Genomic divergences between the two polyphagous Spodoptera relatives provide cues for successful invasion of the fall armyworm

The fall armyworm Spodoptera frugiperda recently invaded China, ravaging crops in many provinces. Deciphering the possible genetic basics for its successful invasion is critical for innovative and specific control for this gluttonous pest. Here we generated comparative genomic analyses between S. frugiperda and its native relative, S. litura, which differs in host preference, locomotivity and production behavior. We demonstrated that S. frugiperda genes are enriched in taste sensory perception and nervous system, obviously different from those of S. litura. Potential host adaptation genes showed generally an elevated ratio of non-synonymous substitution rate to synonymous substitution rate, suggesting a faster evolution during the divergence of the two species. Focusing on these sets of genes, we identified 23 genes being under positive selection in S. frugiperda. Among them are two notable genes involved in sensory perception, gustatory receptor (GR) and an acetaldehyde oxidase, which are important for host detection in invasion and expansion processes. Another two genes are mitochondrial adenosine triphosphate synthase β subunit and ferritin heavy chain, which may be associated with the enhanced locomotivity and resistance, which fascinated long-distance migration needed for invasion and rapid expansion. Another interesting gene is chorion protein, in which positive selection sites in S. frugiperda were found and a replacement in one site is predicted to affect the protein function, which might be associated with competent reproductivity in S. frugiperda to ensure genetic resources for expansion.