ANTIFEEDANT EFFECTS OF SOME NOVEL TERPENOIDS ON CHRYSOMELIDAE BEETLES- COMPARISONS WITH ALKALOIDS ON AN ALKALOID-ADAPTED AND NONADAPTED SPECIES

Structure-dose-feeding deterrency relationships were compared between the Colorado potato beetle, Leptinotarsa decemlineata (Say), and the w estern corn rootworm, Diabrotica virgifera virgifera LeConte, using 15 alkaloids, terpenoids, and phenolic derivatives. The former species, a specialist herbivore on selected alkaloid-rich Solanaceae species, w as on average 100-times less sensitive to the antifeedant effects of a lkaloids, but more similarly sensitive to the terpenoids and phenolics than the fatter species, a generalist flower herbivore predominantly on Graminae, Cucurbitaceae, and Compositae species. Antifeedant ED50 v alues for the potato beetle and corn rootworm, each from closely relat ed subfamilies of Chrysomelidae, ranged over four orders of dose magni tude among the 15 compounds with major species differences in stereose nsitivity to beta-hydrastines and analog sensitivity with the silphine nes. Extremes in sensitivity ranged from silphinene, a rare tricyclic sesquiterpene that is 53 times more active on the potato beetle to aco nitine, which is 430 times more antifeedant to the corn rootworm. Amon g silphinene and its two hydrolysis derivatives, there was not a stron g correlation between antifeedant potency and injected toxicity for th e two beetle species, but there was correlation between behavioral act ivity and galeal taste cell electrophysiological threshold and frequen cy responses. That all of the established GABA- and glycinergic compou nds tested were antifeedant for both species suggests a shared molecul ar mechanism for antifeedant taste chemoreception in these divergent C hrysomelidae species. Moreover, the wide differences in antifeedant se nsitivities among these and other chrysomelids to a suite of ligand-ga ted ion channel antagonists implicate a common protein neuroreceptor t ype with extraordinary heterogeneity in beetle taste.