Physiological and behavioral dose-responses of the lesser chestnut weevil, Curculio sayi, to host plant volatile organic compounds
The small chestnut weevil, Curculio sayi (Gyllenhal), is a significant chestnut pest that has grown in importance with the resurgence of the American chestnut industry. Small chestnut weevils lay their eggs in chestnuts where the larvae feed on the developing nut tissue. Afterwards, the larva emerges from the nut and burrows into the soil it remains there for a 1-2 year period. Following this long diapause, adult weevils emerge in the spring during catkin (flower) development, and then again in the late-summer/early-fall as the burs are maturing. Previous research identified a suite of host plant volatile organic compounds (VOCs) attractive to small chestnut weevils. Eight of the previously identified compounds were selected for further testing using electroantennagram (EAG) and Y-tube bioassays. Adult male and female weevils from both the spring and fall emergence periods were tested for each of the eight compounds at four different doses 0.1, 0.01, 0.001, and 0.0001 mg. The physiological dose response data obtained from the EAG assay showed both an increase response strength and significance as dose increased. The behavioral results from the Y-tube bioassay generally followed a similar pattern but less consistently with several of the lower doses showing skewed behavioral responses. Accounting for sex and season, four of the eight compounds including trans-2-hexenol, trans-2-hexenal, 2-heptanone, and ethyl butyrate were selected at the 0.1 mg dose for further experimentation focused on combining compounds.