Factors affecting body size and fat content in a digger wasp

Abstract

Body size is one of the most important life history traits. In mass-provisioning solitary Hymenoptera, the maximum attainable adult size is not under the control of the larva but is limited by the amount of resources provided by the mother. I investigated the effect of the amount of different maternal resources and potentially interfering abiotic (temperature) and biotic (fungus infestation) factors on offspring body size and fat reserves in a solitary digger wasp, the European beewolf, Philanthus triangulum F. (Hymenoptera, Sphecidae). Females provide different resources for their progeny that might influence progeny size (egg, brood cell, and paralysed honey-bees as food). The number of bees provisioned explained the largest proportion of variation in cocoon length. With an increasing number of bees (one to four), progeny gained less weight per bee. Relative fat content increased with size. With a given number of bees, males were smaller than females. The duration of the feeding period was independent of the number of bees in a brood cell but decreased with increasing ambient temperatures (20, 25, 30°C). Cocoon size was influenced by temperature but the effect was not uniform. Cocoons from brood cells containing two and three bees were larger at 25°C than at 20°C; those at 30°C did not differ from those at either lower temperature. However, in brood cells containing one bee, cocoon length was independent of temperature. Sublethal levels of fungus infestation may have a small negative effect on cocoon size. Different temperatures during hibernation (8 vs 13°C) did not affect the size or fat content of emerging adults. These results on a mass-provisioning hunting wasp are compared with the well-studied herbivorous insects.

Female Life Span and Fertility Are Increased by the Ejaculates of Preferred Males

“…Such negative correlations between temperature and development time have been described for numerous insect species (Ratte 1984) and have also been found in earlier studies on P. triangulum (Strohm 2000). This effect is generally ascribed to the temperaturedependence of basal biochemical processes (Schmidt-Nielsen 1999).…”

“…Generally, a short development time is advantageous, because it might reduce the mortality risk in the vulnerable larval stage (Sibly and Calow 1986). Selection for a fast development is likely to be particularly strong in P. triangulum, because the larvae are exposed to a high density of pathogenic microorganisms in their subterranean brood cells and, thus, face a high risk of bacterial or fungal infestation (Strohm andLinsenmair 1998, 2001;Kaltenpoth et al 2005;. P. triangulum females in Central Europe strongly prefer areas with favourable climatic conditions (i.e.…”

“…triangulum are solitary digger wasps that live in warm and sandy areas (Strohm and Linsenmair 1995). Females excavate a nest burrow with several separate brood cells, each of which is provisioned with one to five paralysed honeybees (Apis mellifera) as food for the developing larva (Strohm and Linsenmair 1995, 2000. To prevent fungal infestation in the warm and humid brood cell, the prey is preserved by the females by embalmment with a gland secretion .…”

Estimating body size in apoid wasps: the significance of linear variables in a morphologically diverse taxon (Hymenoptera, Apoidea)

“…accordance with the use of head width as an estimator of body size in numerous ecological and behavioural studies on the European beewolve, Philanthus triangulum (e.g., Strohm & Lechner 2000). Strohm (2000) measured head width, dry weight, and fresh weight of newly emerged Philanthus triangulum hibernated at different temperatures to explore factors affecting total body size. His data correspond nicely to those of the male P. triangulum included in this study (Strohm's data (n ¼ 16): dry weight 14.2 AE 6.2 mg, head width 3.53 AE 0.39 mm; our data: dry weight 13.5 mg, head width 3.5 mm).…”

“…Individual body mass also depends on the physiological condition (e.g., limited or unlimited food ressources availabe), the reproductive state (e.g., number of mature and immature eggs in the female ovaries; see McCorquodale 1990), and numerous other factors. In insects, many of these problems can be solved by using "standardized" individuals, that is, individuals reared under standardized laboratory conditions and weighed at a standardized moment, preferably immediately after hatching from the pupa (e.g., Strohm 2000).…”