Resistance mechanisms to diamides in the soybean looper, Chrysodeixis includens

Diamides, which target insect ryanodine receptors regulating Ca²⁺ homeostasis, are among the most in-demand insecticides in the market. However, resistance to diamides has been reported in at least 17 countries and in 16 pest species, including the soybean looper (Chrysodeixis includens) (Lepidoptera: Noctuidae). This migratory pest of soybean has developed resistance to several insecticides including diamides. The resistance mechanisms that have been documented in diamide resistance include target site alteration and metabolic resistance, which are several mutations in the target sites and expressional changes in detoxification enzymes such as P450 causing enhanced metabolism of the insecticide, respectively. Yet, the specific resistance mechanisms of the soybean looper to diamides remain unclear. In our previous study, we identified a mildly resistant population to chlorantraniliprole. Here, we present that our transcriptome analysis revealed that the upregulation of detoxification enzymes such as P450 (cytochrome P450 monooxygenase) and GST (glutathione S-transferase) may contribute to the resistance, although other mechanisms, such as target site alteration, cannot be ruled out. Additionally, one of the most upregulated unigene groups in the resistant population encodes cuticle proteins, suggesting that changes in penetration rate may also play a role in the resistance. Our results indicate that diamide resistance in the soybean looper involves a combination of several resistance mechanisms. We anticipate that our study will provide new insights into the molecular basis of diamide resistance and aid in developing integrated pest management strategies.