Laboratory study of insecticidal impact on the sensitivity of different stages in the assassin bug Rhynocoris longifrons (Stalº): (Hemiptera: Reduviidae)

Abstract

Stage specific sensitivity was studied for five commonly used insecticides in the agroecosystem namely quinalphos, chlorpyrifos, dimethoate (Organophosphorous insecticides) and deltamethrin and bifenthrin (Pyrethroid insecticides) on the assassin bug Rhynocoris longifrons (Stal). All the three organophosphorous insecticides caused 100% mortality in all the durations of treatment (24, 48, 72 and 96hrs) in the first, second and third instar nymphs of R. longifrons. In the fourth, fifth instar nymphs and adult insects only quinalphos and chlorpyrifos caused 100% mortality in R. longifrons. The pyrethroid insecticides did not cause 100% mortality in all the durations in all the nymphal instars and adults. The results will enable strategies for compiling the biological control and chemical control. The laboratory studies revealed that organophosphate was considered the most toxic for all the nymphal instars and adults of R. longifrons whereas synthetic pyrethroids were considered relatively safer insecticides for all the other nymphal instars and adults of R. longifrons. This study demonstrates how the indiscriminate use of insecticides as a pest management strategy can directly disrupt the benefits of natural enemies.