Relationship of insecticide resistance to carboxylesterases in Aphis gossypii (Homoptera: Aphididae) from Midsouth cotton

Laboratory assays were done to quantify proportions of phenotypes in laboratory oratory colonies resistant to several classes of insecticides in the cotton aphid, Aphis gossypii Glover. Resistance to a carbamate (aldicarb), an organochlorine (endosulfan), an organophosphate (chlorpyrifos), and a pyrethroid (bifenthrin) was documented. Significant declines in numbers of individuals resistant to bifenthrin and endosulfan but not for chlorpyrifos occurred during a 5-mo interval after the first bioassays. Resistance ratios between clonal susceptible and resistant cotton aphid colonies for chlorpyrifos indicated a significant 4-fold difference in LC50 estimates for the two colonies. Spectrophotometric analyses indicated significantly higher carboxylesterase activity in resistant aphids compared with susceptible aphids. Results from isoelectric polyacrylamide focusing gel techniques also showed differences in carboxylesterases, both in differences in banding patterns and in expression of comigrating bands