ADAPTIVE SUPERPARASITISM AND HOST-PARASITOID DYNAMICS

We consider a host-solitary parasitoid system with three categories of individuals: parasitoids, healthy hosts and parasitized hosts. Parasi toids are assumed to discriminate perfectly between the two kinds of h osts and they can reject those which are already parasitized. If paras itoids systematically accept or reject superparasitism or behave rando mly, the system is always unstable. Using an optimal foraging model, w e determine the behavior of parasitoids which leads to maximization of the instantaneous reproductive rate. When following this adaptive dec ision rule, parasitoids accept or refuse superparasitism according to the densities of both healthy and parasitized hosts. We study the dyna mics of the system when parasitoids follow the optimal rule and show t hat under certain conditions it possesses a locally stable equilibrium point. In addition, our model predicts that at equilibrium parasitoid s show partial preferences for superparasitism. (C) 1997 Society for M athematical Biology