.38 ⫾ 0.45 t ⫽ 0.59; df ⫽ 1,53; P ⫽ 0.5610
Reproductive period (d)* 25.39 ⫾ 1.81 18.83 ⫾ 1.35 t ⫽ 2.90; df ⫽ 1,53; P ⫽ 0.0055
Lifetime fecundity* 68.35 ⫾ 4.02 37.04 ⫾ 2.95 t ⫽ 6.15; df ⫽ 1,53; P ⬍ 0.0001
Longevity (d)* 37.83 ⫾ 2.05 30.24 ⫾ 1.54 2 ⫽ 12.10; df ⫽ 1; P ⬍ 0.0005
Intrinsic rate of increase (r)* 0.258 ⫾ 0.01 0.231 ⫾ 0.01 t ⫽ 2.13; df ⫽ 1,53; P ⫽ 0.0386
Generation time (G) 13.68 ⫾ 0.49 14.08 ⫾ 0.61 t ⫽ 0.55; df ⫽ 1,53; P ⫽ 0.5822
Doubling time (Dt)* 2.77 ⫾ 0.10 3.16 ⫾ 0.17 t ⫽ 2.17; df ⫽ 1,53; P ⫽ 0.0354
Finite daily rate of increase ()* 1.30 ⫾ 0.10 1.26 ⫾ 0.06 t ⫽ 2.11; df ⫽ 1,53; P ⫽ 0.0402
Asterix (*) indicate signiÞcant difference in estimates between two hosts at ␣ ⫽ 0.05.
aphids on energy cane (S0 ⫽ 24) and M⫻g (S0 ⫽ 31). ferent aphid age groups were plotted for the two hosts.
Therefore, lx decreases from If we have estimated the intrinsic rate of increase (r),
冉冊 冉冊
aphid population growth for a discrete time interval
Sx Sx can be determined as:
1 to 0
S0 Sk
N t ⫽ N 0e rt,
over time; here, Sk is the number survived at age where Nt is the size of the population at time t, and N0 is
k 共Sk ⫽ 0) and k is the age at which all the aphids from the initial population size. Another statistic used to mea-
the same cohort died (Rockwood 2006). The mortality sure population growth is doubling time:
冉 冊
curve parameter qx is the proportion of aphids that
survived to age x, but will not survive to the next age LN共2兲
class. Dt ⫽ .
r
Population parameters estimated for S. flava on the
This parameter estimates the number of days re-
biofuel hosts include intrinsic rate of natural increase,
quired for the aphid population to double in size
Þnite rate of increase, generation time, doubling time,
(DeLoach 1974).
and age-speciÞc reproductive value. Intrinsic rate of
Results of S. flava development and population
natural increase: r ⫽ 0.738共logeMd兲/d, determines
growth parameters on both biofuel hosts were ana-
the growth of a population over time. Here, d is the
lyzed using StudentÕs t-test (␣ ⫽ 0.05; SAS Institute
number of days required for an F1 aphid to develop
2012). Longevity of the F1 aphids was analyzed using
from birth to reproductive maturity, Md is the number
the KaplanÐMeier log-rank survival test using com-
of offspring (F2) produced by F1 aphid in duration d,
plete survival data without censored values (SAS In-
and 0.738 is a correction constant (Wyatt and White
stitute 2012). Microsoft Excel (Microsoft Corporation,
1977). Finite daily rate of increase: ⫽ er, is the per
Redmond, WA) generated population growth curves
day growth rate of the aphid population (DeLoach
to compare S. flava development on M⫻g and energy
1974). Generation time: G ⫽ d/0.738, is the average
cane. Linear assumptions of normality and homosce-
time required for the S. flava population to complete
dasticity were satisÞed when required using the BoxÐ
a generation. Both reproduction and survival inßu-
Cox transformation (Box and Cox 1964).
ences G; therefore, it is different from the average
Life History on Sorghum in 2013. Our study on
development period of the aphid from Þrst instar to
biofuel crops did not include a susceptible standard.
the onset of reproduction (Laughlin 1965, Wyatt and
To address this limitation, we investigated S. flava
White 1977). Reproductive value, Vx, determines the
biology on a susceptible sorghum PL 18200 (n ⫽ 30),
age of the aphid that contributes most to the popula-
which is used to rear the aphid. M⫻g and energy cane
tion growth. For S. flava, the reproductive value at age
were not included because of resource limitations;
x was calculated using equation 1, as described by
however, experimental conditions for the two studies
Lanciani (1998):
(biofuel crops in July 2012 and sorghum in July 2013)
冘
k were similar. Aphids were inoculated on sorghum 7 d
e rx after planting. Except for two parameters, aphid life-
Vx ⫽ 䡠 e ⫺rxl xm x [1]
lx table observations on sorghum were similar to that on
x
the biofuel hosts. Fecundity and longevity of F1 aphids
Reproductive value considers fertility, survival, and were monitored for only 20 d after F2 emergence,
potential future fecundity of the aphid on its host whereas on biofuel hosts, the observations continued
(Rockwood 2006). The reproductive value of the dif- until all F1 aphids were dead. Therefore, these two1072 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 107, no. 3
Fig. 3. Relationship between percentage mortality
共qx*100兲 and development stages of S. flava on M⫻g (n ⫽ 31)
and energy cane (n ⫽ 24). Abbreviations used for x-axis, Þrst,
Fig. 1. Age-speciÞc fecundity 共mx兲 curve of S. flava on
second, third, and fourth ⫽ instars, Ad ⫽ adult, r-Ad ⫽
M⫻g (n ⫽ 31) and energy cane (n ⫽ 24).
reproductive adult, and 10Ð50 D ⫽ days after Þrst reproduc-
tion.
parameters were excluded from the calculations. Be-
cause S. flava performance on sorghum was analyzed leaf base of M⫻g and energy cane (n ⫽ 9 and 15). We
as an independent study, only reasonable comparisons compared the sample weights on both hosts using a
were made to the biofuel hosts. StudentÕs t-test (SAS Institute 2012). The percentage
Aphid Size and Morphs on Mⴛg and Energy Cane. of oviparous and alate S. flava was estimated by count-
S. flava is known to produce oviparous females in ing up to 50 aphids from similar sized third leaves of
cooler temperatures (Hentz and Nuessly 2004). The randomly selected M⫻g (n ⫽ 18) and energy cane
host preference of S. flava based on oviposition be- (n ⫽ 19). Oviparous aphids were identiÞed by the
havior is unknown. However, in general, the presence large dark green abdomen; these aphids were ran-
of oviparous and apterous aphids is positively corre- domly selected and dissected to conÞrm oviparity.
lated with superior host plant quality (Leather 1981;
Moran 1983, 1988; Powell et al. 2006). In December
2012, S. flava populations in the greenhouse included Results
a mixture of apterous, alate, oviparous, and viviparous Life History on Mⴛg and Energy Cane in 2012. The
adults of different sizes. Aphids from M⫻g and energy development period of S. flava from Þrst to second
cane were inspected according to a completely ran- instar was signiÞcantly longer (2.8⫻) on M⫻g than
domized design to determine if the size or morphs energy cane, but for subsequent instars, the period was
were biased on either host. Before sampling, aphids shorter on M⫻g (Table 1). Therefore, the total de-
were enclosed for 15Ð25 d in transparent tube cages velopment period from Þrst instar to adult (⬇7 d) was
(90 by 15 cm) Þtted on potted M⫻g and energy cane comparable on the biofuel hosts. The duration re-
(⬇70 cm in height). The biofuel hosts were grown in quired for an adult to become reproductively mature
greenhouse conditions similar to the life history study. (⬇3 d), and the prereproductive period from birth
To determine aphid size, viviparous apterous adults (⬇10 d) were comparable on the two hosts (Table 1).
(10 per plant) were randomly sampled from the third The reproductive period of S. flava, from the Þrst to
the last reproduction event or death, was signiÞcantly
longer (1.4⫻) on M⫻g than energy cane (Table 1).
Fig. 2. Age-speciÞc standardized survivorship 共lx兲 of S.
flava on M⫻g (n ⫽ 31) and energy cane (n ⫽ 24). Average
number of days required for 50% mortality of the aphid
population on the two hosts is reported as midpoints in the Fig. 4. Age-speciÞc reproductive value 共Vx兲 of S. flava on
plot. M⫻g (n ⫽ 31) and energy cane (n ⫽ 24).June 2014 PALLIPPARAMBIL ET AL.: LIFE TABLE OF S. flava ON BIOFUEL CROPS 1073
Table 2. Life-table parameters (means ⴞ SEM) of S. flava on period of 9 d (from 8 to 16 d; Fig. 4). The life-table
sorghum estimates indicated that S. flava performed signiÞ-
cantly greater on M⫻g than on energy cane.
Life-table parameters Sorghum
Life History on Sorghum in 2013. Life-table param-
First to second instar (d) 1.80 ⫾ 0.16 eters of S. flava estimated on sorghum suggest that it
First to adult (d) 5.70 ⫾ 0.13
Adult to reproductive adult (d) 1.53 ⫾ 0.16
is a suitable host. The average values are reported
Prereproductive period (d) 7.23 ⫾ 0.20 (Table 2).
Intrinsic rate of increase (r) 0.328 ⫾ 0.01 Aphid Size and Morphs on Mⴛg and Energy Cane.
Generation time (G) 9.65 ⫾ 0.24 Average weight of an aphid was signiÞcantly greater
Doubling time (Dt) 2.13 ⫾ 0.04
Finite daily rate of increase () 1.39 ⫾ 0.01
(1.5⫻) on M⫻g than energy cane. Both hosts had a
similar percentage (⬇14%) of alates (Table 3). How-
ever, only ⬇8% of the aphids on M⫻g were oviparous,
whereas oviparous aphids were absent on energy
Similarly, the average daily fecundity per surviving cane.
female 共mx兲 was higher on M⫻g than energy cane for
most of its lifetime (Fig. 1). S. flava reached its max-
imum fecundity at 13 d after becoming a reproductive
Discussion
adult, with rates of 3.87 and 3.35 per day on M⫻g and
energy cane, respectively. Aphids on M⫻g were able The life-table estimates showed that the M⫻g Illi-
to maintain the high reproduction rates for a longer nois clone and the energy cane L79-1002 are suscep-
duration. For example, there were eight events when tible hosts of S. flava. Fecundity, longevity, aphid size,
the average daily fecundity was ⬎3 per day on M⫻g, oviparity, and population growth estimates indicated
whereas on energy cane, there were only two such that M⫻g was a more suitable host than energy cane.
events (Fig. 1). The highest per day fecundity for an Our study also suggested that the biofuel hosts, even
aphid was eight and seven on M⫻g and energy cane, though susceptible, might be less suitable hosts than
respectively. The lifetime fecundity of the aphid was sorghum PL 18200.
signiÞcantly greater (1.9⫻) on M⫻g than energy cane Our results may be compared with previous life-
(Table 1). history studies of S. flava on sorghum, sugarcane, el-
S. flava (F1) was able to survive signiÞcantly longer ephant grass, and several pasture grasses (Kindler and
(1.3⫻) on M⫻g than energy cane (Table 1). The Dalrymple 1999, Hentz and Nuessly 2004, Oliveira et
longest aphid survival on M⫻g and energy cane was 59 al. 2009, Akbar et al. 2010). Based on the r values from
and 43 d, respectively. A standard survivorship curve our study, M⫻g and energy cane may be more suitable
showed that the time required for 25% mortality of S. hosts than certain cultivars of sugarcane and elephant
flava population was 29 and 23 d on M⫻g and energy grass (Nuessly 2005, Oliveira et al. 2009, Akbar et al.
cane, respectively. However, the time required for 2010). A preliminary study by Reagan et al. (2011)
75% aphid mortality was much longer on M⫻g (47 d) showed that the energy cane L79-1002 is more sus-
than energy cane (34 d), indicating that subsequent ceptible to aphids than some cultivars of sugarcane
mortality occurred faster on energy cane. The time and sorghum. Hentz and Nuessly (2004) studied S.
required for 50% mortality was 30 d on energy cane flava life table on sorghum ÔKow ChowÕ and estimated
and 38 d on M⫻g (Fig. 2). A stage-speciÞc percentage an r value of 0.314. This value is greater than our r
mortality curve showed that all aphids survived until values on the biofuel hosts, but is similar to our esti-
the Þrst reproduction event, after which, mortality mate on sorghum PL 18200. Oliveira et al. (2009)
increased. After reaching maturity, S. flava mortality indicated that the highest r value (0.12) for elephant
increased from 16 to 90% in 20 d on energy cane, and grass at temperatures 20 Ð24⬚C was ⬍0.5⫻ of the r
from 16 to 80% only after 30 d on M⫻g (Fig. 3). value (0.314) on sorghum Kow Chow by Hentz and
Intrinsic rate of increase and Þnite rate of increase Nuessly (2004), attributing the difference to host
were signiÞcantly greater, and doubling time was plant quality. A study by Kindler and Dalrymple
signiÞcantly lower on M⫻g than energy cane. The (1999) evaluated S. flava performance on eight species
average time to complete an aphid generation was of grasses and produced r values ranging from 0.136 for
similar (⬇14 d) on the two hosts (Table 1). An age- the Big Bluestem, Andropogon gerardii Vitman, to
speciÞc reproductive value curve showed that S. flava 0.235 for the Caucasian Old World bluestem, Bothri-
maintained high values (Vx ⱖ 7) on M⫻g for 23 d, ochloa caucasica (Trinius) Hubbard. Akbar et al.
when aphid age was between 7 and 29 d. On energy (2010) evaluated S. flava development on three cul-
cane, high values were observed only for a shorter tivars of sugarcane and estimated r values from 0.112
Table 3. Size and morphs (means ⴞ SEM) of S. flava on Mⴛg and energy cane
Size and morph of aphids M⫻g Energy cane Test statistics
Weight per aphid (g)* 138.02 ⫾ 11.91 93.35 ⫾ 3.74 t ⫽ 3.58; df ⫽ 1,22; P ⫽ 0.0054
Percentage of alate aphids 9.75 ⫾ 3.52 17.77 ⫾ 3.43 t ⫽ 0.93; df ⫽ 1,35; P ⫽ 0.3578
Asterix (*) indicate signiÞcant difference in estimates between two hosts at ␣ ⫽ 0.05.1074 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 107, no. 3
to 0.197. With the exception of the study by Hentz and rials. We gratefully acknowledge the Energy Biosciences
Nuessly (2004), r values from the previous studies Institute for funding this research.
were lower than our estimates on biofuel crops and
sorghum. As the experimental conditions for all these
studies (Kindler and Dalrymple 1999, Hentz and References Cited
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