DYNAMICAL EFFECTS OF HOST-FEEDING IN PARASITOIDS

1. Synovigenic parasitoids emerge as adults with fewer mature eggs tha n they can ultimately lay. They need to feed on host fluid or tissue t o gain protein in order to mature additional eggs. The decision to hos t-feed or parasitize an encountered host depends in part on the curren t number of mature eggs that the parasitoid is carrying (its egg load) , with host-feeding more likely at low egg loads. Protein gained from host-feeding may also be used for maintenance and to prolong the life of the adult parasitoid. Host-feeding often renders a host individual unsuitable for subsequent parasitism and thus can cause substantial ho st mortality. We investigated the dynamical effects of several aspects of host-feeding and synovigeny. 2. We found that host-feeding per se had no effect on the stability of interacting host and parasitoid popu lations. In addition, the decision to host-feed or parasitize an encou ntered host, based on the female parasitoid's current egg load, had no effect on stability. 3. The host and parasitoid equilibria were stabi lized by a parasitoid mortality rate that was a decreasing function of egg load. 4. A drain of egg material gained from host-feeding for use in maintenance destabilized the equilibria, provided that either the parasitoid death rate or birth rate (via the probability of host-feedi ng given an attack) depended on egg load. An input of protein that cou ld be used to produce eggs from a source other than the host had a sta bilizing effect. 5. Results 3 and 4 arose in models that categorized t he adult female parasitoid population according to each individual's e gg load, and a female's behaviour was determined by her egg load. Anal ogous, but unstructured, models in which females responded to the mean population egg load gave results that were identical to the structure d models, except when parasitoid survival depended on egg load.