| The resistance monitoring in the green apple aphid, Aphis citricola von der Goot, and the hawthorn spider mites, Tetranychus viennensis Zacher, collected from different locations in Shanxi and in different years, to commonly used pesticides were conducted. Based on the monitoring data, the effect of host plants on the susceptibility of the green apple aphid to insecticides were determined, and the resistance mechanism of the two pests to pesticide were primarily studied using different synergists and through analysis of various detoxication enzymes. The selective toxicity of commonly used insecticides between ladybird, Coccinella septempunctata L and the green apple aphid were also evaluated, and integrated management strategies of pesticide resistance in these two pests were also discussed. The main results were as following:1. The susceptibility of hawthorn spider mites from Xinzhou, Jinzhong and Yuncheng regions of Shanxi to acaricides was determined with slide-dip method recommended by FAO. The results showed that the susceptibility order of Xinzhou strain was abamctin > pridabe > fenpropathrin > dicofol > amitraz > azocyclotin> isocarbophos > chlorpyrifos > fenbutatin oxide > clofentenzine, and that of Jinzhong strain was abamctin > azocyclotin > fenpropathrin >dicofol > pridaben > chlorpyrifos > amitraz > fenbutatin oxide > isocarbophos > clofentenzine, whereas the susceptibility order of Yuncheng strain was abamctin > fenpropathin > azocyclotin > amitraz > pridaben > fenbutatin oxide > chlorpyrifos > isocarbophos > clofentenzine > dicofol. The susceptibility of three strains to abamectin was the highest. The results indicated that Xinzhou strain had developed low-level resistance to isocarbophos and chlorpyrifos (7.74 and 5.35-fold), moderate-level resistance to fenpropathrin and dicofol (17.79 and 31.93-fold), the Jinzhong and Yuncheng strains had developed low-level resistance to amitraz (6.70 and 5.64-fold) and pridaben (5.16 and 6.89-fold). The Jinzhong strain had developed middle-level resistance to isocarbophos, fenpropathrin and dicofol (22.42 to 33.00-fold). The Yuncheng strain had high-level resistance to isocarbophos, fenpropathrin and dicofol (41.53 to 1714.01-fold), middle-level resistance to chlorpyrifos (34.49-fold). The results also showed that the three strains remained susceptible to abamectin, azocyclotin, clofentenzine and fenbutatin oxide.2. The susceptibilities of green apple aphids from three regions to insecticides were tested with topical application. Based on LD50 values, the results showed that the susceptibility order of Xinzhou strain to insecticides was abamectin > imidacloprid > beta-cypermethrin > lambdacyhalothrin > deltamethrin > cyfluthrin> fenpropathrin > cypermethrin > fenvalerate > methomyl > omethoate > fenitrothion > malathion > isocabophos > dichlorvos, and that of Jinzhong strain was beta-cypermethrin > abamectin > lambdacyhalothrin >imidacloprid > cyfluthrin > fenpropathrin > cypermethrin > deltamethrin > fenvalerate > methomyl > omethoate > malathion > dichlorvos > fenitrothion > isocabophos; whereas the susceptibility order of Yuncheng strain was abamectin > beta-cypermethrin > imidacloprid > methomyl > lambdacyhalothrin > omethoate > cyfluthrin > deltamethrin > cypermethrin > dichlorvos > fenvalerate > fenitrothion > malathion > fenpropathrin > isocabophos. The results indicated that Xinzhou strain had developed low-level resistance to fenpropathrin (6.76-fold) and moderate level to isocabophos (11.96-fold); Jinzhong strain had developed low-level resistance to deltamethrin (6.21-fold) and moderate level to isocabophos (16.28-fold). However, the Yuncheng strain had developed low-level resistance to omethoate (5.78-fold), moderate level to deltamethrin, cyfluthrin and fenvalerate (28.10-41.85-fold), and high-level resistance to isocabophos (63.68-fold) and fenpropathrin (236.09-fold). Three strains were all still susceptible to abamectin, imidacloprid and beta-cypermethrin.3. The susceptibility variation of the green apple aphids to various pesticides between 2000 and 2004 showed that toxicity of all pesticides tested to the pest varied greatly because of different models of pesticide application and culture styles in different regions. In Xinzhou region, malathion, deltamethrin, DDVP, beta-cypermethrin, abamectin and omethoate showed decreasing toxicity trend to the aphid, but fenvalerate, imidacloprid and methomyl showed increasing toxicity trend; The toxicity of malathion, omethoate, fenvalerate, beta-cypermethrin and imidaclopride to Jinzhong strain was declined, whereas deltamethrin, methomyl' and abamectin increased. In Yuncheng region, the susceptibility of the aphid to omethoate, beta-cypermethrin, abamectin, malathion and fenvalerate decreased, but that of methomyl, imidacloprid, deltamethr in significantly increased. The results demonstrated that the toxicity of insecticides tested fluctuated to the pest at different time of a day, but most toxic between 16:00 to 18:00pm. The field populations from mountanious orchards showed higher susceptibility to insecticides than from plain areas, and from mixture-cultivating orchards was higher than from orchard where only apple trees were planted. The susceptibility of each population to imidacloprid was the highest among four insecticides.4. The experimental results of biochemical analysis to detoxication enzyme in the aphid fed on apple, pear, plum, almond respectively, showed that activities of glutathion-S-transferase (GST), acetylcholinesterase (AChE), carboxyl esterase (CarE), mixed function oxidase (MFO) was highest in the aphid on apple, followed by pear, plum and almond. The activity of each enzyme in different aphid strains were significantly different (p< 0.05 or 0.01), these results indicated that host plants could obviously affect the activities of detoxification enzymes in the body of aphids. The susceptibility of the aphid fed on different host plant to imidacloprid, malathion, deltamethrin, methomyl was simultaneously different, and the susceptibility to each pesticide and the activity of each enzyme showed negative relationship, this indicated that raise of detoxification enzyme activities was important mechanism of insecticidal resistance in the green apple aphids. The results also demonstrated that...
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