EFFECTS OF THE SYNTHETIC PYRETHROID INSECTICIDE, ESFENVALERATE, ON LARVAL LEOPARD FROGS (RANA SPP)

Leopard frog (Rana spp.) tadpoles exposed to esfenvalerate in the labo ratory experienced a decrease in activity at concentrations as low as 1.3 mu g/L and exhibited a convulsive, twitching response at concentra tions of 3.6 mu g/L. The 96-h median lethal concentration was 7.29 mu g/L. Temperature influenced amphibian mortality; the mortality concent ration-response slope at 22 degrees C was significantly greater than a t 18 degrees C. Tadpoles exposed in a pond showed the same responses ( inactivity, convulsive actions, and death) at similar concentrations a s laboratory test organisms. Surviving tadpoles from laboratory tests resumed normal behavior 1 week after being placed into clean water, bu t most of those tadpoles that exhibited convulsive behavior during ini tial exposure eventually died. Tadpoles surviving pond exposures showe d no later mortality, but rather exhibited a negative density-growth r elation. Measured pyrethroid concentrations in ponds and streams adjac ent to sprayed fields do not exceed levels associated with convulsive twitching or mortality in larval amphibians; however, they do exceed c oncentrations associated with inactivity and fish and invertebrate mor tality, which may indirectly affect larval amphibians.