Yu_1991_Pestic.Biochem.Physiol_39_84

A strain of the fall armyworm, Spodoptera frugiperda (J. E. Smith), collected from corn in North Florida showed resistance to commonly used insecticides. Resistance to pyrethroids (permethrin, cypermethrin, cyhalothrin, fenvalerate, tralomethrin, bifenthrin, tetramethrin, and fluvalinate) ranged from 2- to 216-fold; the highest resistance level observed was to fluvalinate. Resistance to organophosphorus insecticides (chlorpyrifos, methyl parathion, diazinon, sulprofos, dichlorvos, and malathion) ranged from 12- to 271-fold; the highest resistance level observed was to methyl parathion. Resistance to carbamates (methomyl, carbaryl, and thiodicarb) ranged from 14- to >192-fold with the highest resistance level being observed with carbaryl. Detoxication enzyme assays revealed that activities of microsomal oxidases (aldrin epoxidase, heptachlor epoxidase, biphenyl hydroxylase, p-nitroanisole O-demethylase, and phorate sulfoxidase) and hydrolases (helicin beta-glucosidase and acetylcholinesterase) were 1.4- to 6.6-fold higher in the field strain than in the susceptible strain. Levels of cytochrome P450 and cytochrome b5 were 1.7- and 1.3-fold higher, respectively, in the field strain than in the susceptible strain. In addition, the bimolecular rate constants for inhibition of acetylcholinesterase by dichlorvos and carbaryl were 2.8- and 3.5-fold higher, respectively, in the susceptible strain than in the field strain. There was no difference in the rate of cuticular penetration of carbaryl in both strains. The results indicated that the broad spectrum of insecticide resistance observed in the field strain was due to multiple resistance mechanisms, including increased detoxication of these insecticides by microsomal oxidases and target site insensitivity such as insensitive acetylcholinesterase.