ANTIFEEDANT COMPARISONS OF GABA GLYCINERGIC ANTAGONISTS FOR DIABROTICITE LEAF BEETLES (COLEOPTERA, CHRYSOMELIDAE)/

The phagostimulatory sensitivity of diabroticite (Coleoptera, Chrysome lidae, Galerucinae) species to cucurbitacins is not correlated with Cu curbitaceae specialization, indicating that other factors, including t he absence of feeding deterrents, may influence host-plant affinities among these beetles. Quinoline, indole, and isoquinoline alkaloids and sesquiterpene lactones believed to antagonize gamma-aminobutyric acid /glycine Cl- ionophores mediating chemoreception were tested on squash blossom disks for antifeedant activity to four diabroticite species w ith different host plant specializations. Most alkaloids were antifeed ant below 30 nmol/disk. Antifeedant concentrations of sesquiterpene la ctones were higher than alkaloids for all species. Oligophagous Diabro tica virgifera virgifera was more sensitive to quinoline alkaloids tha n polyphagous D. undecimpuntata howardi. Diabrotica virgifera virgifer a was also more sensitive to the indole alkaloids strychnine, brucine, eburnamonine, and vincamine than D. u. howardi. The closely related D . barberi had sensitivities similar to those of D. v. virgifera but th e more distantly related Acalymma vittatum was less sensitive to the a ntifeedants than D. v. virgifera. The isoquinoline alkaloid hydrastine was uniformly antifeedant to all diabroticites. All the GABA/glycine neurotoxicants tested against diabroticites were feeding deterrents an d suggest that beetles share a common antifeedant mechanism.