Victims of the cure: Determining the pollinator and necrophage biodiversity costs of Japanese beetle [Popillia japonica] traps

Trapping of the Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), a highly invasive beetle, is a widely used monitoring and pest control strategy in North America. However, these traps frequently capture nontarget beneficial insects such as pollinators and necrophages, raising conservation concerns. In this study, we quantified the abundance and diversity of bees (Apidae: Apis mellifera, Bombus spp.) and carrion beetles (Coleoptera: Staphylinidae) inadvertently collected in baited traps across 20 farms along an agricultural intensification gradient in southern Québec, Canada. Using 360 trap samples collected between June and September 2024, we analyzed how bycatch varied with seasonality, Japanese beetle abundance, landscape composition, and weather conditions. We found that pollinator bycatch was higher early in the season and in farms with either highly intensive crops or mostly natural land covers and was positively influenced by high temperature and low humidity. In contrast, necrophage bycatch peaked in late August, and was abundant under cooler, rainy conditions, and mid-level agricultural intensification. Japanese beetle abundance intensified the seasonal effects on both functional groups, likely due to the release of cadaveric volatile compounds. Results suggest that baited Japanese beetle traps pose a limited but non-negligible threat to beneficial insect biodiversity. Our comprehensive bycatch assessment is used to suggest mitigation approaches to minimize unintended captures and promote conservation efforts. • Japanese beetle traps create risks for necrophage diversity, less for pollinators • Pollinator bycatch peaks early under hot and dry conditions • Necrophage bycatch peaks late under cool and rainy conditions • Bycatch patterns vary with landscape composition • Contrasting mitigation strategies force choices for preservation efforts