Vision contributes to mate location in a diurnal moth: evidence from behaviour and opsin functions

Diurnal moths are active during daylight hours, yet direct experimental evidence testing the contribution of visual cues in mate location and their underlying molecular mechanisms remains limited. Using Phauda flammans , a diurnal moth with conspicuous body coloration and close-range courtship behaviours, as a model insect, we carried out a series of experiments to investigate the visual detection distance, the role of body colour and the functions of opsin genes in mate location. We found that P. flammans could detect their mates up to 30 cm away. Compared with blinded males and females, whose compound eyes were smeared with melanin, sighted adults with normal vision were more likely to locate dead, resin-coated moths of the opposite sex, suggesting that body colour and vision, rather than olfactory cues, played important roles in mate detection and recognition. We further quantified the expression of three visual opsin genes, short-wavelength ( PfSW ), long-wavelength ( PfLW ), and ultraviolet-sensitive ( PfUV ), and found that these were predominantly expressed in the adult's head, consistent with their functions in the compound eyes. A dsRNA injection of PfLW and PfUV , but not PfSW , significantly decreased mate location success, suggesting that long- and UV-wavelength photoreception is required for detecting body-reflected light during courtship. This study provides the first demonstration that visual opsin genes are involved in mate location in a diurnal moth, offering novel insights into the visual-based mate location strategies of diurnal insects.