Multi-colored traps can enhance monitoring programs for native and non-native longhorn beetles in forest ecosystems

Longhorn beetles (Coleoptera: Cerambycidae) are one of the most diverse families of beetles worldwide and they play critical roles in forest environments. Monitoring longhorn beetles is essential for both conservation and pest management, and baited traps are widely used for this purpose. Longhorn beetle species vary in their visual ecology and are attracted to different trap colors. A way to optimize trapping efficiency could be to combine multiple colors on a single trap, so to create a trap that captures multiple species at once. To test this approach, we carried out seven trapping experiments in Europe and North America, comparing the effectiveness of a multi-colored trap against single-colored black, red, white, and yellow traps at whole family, subfamily, and species level. At most sites, multi-colored traps captured significantly more species and individuals than black, red, and/or yellow traps. At the subfamily level, at most sites, multi-colored traps were equally or more effective than single-colored traps for Cerambycinae and Lamiinae. For Lepturinae, multi-colored traps were generally significantly more effective than black or red traps, but significantly less effective than white traps. Responses varied among species. Overall, our study suggests that the use of multi-colored traps can improve monitoring programs for longhorn beetles, supporting both faunistic surveys and early detection efforts targeting non-native species.