No abstract

AceIn, a gene controlling acetylcholinesterase inhibition and dominantly-inherited resistance to methyl parathion, was monitored in Heliothis virescens across the southeastern USA. The resistant allele, AceIn-R, was detected in 13 collections from 1989 to 1993 with an average frequency of 14.1±3.9%. This resistance mechanism was found in pheromone-trapped moths from Texas, Mississippi, Georgia and South Carolina. Genotype frequencies agreed with Hardy-Weinberg predictions. This resistance allele occurs at a low frequency in apparent equilibrium despite the widespread substitution of pyrethroid insecticides for methyl parathion. Laboratory colonies collected from South Carolina in previous years when there was more extensive use of methyl parathion exhibited higher frequencies. Results are discussed regarding the evolution of resistance and in relation to resistance management strategies.Insecticide resistance evolves in populations under selection by insecticides as documented for hundreds of species (7,2); however, the role of specific genes in the development of resistance in the field has been studied in only a few cases (3). Examples of monitoring for specific genes using enzyme or nucleic acid analyses in microtiter plate readers has demonstrated the correlation to resistance of carboxylester hydrolase activity in aphids (4-6) and mosquitoes (7-9) and the correlation to resistance of insensitive acetylcholinesterase in planthoppers (10,11), house flies (12), whiteflies (13) and mosquitoes (14,15).In pests with several potential mechanisms for resistance, it will be most important to monitor susceptibility as well as several resistance genes in order to understand the population genetics of resistance development. The tobacco budworm, Heliothis virescens (L.) (Lepidoptera: Noctuidae), possesses several mechanisms giving resistance to methyl parathion (16-18); therefore, in order to diagnose resistance in a population of this pest, it will be necessary to assay individuals for several potential resistance genes. One step in this direction is to