Antifeedant Comparisons of GABA/Glycinergic Antagonists for Diabroticite Leaf Beetles (Coleoptera: Chrysomelidae)

The phagostimulatory sensitivity of diabroticite (Coleoptera, Chrysomelidae, Galerucinae) species to cucurbitacins is not correlated with Cucurbitaceae specialization, indicating that other factors, including the absence of feeding deterrents, may influence host–plant affinities among these beetles. Quinoline, indole, and isoquinoline alkaloids and sesquiterpene lactones believed to antagonize γ-aminobutyric acid/glycine Cl− ionophores mediating chemoreception were tested on squash blossom disks for antifeedant activity to four diabroticite species with different host plant specializations. Most alkaloids were antifeedant below 30 nmol/disk. Antifeedant concentrations of sesquiterpene lactones were higher than alkaloids for all species. Oligophagous Diabrotica virgifera virgifera was more sensitive to quinoline alkaloids than polyphagous D. undecimpuntata howardi. Diabrotica virgifera virgifera 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 the more distantly related Acalymma vittatum was less sensitive to the antifeedants than D. v. virgifera The isoquinoline alkaloid hydrastine was uniformly antifeedant to all diabroticites. All the GABA/glycine neurotoxicams tested against diabroticites were feeding deterrents and suggest that beetles share a common antifeedant mechanism.