DETECTION AND BIOCHEMICAL-CHARACTERIZATION OF INSECTICIDE RESISTANCE IN FALL ARMYWORM (LEPIDOPTERA, NOCTUIDAE)

Two field strains of the fall armyworm, Spodoptera frugiperda (J. E. Smith), collected from com in central and south Florida in 1990 showed resistance to commonly used insecticides as compared with a laboratory susceptible strain. Resistance to pyrethroids ranged from 3- to 264-fold; the highest resistance level observed was to fluvalinate. Resistance to organophosphates ranged from 11- to 517-fold; the highest resistance level observed was to methyl parathion. Resistance to carbamates ranged from 10- to 507-fold with the highest resistance level being observed with carbaryl. Detoxification enzyme assays revealed that activities of microsomal oxidases (epoxidases, hydroxylase, sulfoxidase, N-demethylase, and O-dealkylases), glutathione transfemses (DCNB and CDNB), hydrolases (general esterase, carboxylesterase, beta-glucosidase, and acetylcholinesterase), and reductase (cytochrome c reductase) were 1.2 to 11.0-fold higher in field strains than in the susceptible strain. The detoxification enzyme activities were generally more heterogeneous in populations of field strains than in that of the susceptible strain. Certain field strains were less inducible by allelochemicals than the susceptible strain with respect to microsomal oxidase and glutathione transferase. In addition, the bimolecular rate constants for inhibition of acetylcholinesterase by dichlorvos were 4.3- to 7.8-fold higher in the susceptible strain than in field strains. The broad spectra of insecticide resistance observed in field strains were due to multiple resistance mechanisms, including increased detoxification of these insecticides by microsomal oxidases, glutathione transferases, and esterases; and target site insensitivity (such as insensitive acetylcholinesterase).