OBSERVATIONS ON THE PREY AND NEST CLUSTERS OF PODALONIA VALIDA (CRESSON) (HYMENOPTERA : SPHECIDAE)

4 Pages·1999·1.9 MB·

by  K M O'neill

PROC. ENTOMOL. SOC. WASH.
101(2), 1999, pp. 312-315
OBSERVATIONS ON THE PREY AND NEST CLUSTERS OF PODALONIA
VALIDA (CRESSON) (HYMENOPTERA: SPHECIDAE)
Kelvin M. O'Neill and Howard E. Evans
(KMO) Department of Entomology, Montana State University, Bozeman, MT 59717,
U.S.A. (e-mail: [email protected]); (HEE) Department ofEntomology, Colorado State
CO
University, Fort Collins, 80523, U.S.A.
—
Abstract. In northern Colorado, Podalonia valida preyed upon mature larvae of the
saltmarsh caterpillar, Estigmene acrea (Drury), the same prey it uses in Arizona. Prey
were deposited in shallow, single-celled nests that occurred within clusters probably pro-
visioned by single females. Because females forage for abundant nearby prey, stock each
nest cell with a single caterpillar, and dig simple nests in a localized area, they have the
potential to provision multiple nests over short time periods. Several observations are
consistent with this hypothesis. First, within clusters of nest cells, there was a high degree
of synchrony in developmental stages of the wasps, suggesting that eggs were laid in
quick succession. Second, dissections showed that female P. valida carry more mature
eggs in their ovaries than is typical for non-parasitoid aculeate wasps.
Key Words: Digger wasp, Sphecidae, nesting behavior, egg size, Estigmene acrea, salt-
marsh cateipillar, Arctiidae
Wasps of the genus Podalonia dig short we present results of our observations of
burrows terminating in a cell provisioned the nesting behavior and prey of P. valida
with a single prey (Bohart and Menke in northern Colorado and compare our find-
1976). Podalonia luctuosa (Smith) ings to those of Steiner, who concentrated
(O'Brien and Kurczewski 1982), Podalonia on the hunting and territorial behavior of
robiista (Cresson) (Kurczewski et al. 1992), females.
and Podalonia argentifrons (Cresson)
Methods
(O'Brien 1983) restrict themselves to cut-
worms (Noctuidae), but may take a variety We studied P. valida females at the Paw-
of species at any one site. Similarly, Po- nee National Grasslands in northern Weld
dalonia occidentalis Murray apparently Co., Colorado, from 12 July to 13 August
prey solely on tent caterpillars (Lasiocam- 1984. The site was situated along a sandy,
pidae: Malacosoma) (Evans 1987) and Po- little-used road that passed through prairie
dalonia valida (Cresson) limit themselves consisting of grasses mixed with several
to arctiid moth cateipillars. Steiner (1974, common forbs, notably white sweetclover
1975) found P. valida specializing on salt- (Melilotus alba Desr.) and sunflower (He-
marsh caterpillars {Estigmene acrea (Dru- lianthus spp.).
ry)) in southern Arizona, whereas Rust et
Results and Discussion
al. (1985) found two female P. valida tak-
ing Apantesis proxima (Guerin-Meneville) Our 64 prey records indicate that P. val-
on San Clemente Island, California. Here, ida preyed exclusively on mature larvae of
VOLUME NUMBER
101, 2 313
the saltmarsh caterpillar Estigmene acrea be clustered. In 2 of our 7 excavations of
(Drury) (Arctiidae), the same species used recently completed nests, we unearthedjust
by this wasp in Arizona (Steiner 1974). The a single cell, but in the others, we found
prey ofP. valida, which were probably tak- clusters of 8, 15, 16, 18, and 27 cells within
en on their host plants (white sweetclover), areas no more than 0.25 m-. Some cells
were carried in the mandibles as females were separated by as little as 5 cm, but were
walked forward straddling the prey. One fe- definitely parts of different nests. Clusters
m
male carried a caterpillar at least 10 be- of nest cells were well-separated from one
fore reaching her nest. Prey-carrying fe- another and each was apparently used ex-
males occasionally stopped and cached clusively by a single female, who vigorous-
their prey —5 cm above the soil surface on ly attacking conspecific females intruding
small plants, where they were left for sev- upon their nest cluster in interactions that
eral minutes while females searched for included bouts of grappling between the
their nests. combatants. Similar interactions between P.
Unlike other species of Podalonia, P. valida females have been described in de-
valida dig nests before hunting (Steiner tail by Steiner (1975).
1974, 1975). Each nest at our site consisted The contents of unparasitized and non-
of a short, oblique burrow about 1 cm in moldy P. valida cells within clusters sug-
diameter, terminating in a single 1 X 3 cm gest that, if a single female was responsible
cell situated 3-5 cm beneath the soil surface for all of the cells, some were provisioned
(N = 7). Typically, when digging the nest, during short time intervals. For example, in
a female backed out 5-10 cm from the bur- the cluster of 15 cells, 5 had prey with wasp
row entrance and scraped soil backwards eggs, 3 had prey with small wasp larvae,
with her forelegs, while elevating her ab- and 1 had a large wasp larva. In the cluster
domen, flicking her wings rapidly, and of7 cells, all had prey with unhatched eggs.
buzzing loudly. Upon returning to her nest Similarly, the cluster of 18 cells included 7
with prey, a female dropped it at the en- prey with wasp eggs and 7 with small wasp
trance, cleared the burrow, and pulled the larvae, and the cluster of 16 cells contained
prey inside while moving backwards. After 7 with eggs or small larvae.
several minutes inside the nest, during The potential ability of P. valida fe-
which time she laid an egg on the prey, the males to provision multiple nests in rapid
female emerged and permanently closed the succession may be possible because they
bunow by scraping in soil from the edge of 1) forage for abundant prey nearby. 2)
the burrow and placing lumps of soil or stock each cell with a single prey, and 3)
pebbles in the hole. She then tamped the dig simple, shallow nests without search-
loose soil with her head (mandibles wide ing widely for successive nesting sites.
open) or with a lump ofsoil which was held This strategy may allow them to exploit a
in the mandibles and which broke up due single developmental stage ofa single prey
to the impact. The entire sequence between species that is available forjust a brief pe-
entering the hole with prey and completing riod during the summer However, the rap-
closure typically took about 4 minutes. id stocking of multiple nests would also
These observations are in accord with require that a female produce the requisite
those of Steiner (1974, 1975), who found numbers of eggs. Typically, female sphe-
that individual females provisioned series cids carry no more than two mature eggs
of single-celled nests within small patches at a time, although they have three ovari-
of bare soil sometimes no more than 60 cm oles in each ovary (Iwata 1964, O'Neill
across. Although we did not observe indi- 1985). Nevertheless, the three P. valida fe-
vidually marked females over prolonged males that we captured within minutes of
periods, we also found that cells tended to their laying eggs had 3, 5, and 6 mature
314 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON
(or nearly mature) oocytes still in their nest provisioning species that spend con-
ovaries. Thus, the latter female had been siderable time and energy on each off-
carrying seven well-developed oocytesjust spring. This strategy is facilitated by the
prior to capture and had one ovariole with greater number of mature eggs they carry
two mature oocytes. In Iwata's extensive and, perhaps, by shorter periods ofsearch-
survey of the ovaries of solitary aculeate ing for potential nest sites once nesting
wasps, only parasitoid sphecids ofthe gen- has begun.
era Larra (with up to 21 mature oocytes)
Acknowledgments
and Chlorion (with up to 10) carried more
mature eggs than the maximum for P. val- We thank Patricia Denke, Wendell Mor-
ida. Such high levels of short-term fecun- rill, Mark O'Brien, and Catherine Seibert
dity (for a digger wasp), however, may be for commenting on the manuscript and N.
achieved at the cost of producing smaller Woodley (Systematic Entomology Labora-
eggs. The mature oocytes of P. valida tory, USDA, Washington, DC) for deter-
mm
ranged in length from 2.6-3.1 in mination of the tachinid fly. The work was
length and one egg found on prey was 2.9 supported by the National Science Foun-
mm
long. In contrast, in the similarly-sized dation, the Colorado Agricultural Experi-
but less fecund wasp Philcmthus hicinctus ment Station, and and the Montana Agri-
(Mickel), mature oocytes and newly laid cultural Experiment Station.
mm
eggs ranged as high as 5.4 in length,
and had perhaps 3-4 times the volume of Literature Cited
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quinqiiespinosus (Say) and Philanthus American Tachinidae (Diptera). Miscellaneous
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ida, although they are both much smaller culture, 860 pp.
Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps
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fly puparia 0.5-1.0 cm below the cell, Evans, H. E. 1987. Observationson the prey and nests
which in each case-contained the remains of Podalonia occidentalis Murray (Hymcnoptera:
of a single saltmarsh caterpillar. One pu- Sphecidae). Pan-Pacific Entomologist 63: 130-
134.
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known parasitoid of E. acrea (Arnaud boo carpenter bees. Nature and Life in .Southeast
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Our observations complement those of havior of Podalonia argentifrons. Southwestern
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VOLUME NUMBER
101, 2 315
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