Reproductive disturbance risks to indigenous Japanese bumblebees from introduced Bombus terrestris

The bumblebee Bombus terrestris is not only an effective pollinator but also a potential invasive species outside its native range. Interspecific crossing of B. terrestris with indigenous B. hypocrita sapporoensis and B. ignitus can cause inviable hybrid production under laboratory conditions. Additionally, nearly 30% of B. hypocrita sapporoensis and B. hypocrita hypocrita queens are estimated to copulate with B. terrestris males in the field, suggesting that genetic deterioration of indigenous bumblebees is possible through hybridization with the introduced species. We briefly review interspecific reproductive isolation mechanisms and discuss the negative impacts of B. terrestris on the reproduction of indigenous bumblebee species in Japan due to interspecific mating.