Olfactory host location and learning in the granary weevil parasitoidLariophagus distinguendus (Hymenoptera: Pteromalidae)

The sources of volatiles that attract the parasitoid Lariophagus distinguendus(Först.) to its hosts, the larvae of the granary weevil Sitophilus granarius(L.) infesting grains of Triticum aestivumL., were investigated in bioassays. The influence of oviposition experience on the responsiveness of the parasitoids to the sources of volatiles was considered. The potential sources of attractants are the host larvae, their 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 feces were removed were slightly attractive to inexperienced, but very attractive to experienced females. Healthy and artificially damaged grains were attractive to experienced parasitoids only. Refering to the “variable response model,” we discuss the effect of experience on the response of the parasitoids to the several stimuli. Stimuli from different 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.