Resistance Monitoring And Population Dynamics Of Aphis Citricola In Apple Orchards Of Shaanxi Province

Aphis citricola is an important insect pest in apple orchards and damages the young shoots of apple tress. Chemicals spraying is the major method to control this pest. With the intensive use of chemical insecticdes, A. citricola may develop resistance to different chemicals. In the current study, we monitored the resistance level of A. citricola collected from apple orchards in Liquan, Chunhua, Fufeng and Fengxiang regions of Shaanxi province to different insecticides. Population dynamics of A. citricola in apple orchargs of Liquan and Xingping regions was investigated. The major results are listed below:1. Populations of A. citricola from Liquan, Chunhua, Fufeng and Fengxiang showed different susceptibility to the four insecticides. Chunhua populations showed the lowest LC50(2.1769 mg/L)for abamectin; Fengxiang population showed the lowest LC50(21.4766 mg/L) for imidacloprid; Fufeng population showed the lowest LC50(32.9177 mg/L) for acetamiprid; and Liquan population showed the lowest LC50(15.8497 mg/L) for λ-Cyhalothrin.2. Populations of A. citricola from Liquan, Chunhua, Fufeng and Fengxiang showed different resistance level to the four insecticides.3. Population peaks of A. citricola in the apple growing season appeared in May and June in Xingping and Liquan regions. Population of the aphid in the two regions is lowest in July and August. In September, A. citricola can be found in the two regions in short periods, and population decreased quickly at the end of the month and then can not be found on the apple leaves afterwards.4. Populations of A. citricola in Xingping and Liquan regions belonged to the aggregated distribution pattern and uniform distribution pattern. The highest diffusion and aggregation period was May and June, indicating by the diffusion coefficients(C) and aggregation indexes(m*/m).