Molecular basis of spinosyn resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae): Implications for resistance monitoring and management

Gaining insight into the molecular basis of insecticide resistance evolution enables the development of sustainable pest control and long-term resistance management strategies. Here, we employed molecular approaches to investigate the mechanisms underlying spinetoram resistance in Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), a major polyphagous pest of key crops worldwide. Using bulk segregant analysis and DNA sequencing, we identified a triplet deletion (Y232del) in the α6 subunit of the nicotinic acetylcholine receptor (nAChR) gene, resulting in the loss of a tyrosine residue in an autosomal and incompletely recessive strain of S. frugiperda resistant to spinetoram. We subsequently performed backcrosses and genotyped susceptible, heterozygous and resistant individuals after exposure to a discriminating concentration of spinetoram to demonstrate the association between Y232del and insecticide resistance. Additionally, a complementation test was conducted to evaluate the presence of the same mutation in a spinosad resistant strain of S. frugiperda, using reciprocal crosses between the two resistant strains followed by progeny selection. These experiments revealed a co-segregation of Y232del with spinetoram resistance and confirmed the presence of cross-resistance to spinosyn insecticides. To translate these findings into practical monitoring tools, we screened the presence of Y232del in field-collected populations by combining genotypic screening with phenotypic bioassays. These findings support the development of molecular diagnostic tools for the accurate detection of spinosyn resistance in S. frugiperda, using Y232del as a molecular marker to inform more effective insecticide resistance management strategies.