Simple SummaryThe Asian longhorned beetle (Anoplophora glabripennis) is an invasive species that attacks at least 209 species (or cultivars) of healthy trees. Several sex pheromones and host kairomones have been used as bites to monitorA. glabripennisin the field, but two beetles were captured by the dozens of traps at Cornuda, Italy, while no beetles were captured at Paddock wood, UK. Semiochemical-based traps have still not reached operational efficacy in the field. Therefore, an effective tool is needed for monitoring this beetle. Light traps were widely used in the monitoring and management of pest populations. However, the phototactic behavior of adults remains enigmatic. To provide a theoretical foundation to select the suitable light emitting diode (LED)-based light sources used for monitoringA. glabripennis, we first investigated the influence of exposure time and diel rhythm on the phototactic behavior of females and males to provide test conditions, and then tested effect of 14 different wavelength lights and intensity of the most preferred wavelength. Our findings show that 420 nm and 435 nm are the most suitable wavelengths for attracting adultA. glabripennisat night. This study can provide a theoretical basis for developing monitoring technologies forA. glabripennisbased on LED light traps.AbstractLight traps play a crucial role in monitoring pest populations. However, the phototactic behavior of adult Asian longhorned beetle (ALB) remains enigmatic. To provide a theoretical foundation to select the suitable light emitting diode (LED)-based light sources used for monitoring ALB, we compared the effect of exposure time on the phototactic response rates of adults at wavelengths of 365 nm, 420 nm, 435 nm, and 515 nm, and found that the phototactic rate increased gradually when the exposure time was prolonged, but there was no significant difference between different exposure times. We evaluated the effect of diel rhythm and found the highest phototactic rate at night (0:00–2:00) under 420 nm and 435 nm illumination (74–82%). Finally, we determined the phototactic behavioral response of adults to 14 different wavelengths and found both females and males showed a preference for violet wavelengths (420 nm and 435 nm). Furthermore, the effect of the light intensity experiments showed that there were no significant differences in the trapping rate between different light intensities at 120 min exposure time. Our findings demonstrate that ALB is a positively phototactic insect, showing that 420 nm and 435 nm are the most suitable wavelengths for attracting adults.