Cinnabar-dependent eye pigmentation mediates light input for circadian behavior synchronization in Spodoptera frugiperda

The fall armyworm, Spodoptera frugiperda, is a key lepidopteran pest of numerous agricultural and industrial crops worldwide. The effects of environmental factors, such as light, on the behavior of the fall armyworm have been poorly studied. Here, in this study, CRISPR/Cas9 was employed to generate a germline knockout of the eye color genes, cinnabar and cardinal. The homozygous cinnabar mutants (cin^−/−) initially exhibited a pale-yellow eye phenotype, which gradually deepened to red over time, while wild-type with black compound eyes. The cin^−/− were used for behavioral observations, indicating that adult mutants exhibited abnormal rhythmic patterns in eclosion, mating, and oviposition behaviors, suggesting that rhythmicity was significantly disrupted due to the loss of eye pigmentation. At two days post-eclosion observation of paraffin sections revealed that the pigment in the compound eye almost completely disappeared. Further, real-time quantitative PCR revealed that the expression of photosensitive and rhythm genes was completely disordered. These findings showed that the presence of cinnabar is essential for the color of the compound eye and is necessary for the fall armyworm to adjust the rhythms by sensing light through compound eye pigmentation, providing new insights into the relationship between eye and circadian rhythms in insects.