Energy dynamics in a parasitoid foraging in the wild

Abstract

Summary 1.Although parasitoids are used widely as a biological models for understanding the evolution of animal behaviour, most studies have been constrained to the laboratory. The dearth of field studies has been compounded by the almost complete ignorance of the physiological parameters involved in foraging and dispersal, in particular of the energetic constraints imposed by resource limitation. 2. We estimated the dynamics of carbohydrates and lipids reserves of Venturia canescen s (Gravenhorst) females by releasing individuals of known nutritional status in a natural environment and recapturing them using host-containing traps. The recapture rate was around 30%. These results were compared with the reserves of caged animals kept under different experimental conditions (freshly emerged, starved to death, fed ad libitum and partially starved). Wild animals were also sampled in order to estimate the resource levels of the local population. 3. The results show that: (i) wasps are able to maintain a nearly constant level of energy over an extended foraging period; (ii) V. canescens takes sugars in the field; and (iii) the lipid reserves accumulated during the larval life may be limiting as lipogenesis does not take place in adults even under conditions of high sugar availability. 4. These results demonstrate that wasps can forage for hosts and food and disperse in this habitat for hours and days without running into a severe risk of energy limitation.

Loss of lipid synthesis as an evolutionary consequence of a parasitic lifestyle

“…Parasitoids can also economize on lipid use if acute energy requirements can be met by regular ingestion of sugars through feeding on nectar, honeydew, or carbohydrate-rich oviposition substrates (30). For example, in the parasitoid Venturia canescens, nectar feeding occurs frequently in the field, postponing the moment of lipid depletion despite relatively low capital lipid levels (31).…”

Honeydew as a food source for natural enemies: Making the best of a bad meal?

“…Other studies found a relatively high incidence of sugar feeding in parasitoids collected from nectar-poor fields and concluded that parasitoids must have exploited alternative sugar sources, most likely honeydew (Casas et al, 2003;Lee and Heimpel, 2003;Lee et al, 2006). Although honeydew may be an important food source for biological control agents in agro-ecosystems, we still have limited quantitative data on the use of honeydew by parasitoids and predators.…”

The nutritional value of aphid honeydew for non-aphid parasitoids

“…Field caught parasitoids commonly contain honeydew sugars (Wa¨ckers & Steppuhn, 2003) and Casas, Driessen, Mandon, Wielaard, Desouhant, van Alphen et al (2003) showed that wasps can forage within a habitat for days in a situation where homopteran honeydew seems to be the only food source available. This suggests that this food source can be exploited in the field to enhance the efficacy of biological control agents.…”