Mechanisms of Resistance to Organophosphorus and Carbamate Insecticides in Oriental Fruit Moth Populations (Grapholita Molesta Busck)

Abstract

Mechanisms of resistance to organophosphorus and carbamate insecticides were investigated in larvae and adults of the oriental fruit moth,Grapholita molesta(Busck). Comparative studies with an N-methyl carbamate (carbofuran) tested with or without synergists indicated that more than one factor contributed to insecticide resistance in the oriental fruit moth. Increases in esterase activity in both larvae and adults of resistant strains toward α-naphthyl acetate (5.5-fold for third instar larvae, 3.9-fold for adults), β-naphthyl acetate (4.6-fold for third instar larvae, 3.8-fold for adults), α-naphthyl butyrate (4.2-fold for third instar larvae, 5.5-fold for adults), and β-naphthyl butyrate (2.6-fold for third instar larvae, 2.8-fold for adults) model substrates and differences between strains in esterase patterns resolved using isoelectric focusing indicated that esterases were major factors in the resistance of the oriental fruit moth to insecticides. Differences between resistant and susceptible strains in inhibition of acetylcholinesterases by guthoxon (6-fold for third instar larvae, 10.5-fold for adults), carbofuran (33-fold for third instar larvae, 53.5-fold for adults), carbaryl (43.8-fold for third instar larvae, 1757.4-fold for adults), and methomyl (3.3-fold for third instar larvae, 8-fold for adults) indicated that target site insensitivity was another major resistance factor. Measurements of penetration of radiolabeled carbofuran in adults suggested that a decrease in insecticide uptake may supplement resistance provided by other mechanisms. Measurements of glutathione transferase, mixed-function oxidase, and aliesterase activities failed to demonstrate that these factors were involved in resistance. Because resistance is expressed in both larvae and adults, monitoring for resistance is appropriate with these insecticides in either life stage.