Resistance Mechanisms in Two Color Forms of the Tobacco Aphid (Homoptera: Aphididae)

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Abstract
Cultures of the tobacco aphid, Myzus nicotianae Blackman, were collected from tobacco throughout major tobacco-growing regions of North Carolina and maintained in culture in the laboratory. Nine cultures of tobacco aphids were established. Four of these cultures were green in color; five were red. Slide-dip tests were performed with various insecticides and a known synergist. In tests with malathion, monocrotophos, acephate, and the esterase inhibitor S, S, S-tributyl phosphorotrithioate (DEF), resistance of aphids from the five red cultures and one green culture (from Duplin County) increased three to four times compared with the remaining three green cultures. In tests with endosulfan and methamidophos, a breakdown product of acephate, all nine cultures responded equally to treatment. Total carboxylesterase activities of aphids from all nine cultures were measured in a spectrophotometric assay. Aphids from the five red cultures and the green culture from Duplin County demonstrated ≈2.5 times the carboxylesterase activity as aphids from the remaining three green cultures. In all cultures, synergism of malathion, acephate, and methamidophos by DEF was apparent.