Reproductive interference by alien hornet Vespa velutina threatens the native populations of Vespa simillima in Japan.

The yellow-legged hornet Vespa velutina has become one of the major alien species in European and East Asian countries. As in its homeland, the invading V. velutina is reported as the major predator of honeybees and is becoming a threat to beekeeping in Europe. However, it remains unknown how V. velutina might affect native hornets when it invades Asia, where a large number of Vespa species are distributed. Thus, by analyzing the mitochondrial cytochrome c oxidase subunit I gene, we investigated whether interspecific mating occurs between V. velutina and Japanese native Vespa spp. Our results showed that the alien V. velutina causes reproductive interference in Japanese native hornet Vespa simillima. Forty-three percent of native V. simillima queens had the sperm of V. velutina males, and among the all V. simillima queens analyzed, 28% only had V. velutina sperm. We did not find evidence of V. velutina queens having the sperm of V. simillima males. These findings suggest that reproductive interference by V. velutina males poses a threat to the native V. simillima populations. A decline of V. simillima may also negatively affect other insects that interact with V. simillima.