Naphthyl acetate esterase in the green rice leafhopper, Nephotettix cincticeps UHLER, with special reference to the resistant colony of the organophosphorus insecticide

Optimum conditions for determination of esterase in the green rice leafhopper was determined by using β-naphthyl acetate as substrate, and the difference between esterase activity of susceptible and organophosphorus resistant leafhopper was examined. This method was very sensitive, and it was found that the optimum concentration of homogenate was from 5ml to 20ml of buffer per adult and the reaction time was from 5min. to 20min. In larva, the esterase activity increased with age, the adult generally showed higher activity than larva and female was higher than male. The malathion resistant leafhopper had significantly higher activity of esterase than the susceptible one. Increase in esterase activity was closely correlated with malathion resistance. The ID-50 values of malaoxon and paraoxon for the esterase of malathion resistant colony were approximately the same as those of the susceptible colony. In both the resistant and susceptible leafhopper, the esterase activity consisted of cholinesterase and Besterase. The ratio of each esterase activity to total esterase activity was not differed between the resistant and the susceptible leafhopper.