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Abstract-The toxicity of endosulfan insecticide to wood frog (Rana sylvatica) embryos and tadpoles of wood frogs, American toads (Bufo americanus), and green frogs (R. clamitans) was examined in the laboratory. Following exposures to 0.03 to 0.4 mg/L endosulfan for 96 h, sublethal effects and postexposure mortality were assessed. In another experiment, premetamorphic American toad tadpoles (with developing hindlimbs but unerupted front legs) were exposed to 0.3 mg/L endosulfan for 96 h. The exposed wood frog embryos hatched successfully and were morphologically indistinguishable from the unexposed animals at the end of the 10-d postexposure period. However, extensive paralysis of exposed tadpoles of all three species occurred; all but one of the exposures resulted in 100% of the tadpoles experiencing paralysis at some point during the exposure or recovery period. Postexposure mortality of tadpoles was high and occurred at the lowest exposure concentrations (0.041-0.053 mg/L) for each species exposed as 2-week-old tadpoles. Newly hatched American toad tadpoles were more tolerant than tadpoles of the other two species, but no clear species differences in sensitivity of 2-week-old tadpoles was apparent. American toad premetamorphs exposed to endosulfan did not recover from the effects of the exposure. Our results indicate that the aquatic stages of anuran amphibians may be sensitive to levels of the pesticide endosulfan that could reach their habitat by means of direct applications or drift from aerial spraying.

The insecticide fenitrothion is sprayed twice, 5 to 10 d apart, to control spruce budworm. To assess the effects of pulsed exposure of fenitrothion to different species of amphibians, we exposed 1‐ and 8‐d‐old tadpoles of wood frogs, leopard frogs, green frogs, bullfrogs, and American toads, as well as larvae of the spotted salamander, to 2 to 9 ppm of the insecticide for 24 h. Our results indicate that within each ranid species, day‐1 and day‐8 tadpoles are equally sensitive, and tadpoles exposed twice, on day 1 and day 8, are no more sensitive to the second exposure than to the first. Bullfrog and green frog tadpoles are more sensitive to exposures than are wood frog and leopard frog tadpoles, exhibiting paralysis at lower concentrations, and they are affected by exposure to the carrier compounds as well as the insecticide. The greater sensitivity of the green frog and bullfrog tadpoles correlates with their smaller size and earlier developmental stage at hatching. American toad tadpoles are more tolerant of pu sed exposure to fenitrothion than are any of the ranids, whereas the spotted salamander larvae are as sensitive as are the bullfrog and green frog tadpoles.

Abstract-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.

Temperate zone amphibians are exposed to the maximum change in UV-B radiation influx during early stages of their development. Embryos and tadpoles of six anurans, Bufo americanus, Rana sylvatica, Rana pipiens, Rana clamitans, Rana catesbeiana, and Hyla versicolor, and embryos and larvae of two salamanders, Ambystoma maculatum (the yellow-spotted salamander) and Ambystoma laterale (the blue-spotted salamander), were exposed to different UV-B radiation regimes in containers (12 cm in diameter and 4.5 cm deep) with Nitex screening (1 mm) on the sides to permit natural exchange with pond water. The containers were secured to a floating structure in a small natural pond in south-central Ontario, where most of the species tested lived and successfully recruited offspring. Three exposure conditions were evaluated: (i) natural incident light, (ii) incident light with the UV-B radiation filtered out, and (iii) incident light with the UV-B radiation enhanced by UV-B lamps. Embryos of all species hatched successfully under enhanced and incident UV-B radiation conditions. However, salamander larvae and anuran tadpoles were sensitive to enhanced UV-B radiation conditions and a differential sensitivity was observed based on developmental stage. When 2 weeks old, anuran tadpoles showed greater sensitivity than when newly hatched. Incident levels of UV-B radiation had no significant effect on tadpoles or larvae. Because of the tolerance of the embryos and the very rapid attenuation of UV-B radiation in the water of small ponds (high in dissolved organic carbon (DOC)), little direct damage is likely to occur during the aquatic stages of these amphibians.