Insecticide susceptibility in Coptotermes formosanus and Reticulitermes virginicus (Isoptera : Rhinotermitidae)

Lethal time to mortality responses were established for eight insecticides against workers and soldiers of the Formosan subterranean termite, Captoter mes formosanus Shiraki, and workers of Reticulitermes virginicus (Banks). T here were significant differences in the tolerance ratios between workers o f C. formosanus colonies to all toxicants tested except fipronil. One colon y was 16 times more tolerant than another to deltamethrin. C. formosanus so ldiers had significant differences in tolerance ratios among colonies expos ed to all toxicants except chlorpyrifos. Methoxychlor, permethrin, deltamet hrin, and fipronil did not kill soldiers from two, one, one, and three colo nies, respectively, within 8 h. Seventy-five percent of R. virginicus colon ies were significantly less susceptible than the most susceptible colony to chlordane, methoxychlor, chlorpyrifos, cypermethrin, and Fipronil, with 50 % of the colonies less susceptible to permethrin and bendiocarb. In 50% of C. formosanus colonies the worker lethal time curves displayed substantial flattening in response to permethrin, and deltamethrin. Lethal time curves for C.formosanus soldiers exposed to chlordane, chlorpyrifos, permethrin, c ypermethrin, deltarnethrin, and bendiocarb showed substantial flattening, R . virginicus workers demonstrated substantial curve flattening when exposed to chlordane, methoxychlor, chlorpyrifos, deltamethrin, and fipronil. Thes e findings indicate substantial intercolony and intra-colony differences in susceptibility to insecticides.