Identification and Expression Patterns of Opsin Genes in a Forest Insect, Dendrolimus punctatus

Dendrolimus punctatus walker (Lepidoptera: Lasiocampidae) is the most serious coniferous forest defoliator in China. This species has long life history, and shows different activity rhythms and light response behaviors at larval and adult stages. Insect vision system play important roles for survival and reproduction, and disturbance of photoreception may help us to control this pest. However, we know little about the visual system of D. punctatus. As opsins are the most important genes determining photoreceptor sensitivity of insects, we identified opsins of D. punctatus and analyzed their expression patterns at different development stages in this study. Four opsin genes were identified based on our transcriptome data. Phylogenetic analysis showed that there are three classical ultraviolet (UV), blue, and long-wavelength (LW) light sensitive opsin genes, and another UV-like opsin as homolog of a circadian photoreceptor, Rh7, in Drosophila melanogaster and other insects. Expression analysis indicated that the UV and UV-like opsins expression levels only fluctuated slightly during whole life stages of D. punctatus, while Blue and LW opsins were up-regulated many times at adult stage. Interestingly, the ratio of UV-opsin was much higher in eggs and larvae stages, and lower in pupa and adult stages; reversely, LW-opsin showed extremely high relative ratio in pupa and adult stages. High expression level of LW opsin in the adult stage may correlate to the nocturnal lifestyles of this species at adult stage, and different ratios of UV and LW opsins in larval and adult stages may help to explain the different visual ecologies of these two development stages of D. punctatus. This work is the foundation for further research of opsin functions and vision mechanisms of D. punctatus.