Behavioral adaptations in host finding by Trichogramma evanescens: the influence of oviposition experience on response to host contact kairomones

The influence of oviposition experience on the response of the egg parasitoid Trichogramma evanescens Westwood (Hymenoptera Trichogrammatidae) towards the contact kairomones of two different host species, Mamestra brassicae (L.) and Pieris brassicae L., is described. The response of T. evanescens was influenced by the number of eggs it had laid, but time since oviposition did not result in a significant change in behaviour. Parasitoids readily accepted an egg of a second species and the time spent searching in a particular kairomone area would appear to depend on the reproductive state and expected survival of a parasitoid, rather than the development of any host preference. Trichogramma seems to select patches on the basis of reward probability rather than maximising reward size. Such behaviour would assist parasitoids to respond to fluctuations in host availability.