Genetics and Synergism of Resistance to Azinphosmethyl and Permethrin in the Colorado Potato Beetle (Coleoptera: Chrysomelidae)

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Abstract
A strain of Colorado potato beetle, Leptinotarsa decemlineata (Say), from Massachusetts was 435 times more resistant to azinphosmethyl than a susceptible strain from North Carolina. Reciprocal backcrosses suggested that resistance is due to a single incompletely dominant autosomal factor. Dominance may be influenced by the genome of the insect strain. Azinphosmethyl was synergized with an esterase inhibitor, S, S, S-tributyl phosphorotrithioate, in susceptible and resistant strains; moderate levels of synergism occurred with the glutathione-S-transferase inhibitor diethyl maleate and the monooxygenase inhibitor piperonly butoxide in only the resistant strains. Permethrin resistance was 55 times greater in the Massachusetts resistant strain compared with the susceptible strain. Reciprocal backcrosses suggested that permethrin resistance is due to a sex-linked, semirecessive factor that appears to confer cross-resistance to other pyrethroids, although not at the same levels as to permethrin. Permethrin was synergized by S, S, S-tributyl phosphorotrithioate and piperonyl butoxide in susceptible and resistant strains, but synergism was enhanced in the resistant strains. Diethyl maleate did not synergize permethrin in the susceptible strain but synergized the Massachusetts strain.