Analysis of seasonal and annual field-evolved insecticide resistance in populations of Thrips hawaiiensis in banana orchards

Every season over the past decade, efficacious thrips insecticides have been commonly applied for control of Thrips hawaiiensis on banana crops in China. For effective thrips control, some insecticides have been used extensively against the thrips in numerous banana plantations. This study aims to examine the current resistance status and the dynamics regarding the changing frequencies of resistance in the field T. hawaiiensis populations. A total of 13 field samples from banana orchards (Chengmai, Lingao, Dongfang and Ledong located in Hainan Province, China) were collected monthly in 2014 to 2017, and selected individuals were used in bioassays assessing insecticide resistance and metabolic enzyme activity compared to a laboratory-susceptible strain. In 2014, the initial resistance survey found that all sampled populations were susceptible to spirotetramat and cyantraniliprole, while Lingao and Chengmai population showed a moderate resistance to imidacloprid, acetamiprid, abamectin and spinetoram. Further, seasonal and annual analysis of resistance dynamics with imidacloprid, abamectin and spinetoram demonstrated that resistance in field populations of T. hawaiiensis developed quickly within a season (from April to August 2016), but resistance was unstable over subsequent seasons (April 2015, 2016 and 2017). Moreover, synergism experiments using enzyme inhibitors together with metabolic enzyme assays revealed that field-evolved insecticide resistance in T. hawaiiensis was closely associated with the elevated metabolic enzymes. The observed resistance increase within a season was attributed mainly to the intense use of these insecticides and short generation time of thrips. These findings suggest that a rotation system using efficacious thrips insecticides should be implemented for sustainable thrips control to reduce the potential of resistance development.