Resistance and metabolic pathway of Spodoptera frugiperda population to beta cypermethrin in Sichuan

Objective To investigate the resistance and metabolic pathways of beta cypermethrin in fall armyworm (Spodoptera frugiperda) populations in Sichuan.

Method The resistance levels of fall armyworm to beta cypermethrin in MY, DC, CX, HD and RH populations in Sichuan were determined by drip method. The activities and gene expressions of three kinds of detoxification metabolic enzymes, such as cytochrome P450 enzymes (P450s), carboxylesterases (CarE) and glutathione S-transferase (GST), were determined by photoelectric colorimetric method and RT-qPCR. The Pearson correlation coefficient was used to analyze the correlation of beta cypermethrin resistance with enzyme activity and gene expressions. The differences in beta cypermethrin metabolic products between the MY population treated with LD₅₀ beta cypermethrin (the experimental group) and the untreated MY population (the control group) were analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS).

Result The MY population showed the highest resistance ratio (RR) to beta cypermethrin, the RR was 4.02 times and the LD₅₀ was 84.201 μg/g. The activities of CarE, GST and P450s increased with the increase of beta cypermethrin resistance, and the expression levels of CES12, GST epsilon9 and CYP6B50 genes were significantly up-regulated and significantly correlated with beta cypermethrin resistance. The metabolism differential products in the control group and the experimental group were 3-phenoxybenzoic acid (3-PBA), pyrocatechol, capric acid, methyl-2, 3-dihydro-3, 5-dihydroxy-2-oxo-3-indoleacetic acid. Among them, 3-PBA was only detected in the experimental group and not in the control group. It was inferred that beta cypermethrin was metabolized into 3-PBA through the enzyme activity of fall armyworm, 3-PBA was catalyzed by monooxygenase, two hydroxyl groups were introduced into benzene ring, and then pyrocatechol was finally generated.

Conclusion Spodoptera frugiperda may up-regulate the expression of genes associated with detoxification enzymes, leading to increased enzyme activities. This enhanced detoxification capacity accelerates the metabolic degradation of beta cypermethrin, thereby reducing the pesticide’s efficacy.