Adult biology of Sialis nigripes Pictet, 1865 (Megaloptera, Sialidae)
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Boln. Asoc. esp. Ent., 26 (1-2): 2002: 59-67 ISSN: 0210-8984
Adult biology of Sialis nigripes Pictet, 1865
(Megaloptera, Sialidae)
J. M. Tierno de Figueroa & J. A. Palomino-Morales
ABSTRACT
Ceitain aspects of the adult biology of a population of Sialis nigripes were studied.
The flight period extended from the end of March to the beginning of June. The sex-ratio
was 1.58 males to Pernales. There was a decline in size over the flight period. Laboratory
studies showed the male longevity was usually shorter. Feeding was studied in both
sexes although gut contents were negligible in the male, whereas in the female an indis-
tinct mass in the gut may correspond to the male spermatophore. In relation to reproduc-
tive behaviour, the duration of spermatophore iransmission was quantified. The position
adopted during spermatophore transmission was similar to that of other Siaiis species.
Key Words: Megaloptera, Sialis nigripes, Phenology, Biometry, Feeding, Repro-
ductive behaviour, Southern Spain.
RESUMEN
Biología del adulto de Sialis nigripes Pictet, 1865 (Megaloptera, Sialidae)
Se estudian diversos aspectos de la biología de una población de Sialis nigripes del
Sur de la Península Ibérica. El período de vuelo se extiende desde finales de marzo
hasta principios de junio. La sex-ratio es de 1,58 machos con respecto a hembras. Se
observa una disminución en tamaño conforme avanza el período de vuelo. Los estudios
en laboratorio muestran una longevidad generalmente menor en los machos. La alimen-
tación, estudiada en ambos sexos, muestra un contenido inapreciable en machos y una
masa indistinguible en el digestivo de las hembras que debe corresponder al espermató-
foro del macho. En relación con el comportamiento reproductor, se cuantifica
la duración de la transmisión del espermatóforo. La posición adoptada durante la trans-
misión del espermatóforo es similar a la presentada por otras especies de Sialis.
Palabras clave: Megaloptera, Sialis nigripes, Fenología, Biometría, Alimentación,
Comportamiento reproductor, Sur de España.
ÍNTRODUCTION
Alderflies (Sialidae) represent an insect group with only six species on the Euro-
60 J. M. Tierno de Figueroa & J. A. Palomino-Morales
pean Continent; of these, three [Sialis lutada (Linnaeus, 1758), S. fuliginosa Pictet, 1836
and S. nigripes Pictet, 1865] are widely distributed in Northern, Central and Southern
Europe, including the British Isles (MEINANDER, 1996; MONSERRAT, 1984). The general
biology of S. lutada has been studied, but comparatively little is known about S. fuligi-
nosa and almost nothing about S. nigripes (ELIJOTT, 1996).
In the Iberian Península, no studies are available on the adult biology of the Siali-
dae, although recently the biotic and abiotic factors related with the distribution of S. ni-
gripes larvae (ZAMORA-MuÑoz et al., 1999) and eggs and clutches of the same species
(TIERNO DE FIGUEROA & PALOMINO-MORALES, 2001) have been studied. The present
study increase the knowledge of the little-known group, Megaloptera, concerning its re-
production and Other aspects of its adult life. The lack of studies is especially pronounced
in the South of Europe, where the populations can present dynamics partí a I ly different
from those shown in more northern latitudes. Thus, an in-depth study of this species is
needed both in field as well as in the laboratory.
MATERIAL AND METHODS
The study was conducted in the Turberas del Padul (Granada, Spain), one of the
most ímportant wetlands of the south-eastern Iberian Península, located on the western
endof the Sierra Nevada Mountains a t a n allitude of 740 m.a.s.l. (37°T N, 3°36'W).
Along a channel from the Turberas de Padul the vegetation of each bank was sam-
pled in a 150-metre transect. The vegetation was composed predominantly of Phragmites
ausíralis and Scirpits holoschoenus, interspersed with wild Poaceae. Approximately one
metre from the bank, cereal crops were under cultivation. Samples were taken simulta-
neously but independently by two people along the fixed transect near the banks; all the
S. nigripes individuáis were colíected by hand. This method, direct collection by hand,
is more effective than the use of a net because specimens have little ability to escape and
sometimos simply fall on the ground where they are easily collected by hand.
The samples (12 in total) were with a periodicity between 4 and 10 days, from
19/March/99 to 17/June/99. Previous and subsequent point samples showed the absence
of adults, thus ensuring that the flight period of the species was within this interval.
In each samples, all the Sialis nigripes individuáis collected were placed in dram
bottles and transported to the laboratory. All the individuáis were sexed live to calcúlate
the sex-ratio. This ratio was checked with the help of a non-parametric chi2 test (SiEGEL
&CASTELLAN, 1988).
For the mortality study, all the specimens from six samplings [3 (5/4/99); 4 (9/4/99);
6 (29/4/99); 7 (7/5/99); 8 (13/5/99) and 10 (28/5/99)] were brought alive to laboratory
and kept in a 27x19x5.5 cm box with transparent upper part and with plañí material,
leaves and small branches inside, at room temperature and under natural light. All the
dead individuáis were removed each day and represented on the curves. Nevertheless,
since the individuáis were collected as adults in the field, we did not know the exact age
of the specimens when captured; henee we could not deduce the absolute longevity.
From each sampling, 10 males and 10 females were randomly taken for measure-
ment (except for those in which the number of individuáis collected was lower, where-
upon the máximum number possible was measured). To establish clear morphological
points of reference, we took the fémur measurement as an indicator of the size, being this
a rigid, fíat structure (thereby avoiding problems related to curvature). Measuremenls
Adult biology of Sialis nigripes 61
were taken with the micrometer of Olympus binocular microscope with a magnification
of 30x. The data were used to study the possible size variations over the flight period.
The statistical tests used were the Kolmogorov-Smirnov normality test and the Pearson
correlation coefficient (SOKAL & ROHLF, 1995).
Concerning adult feeding, we proceeded as in TIERNO DE FIGUEROA et al. (1998) and
TIERNO DE FIGUEROA & SÁNCHEZ-ÜRTEGA (1999), employing a transparency method for
sudes with Hertwig's liquid (Bello, pers. comm.), a variation of Hoyer's liquid. All the
individuáis collected in sample 5 (19/April/99) (22 males and 7 females) plus 2 females
from previous collections in the same área were analysed. They were placed in alcohol
directly in the field, and later in Hertwig's liquid in the laboratory for 10 hours at 65°C
in an oven. Afterwards, the specimens were mounted on slides and sealed with enamel.
To study the gut contents, we used an Oxford Trade microscope with a magnification of
60x, I50xand600x.
To study the reproductive behaviour of this species, we made field and laboratory
observations. In the laboratory, some individuáis, males and females, were put in a box,
27x19x5,5 cm, with a transparent glass on the upper part and with vegetal material,
leaves and small branches, inside.
The data were analysed with the Statistica package for Windows 4.0 (1993).
RESULTS
1. Phenology
The flight period found for Sialis nigripes in the study área spans from the end of
March to the beginning of June (29/March/99 to 7/June/99), but almost all the captures
were concentrated in the months of April and May, and therefore this species can be con-
sidered a spring species. Figure 1 lists all the captures over the flight period.
IV/29 V/7 V/13 V/21
Sampling dates
Figura 1. Flighl period of S. nigripes (males, females and total individuáis) in the study área.
Figure 1. Período de vuelo de S. nigripes (machos, hembras y total de individuos) en el área de estudio.
62 J. M. Tierno de Figueroa & J. A. Palomino-Morales
The sex-ratio was 61.22% males and 38.78% females (1.58males/females) (chi2= 13.236;
p
Adult biology of Sialis nigripes 63
2. Biometry
S. nigripes females are larger than the males (around 10.6% longer in terms of mean
fémur length).
In males as well as in females of S. nigripes, the size, measured as mean length of the
third-leg femurs, declined during the emergence period (K-S d= 0.10; p >0.20; N= 75,
r= -0.55, p 0.20; N= 73, r= -0.55, p
64 J. M. Tierno de Figueroa & J. A. Palomino-Morales
navia and Denmark (MEINANDER, 1996). In the Iberian Península, isolated captures of
this species are known from the end of March to the beginning of August (MONSERRAT,
1984), and particularly in Granada province, we collected some adults in the mid-June
1999 in the Sierra de Huétor, at 1200 m.a.s.l., where, for the high altitude, the flight pe-
riod can be delayed. These differences in phenology can be caused by temperatura vari-
ations which, as reported for aquatic insects in general (SWEENEY, 1984) and in the case
of another Sialidae species (ELLIOTT, 1996), usually cause earlier emergence in locations
with higher temperatures that correspond to lower altitudes and latitudes.
In figure 1 a strong decline in the collected individuáis in sample 6 (29/April/99)
was observed, and this could be explained by the climatic conditions of that day (clouds,
light rain and wind) that would cause a general inactivity of the individuáis and the fact
that they were hidden into the vegetation and were less vulnerable to be collected.
Although the total sex-ratio was 1.58 males/females, figure 2 shows that the higher
sex-ratio for males was more pronounced in the first half of the flight period but de-
creased in the second half, and reversing in the last sample, perhaps indicating protandry.
A special case was again sample 6, in which the number of females collected was simi-
lar to other samples, in contrast with the pronounced decline in the number of males, pos-
sibly due to greater climatic sensibility of males. We did not ascertain whether the dif-
ference in the total male and female percentage was caused by different mortal i ty rate
during the embryonic, larval or adult stages, or by a differential production of the two
sexes with genetic basis, as it has been demonstrated in certain díptera (CLEMENT, 1963;
HAMILTON, 1967).
Literature data show that Sialis species have a very short adult life, a week or rarely
more man two (ELLIOTT, 1996; HAYASHT, 1999), similar to that found in our study of S.
nigripes. However there is no Information concerning sex differences in longevity in
Megaloptera ñor about variation of individual longevity through the emergence period.
Our data showed that mortality is higher in males and decreases, perhaps related to the
high temperatures, as the emergence period advances (Fig. 3).
2. Biometry
As reported in Sialidae (ELLIOTT, 1996), S. nigripes females pro ved larger man the
males. This size difference could be a consequence, as pointed by MOREIRA &
PECKARSKY (1994) for another aquatic insect group (Plecoptera), of different selective
pressures favouring greater female size, in relation to higher fecundity, and a smaller
male size to diminish predation risk. In fact, we studied the number of eggs from females
collected in the field and dissected in the laboratory, and we found a tendency to a high-
er number in bigger females. Nevertheless, since we do not know if the females had
oviposited before being capturad, we can not draw significant conclusions.
Severa] aquatic insect groups show a general decrease in individual size, at least in
species from áreas with certain seasonality, as the emergence period advances (MOREIRA
& PECKARSKY, 1994; SWEENEY et a!., 1995; COLEANTES & MARTÍNEZ-ORTEGA, 1997).
However, at least in some orders, this trend has rarely been statistically analysed, as hap-
pens in Plecoptera (FROEHLICH, 1990; MOREIRA & PECKARSKY, 1994), or there are no
works available at all. as happens in Megaloptera. Our study supports the first evidence
for the order Megaloptera that the size declines during the emergence period. A possible
explanation for this decrease in adult size along the emergence period, may be that, as in
other groups (Knoo, 1964; SWEENEY et al., 1995), the individuáis with adequate devel-
opment (and adequate size) emerge at the beginning of the flight period, when the envi-
Adult biology of Sialis nígripes 65
ronmentaJ conditions are optimal, whereas the individuáis with deficient size (from ge-
netic or other causes) musí emerge later under the risk of lower reproductive success.
3. Feeding
Data on adult feeding of the different Sialis species remain limited and contradicto-
ry at present; although some studies pointed out (from indirect evidence) that these in-
sects feed on pollen and néctar, no such contení has been found in the guts (ELLIOTT,
1996). Thus, in the case of S. nígripes, we studied the possible presence of some type of
solid food inside the gut both in males and in females. The results showed that male prob-
ably does not feed at adult stage, although a small amount of detritus was found in two
individuáis. However, this does not necessarily indícate solid feeding in the adult stage.
The origin of these remains is unknown, but possibly they were ingested accidentally
when the individuáis were drinking; in fact in laboratory other Sialis species take in fin-
ids (PRÍTCHARD & LEISCHNER, 1973).
The ingestión of the male spermatophore implies a considerable additional energy
source for the female. The small amount of ascomycete spores, detritus and some pollen
grains found in the female gut, could have been ingested accidentally during drinking, as
happens in the males, or when females ingested the spermatophore.
4. Reproductive behaviour
Vibrational communication has been described in Sialis hitaría and S. fuliginosa by
RUPPRECHT (1975, 1983). This author has recorded the vibrational calis of some Euro-
pean species of the genus Sialis, including S. nígripes (RUPPRECHT, pers. comm.). The vi-
brations observed in some females in our study probably correspond to this kind of in-
tersexual communication.
Spermatophore transmission in S. nígripes is similar to that described for S. hitaría
(ELLIOTT, 1996). Moreover, the spermatophore transmission time is very short, similar to
that of other Sialis species, i. e. between 0.5 and 2 minutes (HAYASHI, 1999).
S. nígripes male does not guard the spermatophore that attaches to the female (post-
mating guarding), possibly because the time needed to empty the spermatophore is very
short (HAYASHI, 1999).
We found that the female can mate more than once, and this is probably more re-
lated to the energy profit obtained from ingesting of the spermatophores than with the
need for more sperm to fértil ise the eggs, as was demonstrated in another Megaloptera
species of the family Corydalidae, Protothermes granáis, (HAYASHI, 1998). Moreover,
more than one mating can contribute to increased genetic diversity of the offspring or
compénsate for a previous mating with a lower-quality male.
We were not able to compare the S. nígripes spermatophore described in this work
with that of other European Sialidae species because there is no information available on
the size and shape of the spermatophore (HAYASHI, 1992). However Corydalidae sper-
matophores are bigger than the Sialidae ones (HAYASHI, 1992) and on Asiatic Sialidae
spermatophores are similar in size and shape ío S. nígripes (HAYASHI, 1999).
The unproductive mating attempts in insects have been frequently reported in the liter-
ature (THORNHILL & ALCOCK, 1983; TIERNO DE FIGUEROA, 2000). In nature, the number of
mistaken mating attempts must be lower than in the laboratory, because vibrational calis ancl
other types of communication and low densities of individuáis must favour the encounter of
males with females and must discourage with the encounter between males, respectively.
66 J. M. Tierno de Fis;ueroa & J. A. Palomino-Morales
ACKNOWLEDGEMENTS
We are grateful to D. Nesbit and Dr. P. Christie for advice on the English and Dr.
Fochetti for his comments.
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Facha de recepción: 5 diciembre 200!
Fecha de aceptación: 8 febrero 2002
José M a n u e l T i e r n o de F i g u c r o a José A n t o n i o P a l o m i n o - M o r a l e s .
Departamento de Biología Animal y Ecología. Facultad de Ciencias.
Universidad de Granada. 18071. Granada. Spain.You can also read
