Monitoring For Insecticides Resistance In The Green Apple Aphid (Homoptera: Aphididae) And Primary Studies On Resistance Mechanism

The resistance of the field populations of the green apple aphid (Aphis citricola von der goot) from Xinzhou, Jinzhong, Yuncheng regions of Shanxi Province to insecticides was tested. Based on the studies of the effect of synergists and biochemical studies, omethoate-resistant, fenvalerate-resistant and methomyl-resistant mechanism was discussed. The selective toxicity studies of insecticides to the ladybird beetle (Coccinella septempunctala) and aphids and test to control of the field aphids with several insecticides were also carried out. In addition, resistance management for the green apple aphid was suggested.The susceptibility of the green apple aphid from three regions to insecticides was tested with topical application recommended by FAO. Based on LD50 values, the result showed that the order of susceptibility of Xinzhou strain to commonly used insecticides was avermectin > imidacloprid > beta-cypermethrin > lambdacyhalothrin > deltamethrin > cyfluthrin > fenpropathrin > cypermethrin > fenvalerate > methomyl > omethoate > fenitrothion > malathion > isocabophos > dichlorvos; that of Jinzhong strain was beta-cypermethrin > avermectin > lambdacyhalothrin > imidacloprid > cyfluthrin > fenpropathrin > cypermethrin> deltamethrin > fenvalerate > methomyl > omethoate > malathion > dichlorvos > fenitrothion > isocabophos; and that of Yuncheng strain was avermectin > beta-cypermethrin> imidacloprid > methomyl > lambdacyhalothrin > omethoate > cyfluthrin > deltamethrin > cypermethrin > dichlorvos > fenvalerate > fenitrothion > malathion > fenpropathrin > isocabophos. The susceptibility of the Xinzhou and Yuncheng strains to avermectin was the highest and of the Jinzhong strain to beta-cypermethrin was the highest.The results indicated that the adult females of Xinzhou strain had developed low level of resistance to fenpropathrin (6.76-fold) and moderate level of resistance to isocabophos (11.96-fold); and Jinzhong strain had developed low level of resistance to deltamethrin (6.21-fold) and also moderate level of resistance to isocabophos (16.28-fold). However the aphid population of Yuncheng strain had developed low level of resistance to omethoate (5.78-fold); moderate levels of resistance to deltamethrin, cyfluthrin and fenvalerate (28.10-~ 41.85-fold) and high level of resistance to isocabophos (63.68-fold) and fenpropathrin(236.09-fold). Three green apple aphid strains are all still susceptible to avermectin, imidacloprid and beta-cypennethrin.Studies on the effect of synergists on the toxicity of commonly used insecticides to resistant aphids and biochemical studies indicated that mixed function oxidase (MFO) system may be the major enzyme systems involved in the detoxification of omethoate, fenvalerate and methomyl. Reduced penetration of insecticides also contributed to the omethoate-resistance. In addition, the resistance of the green apple aphid may be related to the increased activities of the enzyme systems including carboxylesterase (CarE) and glutathion-s- transferase (GST) and possibly acetylcholinesterase (AChE) insensitivity. Therefore, the activities of detoxification enzyme systems were important mechanism of the green apple aphid resistance to insecticides.The selective toxicity of insecticides to the ladybird beetle and aphid indicated that among the commonly used insecticides imidacloprid was most safe to predator the larvae of the ladybird beetle whereas organophosphates and pyrethroids were less safe. And maiathrin and cyfluthrin had more high selectivity than other organophosphates and pyrethroids. Therefore avermectin was highly toxic to predator though the green apple aphid was most susceptible to it.The results of test to control the field aphids with several insecticides showed that carbosulfan, imidacloprid, avermectins and phoxim+methomyl all had high efficacy. So we suggest that these insecticides can be treated as alternatives for the insecticides that had caused less susceptibility and resistance in the green apple aphids.Based on the resistance moni...