Time sharing between host searching and food searching in parasitoids: State-dependent optimal strategies

By varying the time spent searching for food, parasitoids modify their expected lifespan, and therefore their total lifetime reproductive success. Using a stochastic dynamic approach, we define the best choice between searching for food and searching for hosts as a function of the state of the parasitoid and the availability of food when hosts and food are found in different parts of the environment. A first model deals with the influence of food availability and survivorship conditions on the behavior of a single parasitoid. Our results suggest that under conditions of very low food availability, parasitoids should never search for food. When food availability is moderate, parasitoids should not wait until their reserves are low before searching for food. When food is abundant and survivorship is independent of food consumption, parasitoids should search for food only when their reserves are almost exhausted. They should not wait so long if survivorship depends on the energy reserves. By finding the state-dependent ideal free distribution for a population of parasitoids, we are able to predict their distribution between the feeding area and the host living area at equilibrium. The proportion of parasitoids in each area is altered by the number of competitors and interference. Finally, the model predicts that optimal time sharing between food searching and host searching may promote the stability of the host-parasitoid system.