Individual and combined effects of organophosphate and carbamate pesticides on the cricket frog Fejervarya limnocharis.

Many amphibians use water bodies associated with agro-ecosystem for breeding and thus are exposed to multiple chemicals. Fejervarya limnocharis is a common frog occurring in rice paddy fields. The timings of pesticide application generally coincide with the tenure of the occurrence of tadpoles in shallow waters of paddy fields. Malathion and carbaryl are frequently used in rice paddy fields to control leafhoppers and rice bugs, respectively. Therefore, effects of mixtures of malathion and carbaryl insecticides on the survival of tadpoles and emergence of froglets of Fejervarya limnocharis were studied in the laboratory using combinations of three concentrations of carbaryl (0, 25, 50 µg l-1) with four concentrations of malathion (0, 100, 250, 500 µg l-1). Both malathion and carbaryl were found to be toxic to tadpoles. A reduction in tadpole survival and froglet emergence was recorded with increasing concentrations of carbaryl and malathion. We found significant interaction between carbaryl and malathion on tadpole survival and froglet emergence. Tadpoles exposed to combination of pesticides showed early emergence as froglets compared to control. The extent of toxicity and pesticide interactions are varied when mixed in different concentrations. The reduction in survival, froglet emergence and delay in emergence of metamorphs can occur in rice paddy field as both pesticides are used simultaneously. Therefore, combinations of pesticides may have significant negative effects on the frog population of agro-ecosystems, which requires further confirmation through appropriate field experiments.