Toxicity of insecticides to Toxorhynchites splendens and three vector mosquitos and their sublethal effect on biocontrol potential of the predator.

Toxicity of six larvicides ie fenthion, temephos, malathion, deltamethrin, alphamethrin (Fendona), OMS 3031 and five adulticides ie malathion, fenitrothion, propoxur, deltamethrin, permethrin to Aedes aegypti, Culex quiquefasciatus, Anopheles stephensi and the predator, Toxorhynchites splendens was studied for evaluating safety margin. Concentrations of alphamethrin that killed 50% larvae of T. splendens were 53 and 12 times more than that which killed Cx. quinquefasciatus and Ae. aegypti. In case of deltamethrin, concentrations required to kill 50% larvae of T. splendens were 14 and 5 times more than that required against other two species. Other larvicides tested were equally toxic to both T. splendens and vector mosquitos. There was no significant difference in the toxicity of larvicides to T. splendens and An. stephensi. Deltamethrin was 25-132 times less toxic to adults of T. splendens in comparison to vector mosquitos. For other adulticides the range was 1-10. Immature developmental time of T. splendens was not affected by any of the insecticides tested. However, predation rate was lowered when larvae of Ae. aegypti previously exposed to fenthion and temephos were offered. Whereas, alphamethrin and OMS 3031 did not affect the feeding rate of the predator. There was a significant reduction in the pupal weight and pupation as a result of the predator feeding on the insecticide treated prey. There was a significant negative relationship between rate of pupation and dosage. The present study indicates that synthetic pyrethroids owing to their higher safety margin can be used in an integrated vector management program.