Insecticide resistance of western flower thrips, Frankliniella occidentalis (Pergande) in China

Frankliniella occidentalis (Pergande) is a polyphagous thrips that feeds on various horticultural crops worldwide. Its unique biological properties make it highly adaptable, and it has developed resistance to various insecticides as a result. Understanding the susceptibility of F. occidentalis field populations to insecticides is necessary to select suitable agents for their control. In the present study, we tested the toxicity of eight insecticides (spinosad, spinetoram, abamectin, emamectin-benzoate, chlorfenapyr, thiamethoxam, β-cypermethrin, and broflanilide) in 21 field populations of F. occidentalis collected from 2019 to 2021. F. occidentalis has shown variable resistance to seven of these insecticides, but it is susceptible to broflanilide. Populations from Changping, Tongzhou and Yanqing in Beijing were found to be the most resistant, while those from Shunyi, Beijing and Hetian in Xinjiang were the least resistant. The population with the highest level of resistance was collected from Yanqing, Beijing; for emamectin-benzoate, the resistance ratio (RR) of this population compared to the susceptible laboratory strain of F. occidentalis was 7455.6. The overall resistance of F. occidentalis has decreased over the past three years, as demonstrated by the reduction in the proportion of highly resistant populations. This may have been due to the implementation of pesticide reduction programs and the increased use of non-chemical control methods.