Phototaxis is widely utilized to monitor and control pest populations in agricultural practices. Tea weevil (Myllocerinus aurolineatus) is a server regional outbreak tea pest in Chinese tea plantations, and its control currently relies heavily on chemical pesticides. Previous studies have shown that adults of M. aurolineatus exhibit strong phototaxis at night.

To lay basis for developing light-based management strategies, this study clarified the effects of different light spectra on the phototactic behavior of male and female M. aurolineatus, and further revealed the regulatory effects of different light stimuli on the transcriptional expression of their opsin genes.

Firstly, to reveal the phototactic characteristic of this pest, phototaxis of female and male adult M. aurolineatus to eight types of monochromatic light was tested through behavioral choice experiments. Subsequently, bioinformatic analysis was performed to identify opsin genes in M. aurolineatus, and a phylogenetic tree of identified opsins along with those from other insect species was constructed using the neighbor-joining method. Finally, the spatiotemporal expression profiles of opsin genes were examined across different developmental stages, under circadian rhythm, and various light stimuli using quantitative real-time PCR (RT-qPCR).

Behavioral assays revealed that violet light elicited the highest attractiveness to males and was the second preferred wavelength for females, surpassed only by red light. In contrast, the blue light was the least attractive to both sexes. Moreover, the phototaxis rates of males to yellow, green and blue light were significantly higher than those of females. Bioinformatic analysis showed M. aurolineatus contains only two opsin genes, a long-wavelength-sensitive opsin (Ma-LW) and an ultraviolet-sensitive opsin (Ma-UV); no blue-light-sensitive opsin gene was detected, which was in accordance with the lowest phototactic rate to blue light observed in behavioral assays. Spatiotemporal expression profiling showed that both Ma-LW and Ma-UV were highly expressed in adults, with no significant difference throughout the light-dark cycle. Furthermore, dark adaptation up-regulated both Ma-LW and Ma-UV expression in M. aurolineatus adults, while subsequent short-term light stimuli (red, blue and violet) significantly reversed this up-regulation. Among these, red light exerted significantly stronger suppressive effect on Ma-LW expressional abundance than blue or violet light, while no significant difference in suppressive effect on Ma-UV expression was detected among the three lights.

Sexual dimorphism is evident in the phototactic behavior of adult M. aurolineatus, and exposure to different light spectra can down-regulate opsin gene transcription in dark-adapted M. aurolineatus, these findings contribute to the development of light-based M. aurolineatus management strategies.