The development of insecticide resistance in insect populations is a major challenge to sustainable agriculture and food security worldwide. Methoxyfenozide, an insect growth regulator that acts as an agonist of 20-hydroxyecdysone (20E), has severely declined in its efficacy against the rice stem borer ( Chilo suppressalis ), a notorious pest of rice crops in East and Southeast Asia. To date, however, the genes involved in methoxyfenozide resistance in target pests remain unclear. We conducted a long-term (seven years from 2017 to 2023) and large geographical scale (8 provinces and 45 cities in China) resistance monitoring program for methoxyfenozide in C. suppressalis . Resistance was seen to arise rapidly in this species, with >100-fold resistance being detected in nearly all the field populations after 2018 . Piperonyl butoxide (PBO), an inhibitor of cytochrome P450 enzymes (P450s), significantly increased the sensitivity of resistant strains of C. suppressalis to methoxyfenozide, implicating P450s in resistance. Six P450 genes: CYP321F3, CYP6CV5, CYP9A68 , CYP6AB45, CYP324A12 and CYP6SN2 were identified as highly expressed in resistant C. suppressalis by transcriptome profiling. Of these, ectopic expression of CYP321F3 in Drosophila melanogaster resulted in a 7.0-fold increase in resistance to methoxyfenozide demonstrating its causal role in resistance. Collectively, these findings provide insight into the mechanisms mediating resistance to insect growth regulators and will inform the development of future pest and resistance management strategies.
Chilo suppressalis Walker (Lepidoptera: Crambidae) is a widely destructive pest occurring in rice, particularly in the rice-growing regions of Asia. In recent years, C. suppressalis has developed resistance to several insecticides because of the extensive use of insecticides. The resistance levels to four insecticides were determined among populations from different regions of Sichuan Province, China, using a drop-method bioassay. Based on LC 50 values of a laboratory susceptible strain, all field populations showed moderate level of resistance to triazophos (23.9- to 83.5-fold) and were either susceptible or had a low level of resistance to abamectin (2.1- to 5.8-fold). All field-collected populations had a low or moderate level of resistance to chlorpyrifos (1.7- to 47.1-fold) and monosultap (2.7- to 13.5-fold). The synergism experiment indicated that the resistance of the XW19 to triazophos may be associated with cytochrome P450 monooxygenases (P450s), with the highest synergistic ratio (SR) of 3.05-fold and increased ratio (IR) of 2.28-fold for piperonylbutoxide (PBO). The P450 activity of the TJ19 population was the greatest among the six field populations. Moreover, the relative expression levels of four resistance-related P450 genes were detected with qRT-PCR, and the results indicated that CYP324A12 , CYP321F3 and CYP9A68 were overexpressed in the resistant population, especially in the XW19 population (by 1.2-, 3.4 -, and 18.0-fold, respectively). In addition, the relative expression levels of CYP9A68 among the CZ19 and TJ19 populations were also enhanced 10.5- and 24.9-fold, respectively. These results suggested that CYP324A12 , CYP321F3 and CYP9A68 may be related to the resistance development of C. suppressalis to triazophos.
危险品化学品经营许可证（带存储）