POLYACRYLAMIDE-GEL ELECTROPHORETIC ASSESSMENTS OF ESTERASES IN COTTONAPHID (HOMOPTERA, APHIDIDAE) RESISTANCE TO DICHLORVOS

The role of esterases in dichlorvos resistance of die cotton aphid, Ap his gossypii Glover was studied by vertical slab polyacrylamide gel el ectrophoresis by using a susceptible (E-S) and dichlorvos-selected res istant (E-D-R) strain. Results suggested that both resistant and susce ptible strains possessed bands E-2, E-11, and E-12, with the latter 2 bands of the resistant strain comigrating slightly faster compared wit h the susceptible strain. On addition, the resistant strain had additi onal bands (i.e., E-1, and E-3 to E-10), which probably reflected from changes in conformation. Although bands of both strains exhibited equ al affinity (with the shorter naphthyl acetates and indoxyl acetate), none had affinity with naphthyl laurate and myristate. The most elevat ed in the resistant strain were E-7, E-9, and E-10, which were classif ied as carboxylesterases. Bands E-11 and E-12 in both strains were cla ssified as eserine sulfate sensitive carboxylesterases. Excessive prod uction 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.