Occurrence patterns and insecticide resistance analysis of citrus psyllid in different regions of Guangxi

To analyze the occurrence patterns and insecticide resistance levels of citrus psyllids in Guangxi, this study integrated meteorological data to examine the annual fluctuations of psyllid populations in northern, central, and southern Guangxi. The resistance ratios of adult psyllids to conventional pesticides in various areas were assessed using a combination of bioassays, including the "leaf dipping method" and the "drug film method". The survey results revealed that psyllids were mainly present in northern Guangxi and central Guangxi from April to November, with average monthly temperature ranging from 18.7 to 29.6℃. During this period, the population density ranges from 128 to 643 individuals per 100 shoots. In southern Guangxi, psyllids were predominantly observed from March to November, with average monthly temperature between 20.7 and 29℃, and a population size of 136 to 860 individuals per 100 shoots. The population size of psyllids in the three regions were positively correlated with temperature, with an inflection point for population growth at approximately 19℃. Throughout the year, there were three peak periods of psyllid occurrence. In northern Guangxi and central Guangxi, the peak periods were in May, August, and September. In southern Guangxi, the peak period was in April, July, and August, one month earlier than in the other two regions. Correlation analysis between rainfall and psyllid populations revealed that during the main occurrence period, when the monthly rainfall fell into three distinct categories—0~25 mm (dry), 25~100 mm (wet) and > 100 mm (damp)—the population numbers were 258, 344 and 295 head/100 shoots in north, 219, 404 and 311 head/100 shoots in central, and 244, 435 and 355 head/100 shoots in south. The population of Psyllid in all three regions showed the trend of wet month > damp month > dry month, though the correlation was not statistically significant. Insecticide resistance monitoring results revealed that the resistance ratios of psyllid populations to imidacloprid in Northern and Southern Guangxi were 38.80 and 21.47 respectively, indicating medium resistance, while that in central regions was 94.51, indicating high resistance. The resistance ratios to thiamethoxam in the three regions were 4.04 (northern), 3.91 (central) and 1.64 (southern), respectively, indicating sensitive. The resistance ratios to chlorpyrifos in the northern and central regions were 48.09 and 50.79, respectively, with high resistance, and the south were 14.25, indicating medium resistance. The resistance ratios to cypermethrin in central and southern Guangxi were 70.71 and 60.48 respectively, with high resistance, and the north was 17.25, indicating medium resistance. In conclusion, it is recommended to rotate the application of low-resistant insecticides in the field and control the population as early as possible before the main occurrence period of psyllids.