EFFECTS OF AGE, REPRODUCTIVE ACTIVITY, SEX, AND PRIOR EXPOSURE ON SENSITIVITY TO CUCURBITACINS IN SOUTHERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE)

Cucurbitacins, toxic to most organisms, are arrestants its and phagost imulants for diabroticite chrysomelid beetles. Little is known about v ariation in the response of diabroticites to cucurbitacins. To quantif y the effects of age, sex, reproductive status, and prior exposure to cucurbitacins on the sensitivity to cucurbitacin B of the southern cor n rootworm, Diabrotica undecimpunctata howardi Barber, beetles were se parated by sex and grouped for treatment with diets including or exclu ding cucurbitacins. Sensitivity to cucurbitacins was assayed over the first 43 d of adulthood by exposing beetles in groups of five for 24 h to filter paper strips spotted with serial methanol dilutions of cucu rbitacin B ranging from 800 to 0.1 ng/ml. The areas consumed by the be etles at each dilution were then measured, and dose-response curves fo r each treatment were drawn. Treatments were compared in terms of the area under the mean dose response curve (AUC). Sex, age, reproductive activity, and prior exposure to cucurbitacins all significantly affect ed beetle sensitivity, though prior exposure was the most consistent i n its effect. Exposure to cucurbitacins for as little as 6 d permanent ly reduced sensitivity, whereas beetles without prior exposure remaine d sensitive to our assay throughout the study. Reproductive activity d epressed sensitivity in males but increased sensitivity in females. Th ese results are discussed in terms of their relevance to semiochemical diabroticite baits and also to the proposed role of cucurbitacins in protecting these beetles from predators, parasites, or pathogens.