Abstract: Oligophagous Helicoverpa assulta (Guenée) and polyphagous H. armigera (Hübner) are two sibling species of Heliothis. In crops, H. assulta was rarely found in cotton or tomato fields, and there was almost no H. armigeraon hot pepper, only tobacco was the host plant which both of them preferred to and coexisted on. In order to further understand the effects of plant volatiles on insects' host orientation and selection behavior, the electroantennograms (EAGs) and wind tunnel response of virgin females, mated females, and males of the two species to 20 tobacco volatile compounds at a high concentration (0.1 mol/L), respectively, were recorded. The results showed that both species elicited the similar EAG responses to the tested tobacco volatile compounds, which mainly presented as green leaf volatiles> aliphatic and aromatic compounds> monoterpene, sesquiterpene and heterocyclic compounds.  There were no significant sexual or interspecific differences between the two species in EAG responses to most of the compounds, which suggested that the olfactory neural system of them might have the similar discrimination capability and sensibility, leading to the same “understanding" to the chemical information from their host plants. The behavioral response was essentially identical with the EAG response, i.e., there was consistency between olfactory stimulus and behavioral response of the two sibling species. Considered the obvious difference of their host range, it was inferred that tobacco volatiles was just to affect insect's host orientation, while the host selection behavior of the two species may mainly depended on the process to evaluate the physical and chemical properties of the tobacco plant after contacting or landing on the host plant.

Key words: Helicoverpa armigera, Helicoverpa assulta, electroantennogram (EAG), tobacco plant volatiles, wind tunnel, chemical communication, host orientation