Detoxifying Enzymes in Greenhouse and Laboratory Strain of Beet Armyworm (Lepidoptera: Noctuidae)

Abstract

J. Econ. Entomol. 88(4): 777-781 (1995) The intensive use of insecticides to control the beet armyworm, Spodoptera exigua, in greenhouse crops in The Netherlands may lead to tolerance. Differences in toxicity to commonly used insecticides are explored in a laboratory susceptible population obtained from France (L) and a population collected from greenhouses in The Netherlands (G), in which reduction in pesticide efficacy was observed. The greatest reduction in susceptibility for the G strain was noticed with deltamethrin (6- to 8-fold). We detected no difference in biological activity toward methomyl between the 2 pest populations. The G:L ratio at the LC 50 level for L 5 larvae was 2.2 and 3.1 for diflubenzuron and teflubenzuron, respectively. Rates of enzyme activity were significantly greater in the greenhouse population than in larvae from the laboratory-susceptible population for the substrates of glutathione S-transferases (1-chloro-2,4-dinitrobenzene [CDNB] [1.2-fold], 1,2-dichloro-4-nitrobenzene [DCNB] [1.4-fold]), microsomal oxidases (N-demethylase [1.4-fold], and O-demethylase [2-fold]), carboxylamidases (1.7-fold), and acetylcholinesterases (1.5-fold). We observed no significant differences between the rates of general ester hydrolysis for α- and β-naphthyl acetate. The G strain appears to have less sensitive acetylcholinesterases, because bimolecular order rate constants were 1.9-and 2.7-fold lower for methomyl and dichlorvos, respectively. In addition to target site insensitivity in the G population, the diversity of enhanced detoxifying enzymes may contribute to a reduced susceptibility to a wide range of insecticides.