Role of metabolic enzymes in resistance to chlorpyrifos-methyl in the cowpea aphid, Aphis craccivora (Koch)

The cowpea aphid, Aphis craccivora management relies mainly on chemical control. As a result extensive and repeated treatment of insecticides has led to the development of aphid resistance to commonly used insecticides. To investigate chlorpyrifos-methyl resistance in A. craccivora, a field strain was selected for 24-generations to achieve a resistance factor of 82.3 fold compared with a susceptible strain. In the resistant strain, malathion and lambda-cyhalothrin exhibited obvious cross-resistance; while fenvalerate and dinotefuran showed moderate cross-resistance. In contrast, slight or no cross-resistance was obtained with the other tested insecticides. To investigate metabolic resistance mechanisms, integration of biochemical and synergism assays was conducted. Results showed the key role of esterase (EST) and mixed function oxidases (MFO); however, glutathione-s-transferase (GST) contributed less to resistance. Cross-resistance studies showed the need for rotation with non-cross resistant insecticides as a resistance management tactic.