Seminarios IHSM La Mayora - Eric Wajnberg INRA (Francia)

Optimal patch exploitation time in insect parasitoids: From ultimate predictions to proximate patch-leaving mechanisms The Marginal Value Theorem predicts the optimal time an animal should invest in exploiting patches of resources in the environment. This model was originally published in 1976 by E. Charnov, and, since then, an increasing number of works demonstrated that the corresponding theoretical predictions are usually accurately followed by animals from different species, including insect parasitoids. However, animals are not expected to calculate optimal behaviors in the way suggested by optimization models. They would be more likely expected to use proximate behavioral rules that should be both simple and robust. After a rapid presentation of insect parasitoids and their potential use in controlling pests on crops, the talk will present this theoretical framework and the associated assumptions. Then, both theoretical and experimental works will be presented, trying to see what parasitoid females should do when several assumptions of the original Charnov models are relaxed, leading to more realistic situations. More accurately, the results presented will address two important issues: (1) Since parasitoid wasps are usually exploiting patches of hosts by walking, a model simulating the intra-patch movement decisions of wasp females exploiting patches with different host abundances and distributions will be presented. The model parameters were optimized in the different environments by means of a genetic algorithm. Results indicate that simple modifications of the walking pattern of the foraging animals when hosts are discovered can lead to patch residence times that appear consistent with optimal predictions. (2) also, a stochastic dynamic programming model will be presented to predict the optimal patch residence time when animals are short-lived (a feature that is not taken into account in the literature), and experiment will be presented to show how real animals are following such predictions.