Genetic architecture and insecticide resistance in Chinese populations of Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda invaded China in December 2018 and has since spread quickly countrywide. Two sympatric biotype strains of FAW, rice-strain and corn-strain, have been classified and showed to have different susceptibilities to chemical insecticides. Present FAW control has primarily relied on insecticides, which resulted in a rapid evolution of the resistance to insecticides in FAW. Herein, sixteen geographical populations of FAW were collected annually from maize fields in China between 2019 and 2021, both Tpi genotyping (n = 3079) and feeding preference bioassay (n = 2892) showed Chinese FAW were predominantly the corn-strain. Resistance monitoring revealed that FAW had not evolved resistance to chlorantraniliprole since it invaded China with RRs of 0.32-2.32 and a very low mutation frequency RyR of 0.14%. Most FAW populations were susceptible to emamectin benzoate, spinetoram, indoxacarb, lambda-cyhalothrin and acephate. However, low resistance levels (5 < RR < 10) were detected in some populations, suggesting rotational or mixed applications of insecticides and further resistance monitoring must be strengthened to prevent or delay the development of insecticide resistance. The mutation frequency of ace-1 at the locus A201S and F290V was 21.27% and 84.51%, respectively. The mutation frequency of VGSC at the locus T929I and L1014F was 0.11% and 0.15%, respectively. The detoxification enzyme activities of P450s, ESTs and GSTs were relatively consistent among different populations. Our study provides a systematical understanding of the current genetic architecture and resistance status of FAW in China and will contribute to the region-wide chemical control and the development of resistance management strategies for FAW in China.

Automated summary

This study investigated the genetic architecture and resistance status of fall armyworm (FAW) in China. The findings revealed that the corn-strain of FAW was predominant in China, and some populations exhibited low levels of resistance to certain insecticides. The study also identified gene mutations with relatively high mutation frequencies. The results have significant implications for the development of region-wide chemical control and resistance management strategies for FAW in China.