Patterns of Parasitism by Torymus capite on Hosts Distributed in Small Patches

Abstract

SUMMARY (1) Patterns of parasitism inflicted by Torymus capite (Huber)(Hymenoptera: Torymidae) on its gall-making host were examined under laboratory conditions. Galls contained one to five larvae; each gall was considered a 'patch' of hosts. (2) As the number of hosts in a gall increased, so did its probability of being attacked. When several hosts were in an attacked gall the parasitoid tended to leave some unparasitized. These patterns opposed one another so that there was no correlation between the number of hosts per gall and the probability of a host being parasitized. (3) Gall size increased with the number of hosts within, but the larger, multi-host galls were no more 'discoverable' by T. capite than those with a single host. Attack frequency was lower in galls with few hosts because gall morphology made them less accessible to the parasitoid. As their number per gall increased, hosts lay closer to the gall's margin, and within the reach of T. capite's ovipositor. The probability of a discovery leading to a successful attack increased with host number.