Phototaxis of Exolontha castanea (Coleoptera: Melolonthidae) adults to different color light-emitting diodes (LEDs): blue-violet light preference

Exolontha castanea (Coleoptera: Melolonthidae) is a major subterranean pest of sugarcane in China, causing significant reductions in both yield and sugar content. Light trapping represents a vital strategy for monitoring and managing pest populations. With the rapid advancement of light-emitting diode (LED) spectrum technology, LEDs have increasingly replaced traditional insect-trapping light sources. This study investigated the spectral sensitivity of E. castanea adults to 14 distinct LED light sources and examined their preference behavior when presented with pairwise combinations of four sensitive wavelengths. Field experiments conducted between 2022 and 2023 evaluated the trapping efficacy of three LED light sources: ultraviolet A (UVA, 365–370 nm), blue-violet (BV, 420–425 nm), and blue (B, 450–455 nm), using solar insecticidal lamp traps targeting adults. The results indicated that both female and male adults exhibited positive phototaxis to all LED lights, with higher sensitivity to UVA, violet (V, 380–385 nm), dark violet (DV, 395–400 nm), and BV lights, characterized by elevated phototactic response rate ( R p ) and strong phototactic response rate ( R sp ). When exposed to two sensitive wavelengths simultaneously, both sexes preferred UVA, but no significant difference in R sp was observed between the paired lights. Notably, field data demonstrated BV light captured 2.5-fold more adults than UVA and B lights ( p < 0.05), with a female-biased sex ratio (most carrying eggs). Collectively, BV light proves to be the most effective attractant for E. castanea adults, suitable for both population monitoring and eco-friendly field control. • Exolontha castanea is an important subterranean pest of sugarcane in China. • The phototaxis of female and male adults are wavelength-dependent and sensitive to light sources in the range of 365–425 nm. • Blue-violet light within 420–425 nm can attract the most adults in the field. • Light trapping can be used as a field monitoring and control strategy for Exolontha castanea adults.