Optimal time allocation in parasitic wasps searching for hosts and food

Many species of parasitic wasp feed on sugar sources such as nectar and honeydew in order to replenish their energy reserves and so extend their life expectancy, which is often correlated with higher reproductive success. Recent research suggests that carbohydrates are also a key component in flight fuel in such insects. The importance of sugar in fuelling locomotion suggests location of sugar-rich food may be more important in parasitoid foraging behaviour than has previously been assumed. If sugar sources and hosts are separated in space, parasitoids have to allocate their time between sugar-searching and host-searching. Using a stochastic dynamic programming model we predict optimal time allocation decisions of parasitoids. Although the model was parameterized using data for Cotesia rubecula, the sensitivity analysis shows that the model predictions are applicable to many parasitoid wasp species. The key prediction of the model is that parasitoids should always search for food if energy reserves drop to low levels, even if the probability of finding food and the average food reward are small. This is in stark contrast to an alternative model proposed by Sirot and Bernstein (1996) which suggests parasitoids should never search for food if food availability is low.