Light traps are widely utilized to monitor and manage insect pest populations. In late 2018, the fall armyworm (FAW), Spodoptera frugiperda, invaded China through Yunnan Province representing a huge threat to grain production. To estimate the efficiency of light traps on FAW moths, we first identified the opsin genes from FAW by using the transcriptome. Phylogenetic analysis indicated that the four opsins of FAW were clustered with those of other Noctuidae species. The expressed levels of opsins in S. frugiperda were lower than in Helicoverpa armigera, suggesting a different phototactic response between the two species. Then, we determined the phototactic behavior of FAW using H. armigera as a control, which is widely monitored and managed using light traps in China. Our results indicated that the two moths species showed significantly different phototactic behavior and both female and male FAW displayed faster flight-to-light speed than H. armigera. This may be due to a faster flight capacity in FAW compared to H. armigera. However, the capture rate of both female and male of S. frugiperda was significantly lower than that of H. armigera, which was consistent with the expression levels of opsins. These results support the positive phototaxis of S. frugiperda moths and suggest light traps could be used for monitoring and managing the pests, but with a lower efficiency than H. armigera.
