Resistance Monitoring And Population Dynamics Of Panonychus Ulmi In Apple Orchards Of Guanzhong Region In Shaanxi Province

Panonychus ulmi(Koch) is an important mite which damages apple and other fruit trees by sap-sucking worldwide. Currently, control of this mite mainly relies on chemical control. With the intensive use of acaricides, P. ulmi developed resistance to different acaricides. Knowledge of population dynamic patterns of P. ulmi is of importance for understanding the development and control of the pest, which can contribute to improving quality and yield of apple fruits. Shaanxi Province is one of the most important apple growing areas in China, and most apple trees are planted in Guanzhong region in this Province. In the study, we analyzed the toxicity and the relative resistance level of P. ulmi field populations to different acaricides in five locations of Guanzhong region in Shaanxi Province. The population dynamics of P. ulmi in three locations of Guanzhong region were also investigated to provide the basis for the IPM of P. ulmi.1. Toxicity of different acaricides to the P. ulmi field populationsThe slide-dip method was used to test the toxicity of four acaricides to the P. ulmi field populations collected from apple orchards in Xingping, Liquan, Chunhua, Fufeng and Fengxiang of Guanzhong region. The results showed that the Liquan population had the lowest LC50 for abamectin(0.041 mg/L) and thiamethoxam(58.578 mg/L), and Fengxiang population had the lowest LC50 for pyridaben(11.202 mg/L) and azocyclotin(96.181 mg/L). All the five populations showed high LC50 value to azocyclotin.2. Resistance monitoring of field populations to different acaricidesThe five P. ulmi populations varied in relative resistance level to the four acaricides tested, indicating by different LC50 values. Xingping population showed the highest LC50 value to pyridaben, and Fengxiang population showed the highest LC50 value to thiamethoxam.3. Population dynamics of P. ulmi in apple orchardsUpon analysis of the field population dynamics of P. ulmi collected from apple orchards in Xingping, Liquan and Fufeng of Shaanxi Province, the results showed that the population peaks of P. ulmi appeared in mid-June to mid-July. The population quantity of P. ulmi at different directions of apple tree was not significantly different.4. Spatial distribution pattern of P. ulmi in apple treeResults of spatiotemporal dynamics analysis indicated the spatial distribution pattern of P. ulmi belonged to the aggregated distribution pattern and uniform distribution pattern. The population was distributed in individual colonies. Its aggregation intensity was kept in a higher level at the west and north of tree crowns. The diffusion tendency of P. ulmi spread from flock to diffusion, re-diffusion and re-aggregation. The aggregation intensity of P. ulmi showed the characteristics of high population density but low patchiness density, or low population density but high patchiness density.