Factors affecting the rate of attack by Cotesia rubecula (Hymenoptera: Braconidae)

Abstract. 1. The relationship between responses of the insect parasitoid Cotesia rubecula (Marshall) to kairomones produced by the feeding activities of its host, Pieris rapae (L.), and patterns of parasitism were investigated under field conditions.
2. Parasitoid adults aggregated in patches with the highest densities of host larvae but there was no commensurate increase in the rate of attack in these patches.
3. The rate of attack was not limited by the availability of eggs.
4. The rate of parasitoid attack was highest where feeding damage by the host was highest, irrespective of current host density.
5. The rate of parasitoid attack was further influenced by host age distribution. Late instar larvae were less susceptible to parasitism than were early instar larvae. The rate of attack on early instar larvae occupying the same plants as late instar larvae was reduced. This reduction in rate of attack was due to limitations on parasitoid search time imposed by the increased feeding damage associated with large host larvae and by the increased time the parasitoid required to recover from an attack on these large host larvae.