Recognition of Native Host Volatiles by Laboratory Reared Trichogramma chilonis Ishii

Abstract

It is well known that many trichogrammatids use volatiles from hosts or host plants during host location. When such parasitoids are reared continuously on factitious hosts in the laboratory it is believed that they may lose their ability to recognize the volatiles from their native hosts or change their host preference. Hence, this study was carried out to investigate whether Trichogramma chilonis Ishii reared on Corcyra cephalonica (Stainton) was able to recognize the volatiles of two of its native hosts in sugarcane, viz., Chilo infuscatellus Snellen and Chilo sacchariphagus indicus (Kapur). The per cent parasitoids responding to the olfactory cues, namely, the hexane-washings of eggs, scales, adult body and pheromone lures of target hosts, was assessed in nochoice and dual-choice bioassays in a "Y"-tube olfactometer. For comparison, C. cephalonica washings were used. The results indicated attraction of T. chilonis to volatiles from washings of all host sources at different levels with highest per cent parasitoids attracted to C. sacchariphagus indicus egg washings. Overlapping significant levels of attraction was found with the scale and adult body washings of fresh mated moths of all three species in no-choice tests, while C. sacchariphagus indicus was the most preferred in dual-choice tests. Volatiles from male moths were more attractive to T. chilonis than those from female moths. The parasitoids failed to respond to the body washings of >72h old moths of all the three species. Attraction of T. chilonis to the synthetic sex pheromone lures of two native hosts was observed but the parasitoid did not discriminate between them. These findings suggest that though reared on a factitious host, T. chilonis is able to recognize and respond to the native host cues and there is no change in the innate preference of the parasitoid which may have to be further confirmed with parasitism studies.