Two host‐plant strains in the fall armyworm

The fall armyworm (Spodoptera frugiperda) is one of the major pest insects damaging diverse crops including cotton, corn, rice, and sorghum. Fall armyworms have been identified as two morphologically indistinguishable strains, the corn strain, and the rice strain, named after their preferred host‐plants. Although initially recognized as host‐plant strains, there has been an ongoing debate regarding whether the corn and rice strains should be considered as such. In this article, we present arguments based on recent population genomics studies supporting that these two strains should be considered to be host‐plant strains. Furthermore, host‐plant adaptation appears to be a driving evolutionary force responsible for incipient speciation in the fall armyworm. The existence of two sympatric strains within the fall armyworm, a lepidopteran species, has been well‐documented for nearly four decades. However, the underlying evolutionary mechanism responsible for the genetic differentiation between these strains has remained a subject of intense debate. This review highlights recent evolutionary genomic studies, demonstrating the role of host‐plant adaptation as the driving force behind the incipient speciation between these strains.