Development of a Rapid Isothermal Amplification Assay for the Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), Using Species-Specific Genomic Sequences

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), is native to tropical and subtropical regions of the Western Hemisphere, but is now regularly appearing in crop fields across South Korea, particularly in corn fields. Therefore, it is crucial to promptly and accurately identify the presence of FAW in crop fields to effectively eradicate it as a regulated quarantine species. We developed a loop-mediated isothermal amplification (LAMP) assay, which allows for rapid in-filed identification. To develop the LAMP assay, we selected FAW-specific genomic regions from the whole-genome sequences of one FAW and 13 other lepidopteran species and validated five primer sets that consistently produced positive reactions in ten FAW samples collected from eight different locations in four countries. The assay successfully identified FAW in a maximum of 45 min, starting from crude DNA extraction (~15 min) to diagnosis (30 min) from the following samples, which were deposited outdoors for 30 days: a 1st-instar larva, an adult leg, an adult antenna, and 1/16 and 1/8 of an adult thorax. The five assays can be used selectively or in combination to cross-check and provide further confidence in the in-field diagnosis of FAW.