Visual responses of a dominant predatory beetle, Propylaea japonica (Coleoptera: Coccinellidae), to light

Abstract

Phototaxis, a visual behaviour of insects toward light, is used to monitor and control insect pests worldwide. However, certain pest control practices have raised concerns because of the unintended elimination of non-target insects. Additionally, artificial lighting has expanded owing to urbanization. We investigated the phototactic behaviour of the dominant predatory beetle, Propylaea japonica. We explored its visual responses to seven monochromatic lights at 365–655 nm wavelength and various intensities at the preferred wavelength. The highest response occurred at 365 nm (ultraviolet), followed by 465 and 525 nm. When only the light intensity at 365 nm was varied (10, 100, and 300 lux), the response to 365 nm at 10 lux decreased, and the strongest response shifted to 420 nm (violet), but the preference increased with elevated light intensity at 365 nm. Examining behavioural responses to light intensities at 1–5000 lux (365 nm), a preference for 1000–5000 lux was observed, although mixed populations (males and females) exhibited increased responses at 10–100 lux. Our results indicate a preference for shorter wavelengths (365 nm) across different light environments (wavelength) and underscore the role of light intensity in influencing wavelength selection in P. japonica. This study provides insights for the development of light sources for insect monitoring and pest control.