The susceptibility of Spodoptera frugiperda (1. E. Smith) to methomyl. diazinon, and permethrin in relation to larval development was investigated. Increased LD,,,s of these insecticides were associated with increasing larval instars. Sixth instars were 135-, 154-, and 236-fold more tolerant of methomyl, diazinon, and permethrin, respectively, than were 3rd instars on a per-larva basis; the tolerances became 3. I -, 3.2-, and 5.6-fold, respectively, on a body weight basis. In all instances, a larger difference in tolerance was observed between 5th- and 6th-instars than between any other two successive instars. The fact that injection of methomyl into the 5th- and 6th-instars thereby bypassing the cuticle, did not alter the tendency suggests that the large increases in tolerance in the final instars were not related to cuticular penetration. Biochemical studies revealed that increased midgut aldrin epoxidase activity was associated with increased larval instars on a protein basis. A similar pattern was also observed for the midgut glutathione S-transferase activity, whereas the midgut esterase activity appeared to be higher in younger instars. Piperonyl butoxide, the well-known inhibitor of microsomal oxidases, enhanced the toxicity of these insecticides in this insect. Changes in microsomal oxidase activity correlate well with the toxicity of these insecticides to fall armyworm larvae.
Document Type: Research Article
Publication date: April 1, 1983
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Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.