Residual Toxicity of Certain Newer Pesticides on Eupelmus tachardiae: A Parasitoid of Lac Insect Kerria lacca (Kerr)

Abstract

The work addresses the issue of large scale lac crop mortality caused by parasitoids associated with lac insect, Kerria lacca (Kerr) in some of the lac growing tracts of the country. Laboratory evaluation of four selective insecticides viz., fipronil, indoxacarb, spinosad and ethofenprox was carried out at different concentrations against adults of a primary parasitoid of lac insect, Eupelmus tachardiae (Howard) by exposing the test insects on residual film of insecticides. Insecticides identified and their concentrations selected on the basis of their safety evaluation trials towards lac insect, K. lacca (Kerr). All these insecticides have been recommended and are being used on lac culture for the effective management of insect predators (Lepidopteran and Neuropteran) attacking lac insect. The recommended concentrations for effective management of lac insect predators are fipronil (0.007 %), indoxacarb (0.007 %), spinosad (0.005 %) and ethofenprox (0.02 %). Insecticide fipronil (varied from 0.0012 to 0.01 %), indoxacarb (varied from 0.0017 to 0.02 %) and ethofenprox (varied from 0.01 to 0.04 %) were evaluated at five different concentrations whereas spinosad was evaluated at eight concentrations (varied from 0.00015 to 0.01 %) against E. tachardiae. On the basis of relative residual toxicity, fipronil was found to be most effective treatment followed by spinosad and indoxacarb. Ethofenprox was found to be relatively least effective treatment against the test insect. Fipronil, indoxacarb and spinosad causes cent % mortality of male and female E. tachardiae adults within 24 h of exposure on residual film of insecticides whereas some adults survival was observed with the treatment of ethofenprox during the same exposure period. Cent % mortality of male and female test insect was recorded with the treatment of fipronil (0.007 %) within 1.5 h exposure whereas spinosad (0.005 %) was resulted to 88.5 and 82.4 % male and female mortality of test insect, respectively under same exposure period (1.5 h). However, exposure of test insect on residual film of indoxacarb (0.007 %) and ethofenprox (0.02 %) exhibited no mortality of test insect within 1.5 h exposure. Indoxacarb (0.007 %) caused 65.5 and 53.8 % male and female mortality, respectively whereas ethofenprox (0.02 %) caused mortality of male and female insect to the tune of 12.5 and 15.4 %, respectively within 6 h of exposure. The relative toxicity of insecticides based on time period of knockdown after exposure to residual film of insecticides may be depicted as fipronil > spinosad > indoxacarb > ethofenprox.