Susceptibility Dynamics Of Aphis Citricola Von Der Goot To Insecticides And Resistance Management Strategy

Use the bioassay and biochemical methods, the susceptibility dynamics to insecticides of different Aphis citricola von der Goot was studied, and the synergism between different mechanism insecticides to the green apple aphid was evaluated. 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 variation of the green apple aphids to various pesticides between 2000 and 2004 showed that toxicity of pesticides 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, deltamethrin significantly increased.2. The results of susceptibility variation of green apple aphids in same region to insecticides.2.1 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.2.2 The field populations from moantanious 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.2.3 he susceptibility of the aphid fed on different host plant to imidacloprid, malathion, deltamethrin, methomyl was simultaneously different. The results also demonstrated that susceptibility of the aphid fed on different apple cultivars to the same insecticide' was significantly different.The susceptibility difference of green apple aphids to insecticides among different host and different apple species have reached significant level3. 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 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.4. The joint toxicity tests of combinations between different class insecticides to the green apple aphids demonstrated that deltamethrin mixed with malathion in 1:9(a.i), imidacloprid with malathion in 1:10 or 1:15, and acetaniprid with malathion in 1:10 or 1:15 all had obvious synergism to the pest than used alone.5. Bioassay to selective toxicities of commonly used insecticides between ladybird and aphids showed that phoxim, abamectin had highest selectivity, followed by acetaniprid, fenvalerate, methomyl and imidacloprid, whereas the selectivity of omethoate and deltamethrin was lowest. Therefore, it was suggested that fenvalerate, phoxim, imidacloprid should be chosen for control aphids when there were abundant adults of ladybird in the field, but while majority of ladybird in larval period, fenvalerate, phoxim, abamectin should be used. Although acetaniprid had higher selectivity, it also was most toxic to the natural...