Toxicity and neurophysiological effects of fipronil and fipronil sulfone on the western corn rootworm (Coleoptera: Chrysomelidae).

摘要

The toxicity and neurophysiological effects of fipronil and its oxidative sulfone metabolite (5-amino-1-(2,6-dichloro-4-triflouromethylphenyl)-3-cyano-4-trifluoromethylsulfonylpyrazole) were investigated by using an insecticide-susceptible western corn rootworm (Diabrotica virgifera virgifera) population. In topical bioassays using adults, fipronil was toxic at very low concentrations (LD50 = 0.07 ng/mg; LD90 = 0.33 ng/mg). At the LD90, pre-treatment with the cytochrome P-450 monooxygenase inhibitor piperonyl butoxide led to mild antagonism of fipronil toxicity (LD90 = 0.42 ng/mg), while the sulfone analog had greater toxicity (LD90 = 0.22 ng/mg). In neurophysiological studies of spontaneous electrical activity, adult and larval rootworms were equally affected by fipronil and the sulfone analog at 10μM (in the presence of 5 mM GABA) in comparison to GABA-treated baselines. Using larval rootworms, insensitivity of the GABA receptor to binding by picrotoxinin or dieldrin (10μM) was not apparent in the presence of 5 mM GABA. Further neurophysiological investigation using a range of concentrations (0.625-20.0μM) on larval rootworms indicated concentration-dependent effects on bursting activity for both fipronil and the sulfone analog. However, subtle differences were observed between these two compounds. Results indicate that both fipronil and its oxidative sulfone metabolite have similar toxicological and neurological effects on rootworms.