The Influence of Competition between Foragers on Clutch Size Decisions in Insect Parasitoids

The effect of competition between ovipositing females on their clutch size decisions is studied in parasitoid insects. The effect of this competition depends on whether the competition between parasitoid larvae within a host is contest (solitary parasitoids) or scramble competition (gregarious parasitoids). For gregarious parasitoids, a decreasing clutch size with increasing competition between females is predicted while for solitary parasitoids an increase is predicted. These predictions were tested using the gregarious parasitoidAphaereta minuta(M. E. Visser, 1996,Behav. Ecol.7,109–114) and the solitary parasitoidComperiella bifasciata(J. A. Rosenheim and D. Hongkham, 1996,Anim. Behav.51,841–852). Parasitoids were either kept alone or in groups before the experiments, in which they were introduced singly into a patch containing unparasitized hosts. In the experiment withA. minuta,females kept together before the experiment laid smaller clutches than females kept alone. InC. bifasciata,the clutch size laid by females kept together was larger than that of females kept alone. Thus, both predictions were supported.