Identification of Spodoptera frugiperda (Lepidoptera: Noctuidae) and its two host strains in China by PCR-RFLP

The fall armyworm (FAW) Spodoptera frugiperda was first found in China in 2018. In other countries, FAW has evolved corn and rice strain biotypes. It is not possible to identify these strains based on morphology. In addition, FAW is very similar in appearance to several other common pests. These situations bring great challenges to the population management of FAW. In this study, we developed a rapid identification method based on PCR-RFLP to distinguish the two FAW strains and the FAW from other lepidopteran pests. A 697 bp mitochondrial cytochrome c oxidase I (COI) was cloned and sequenced from FAW, Spodoptera litura, Spodoptera exigua, and Mythimna separata. The COI fragments of these species revealed unique digestion patterns created by three enzymes (Tail, AlWN I, and BstY II). Thus, these four species can be distinguished from each other. The enzyme Ban I recognized a unique SNP site on a 638 bp triosephosphate isomerase (Tpi) fragment of the corn strain FAW. The Tpi fragment of the corn strain was cut into two bands. However, the rice strain could not be digested. Using this method, all 28 FAW samples collected from different host plants and locations in China were identified as the corn strain. This suggests that the rice strain has not yet invaded China. This method allows discrimination of FAW from other Lepidopteran pests and distinguishes the two FAW host strains.

Automated summary

A rapid identification method based on PCR-RFLP was developed to distinguish the two strains of FAW and other lepidopteran pests. The unique digestion patterns of four species, including FAW, were revealed by sequencing their mitochondrial COI genes. Furthermore, a specific SNP site was found in the corn strain FAW, allowing its distinction from the rice strain. Testing 28 FAW samples collected from different locations and host plants in China confirmed the presence of the corn strain only, indicating that the rice strain has not invaded China yet. This method enables differentiation of FAW from other lepidopteran pests and identification of the two FAW host strains.