Polyacrylamide gel electrophoretic assessments of esterases in cotton aphid (Homoptera: Aphididae) resistance to dichlorvos

The role of esterases in dichlorvos resistance of the cotton aphid, Aphis gossypii Glover was studied by vertical slab polyacrylamide gel electrophoresis by using a susceptible (E-S) and dichlorvos-selected resistant (E-D-B) strain. Results suggested that both resistant and susceptible strains possessed bands E-2, E-11, and E-12, with the latter 2 bands of the resistant strain conmigrating slightly faster compared with the susceptible strain. On addition, the resistant strain had additional bands (i.e., E-1, and E- to E-10), which probably reflected from changes in conformation. Although bands of both strains exhibited equal affinity (with the shorter naphthyl acetates indoxyl acetate), none had affinity with naphthyl laurate and myristate. The most elevated in the resistant strain were E-7, E-9, and E-10, which were classified as carboxylesterases. Bands E-11 and E-12 in both strains were classified as eserine sulfate sensitive carboxylesterases. Excessive production of comigrating bands of carboxylesterases in both quantitative and qualitative forms, coupled with modification of these enzymes, may account for dichlorvos resistance in this aphid.