OLFACTORY HOST LOCATION AND LEARNING IN THE GRANARY WEEVIL PARASITOIDLARIOPHAGUS-DISTINGUENDUS (HYMENOPTERA, PTEROMALIDAE)

The sources of volatiles that attract the parasitoid Lariophagus disti nguendus (Forst.) to its hosts, the larvae of the granary weevil Sitop hilus granarius (L.) infesting grains of Triticum aestivum L., were in vestigated in bioassays. The influence of oviposition experience on th e responsiveness of the parasitoids to the sources of volatiles was co nsidered. The potential sources of attractants are the host larvae, th eir feces, and the grain infested by the host. Weevil larvae were not attractive. Feces were attractive to females without and females with oviposition experience. Infested grains from which the larvae and fece s were removed were slightly attractive to inexperienced, but very att ractive to experienced females. Healthy and artificially damaged grain s were attractive to experienced parasitoids only. Refering to the ''v ariable response model,'' we discuss the effect of experience on the r esponse of the parasitoids to the several stimuli. Stimuli from differ ent trophic levels are used by the foraging parasitoids: feces of the host larvae is an important source of attractants, but also the grains , particularly after experience.