Sensitivity of amphibian embryos and tadpoles to Mimic 240 LV insecticide following single or double exposures

Mimic 240 LV is a novel, narrow-spectrum insecticide containing the active ingredient tebufenozide. Tebufenozide mimics the action of the insect molting hormone ecdysone and shows specific activity toward larval Lepidoptera. In Canada, Mimic 240 LV has been proposed for use in forest pest control, whereas a different formulation has been registered for use in agriculture. We examined the effects of single and double pulses of Mimic 240 LV (tebufenozide) on the development, growth, and predator avoidance behavior of four frog species (wood frogs Rana sylvatica, leopard frogs R. pipiens, green frogs R. clamitans, and bullfrogs R. catesbeiana) exposed in the laboratory as embryos or tadpoles. Nominal doses ranged from 3.0 mg/L to 9.0 mg/L tebufenozide, and exposures were terminated at 96 h following single, or 192 h following double, exposures. More than 90% of the animals exposed as embryos hatched. Embryos exposed late in development and subsequently hatching into tebufenozide-contaminated water all hatched and responded normally. Tadpole growth was not delayed following exposure, and premetamorphic green frogs successfully completed metamorphosis following exposure to the highest concentration. The results suggest that Mimic 240 LV, when used at the suggested application rates, will not severely affect the aquatic stages of ranid amphibians.