Development of a single nucleotide polymorphism-based DNA marker for fall armyworm (Lepidoptera: Noctuidae) biotyping: a case study from the fall armyworm outbreak in Sri Lanka

Crop damage caused by fall armyworm (FAW), Spodoptera frugipera J.E. Smith (1797) (Lepidoptera: Noctuidae), has generated concern among agriculturists globally. In 2019, FAW was first reported in Sri Lanka, where it caused significant losses to corn crops. However, given that the two FAW biotypes - "rice strain" (R-FAW) and "corn strain" (C-FAW) - are morphologically identical, the biotype(s) present in Sri Lanka were unknown. The current study used the mitochondrial cytochrome c oxidase subunit I gene (mt-CO1) of FAW to biotype nine FAW samples collected in Sri Lanka. The resulting molecular phylogeny revealed that both R-FAW and C-FAW biotypes were present among the samples. In addition, we used the temperature-switch polymerase chain reaction (PCR) technique to develop a gel-based molecular marker. Two fragments were successfully amplified by the newly developed marker ABUOP0002, with fragment sizes of 341 bp from R-FAW and 204 bp from C-FAW. This demonstrates that ABUOP0002 can serve as a diagnostic gel-based molecular marker to identify the R-FAW and C-FAW biotypes from samples already identified to species level as S. frugiperda through taxonomical keys and provides a possible alternative to more expensive sequencing-based assays.