| Summary: | Abstract The rapid naturalization of Bombus terrestris across the Nemuro Peninsula has led to a decline in two closely related native Japanese species, namely Bombus hypocrita sapporensis and Bombus cryptarum florilegus, both belonging to the common subgenus Bombus. Although it is widely believed that cross-mating of native and non-native species is influenced by the common male sex pheromone in this region, no study has been conducted to substantiate this claim. Thus, we investigated the cross-activities of male sex pheromones between native and non-native bumblebees, as well as the frequencies of cross-mating, using chemical and DNA assays. Our gas chromatography–electroantennographic detector analyses and behavioral tests revealed the presence of sex pheromonal cross-activities between B. terrestris and the two Japanese bumblebees species. Furthermore, DNA analyses revealed the occurrence of cross-mating between native and non-native species in the Nemuro Peninsula. Overall, these results indicate the immediate need for conservation measures to safeguard Japanese bumblebee populations in the Nemuro Peninsula.
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