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 co mpetition depends on whether the competition between parasitoid larvae within a host is contest (solitary parasitoids) or scramble competiti on (gregarious parasitoids). For gregarious parasitoids, a decreasing clutch size with increasing competition between females is predicted w hile for solitary parasitoids an increase is predicted. These predicti ons mere tested using the gregarious parasitoid Aphaereta minuta (M. E . Visser, 1996, Behav. Ecol. 7, 109-114) and the solitary parasitoid C omperiella bifasciata (J. A. Rosenheim and D. Hongkham, 1996, Anim. Be hav. 51, 841-852). Parasitoids were either kept alone or in groups bef ore the experiments, in which they were introduced singly into a patch containing unparasitized hosts. In the experiment with A. minuta, fem ales kept together before the experiment laid smaller clutches than fe males kept alone. In C. bifasciata, the clutch size laid by females ke pt together was larger than that of females kept alone. Thus, both pre dictions were supported. (C) 1998 Academic Press.