The cotton bollworm endoparasitoid Campoletis chlorideae is attracted by cis-jasmone or cis-3-hexenyl acetate but not by their mixtures

Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) is an important larval endoparasitoid of the cotton bollworm Helicoverpa armigera (Hubner). A better understanding of herbivore-induced plant volatiles (HIPVs) employed by C. chlorideae to locate hosts will contribute towards the biological control of this notorious crop pest. In this study, we first investigated the electrophysiological and behavioral responses of C. chlorideae to 19 volatile compounds emitted by herbivore-infested plants. Eleven odorants induced EAG responses of C. chlorideae, while only two compounds, cis-jasmone and cis-3-hexenyl acetate, were attractive to the parasitoid in Y-tube olfactometer assays. Next, we used two- and four-choice tests in cage settings to investigate the parasitism rate of H. armigera larvae by C. chlorideae on tobacco plants treated with different doses of cis-jasmone, cis-3-hexenyl acetate, and their mixtures. Results showed that the parasitism rate of H. armigera was significantly higher on the plants treated with cis-jasmone or cis-3-hexenyl acetate, and their optimal dose for both compounds was 1 mg. However, the mixtures of cis-jasmone and cis-3-hexenyl acetate did not increase H. armigera parasitism rate by C. chlorideae when compared with control groups. Our results indicate that the single compounds cis-jasmone and cis-3-hexenyl acetate, at certain doses, enhance parasitic efficiency of C. chlorideae, but their mixtures negate this effect. These results will help us in the exploitation of C. chlorideae as biological control agent to reduce the populations of H. armigera.