Reproductive disturbance of Japanese bumblebees by the introduced European bumblebee Bombus terrestris

Abstract

The European bumblebee, Bombus terrestris, is an invasive eusocial species whose distribution is expanding greatly beyond its native range because numerous colonies are imported to or locally produced in non-native countries for pollination of agricultural crops. Closely related species exist in Japan where the unrestricted import and use of B. terrestris has resulted in the establishment of wild colonies. Laboratory studies previously showed that B. terrestris and Japanese native species can copulate and produce fertilized eggs. Although these eggs do not hatch, the interspecific mating can cause a serious reproductive disturbance to native bumblebees. In this study, we determined the frequencies of interspecies mating between B. terrestris males and native bumblebee queens in the wild on the islands of Hokkaido and Honshu by analyzing the DNA sequences of spermatozoa stored in spermathecae of native queens. We found that 20.2% of B. hypocrita hypocrita queens and 30.2% of B. hypocrita sapporoensis queens had spermatozoa of B. terrestris males in their spermathecae. Given that a Bombus queen generally mates only once in her life, such high frequencies of interspecific mating with B. terrestris pose serious threats to the populations of native bumblebees in Japan.

Reproductive disturbance risks to indigenous Japanese bumblebees from introduced Bombus terrestris

“…Therefore, most crossing between introduced B. terrestris and indigenous Japanese bumblebees would not lead to diploid worker production, and any resulting colonies should collapse without production of any reproductives. As previously mentioned, Kondo et al (2009) B. terrestris and indigenous B. ignitus, B. h. hypocrita, and B. h.…”

“…This finding suggests that (1) bumblebees discriminate conspecific mating partners via male sex pheromones, and (2) the species discrimination ability of virgin gynes and males is disrupted at close range. Kondo et al (2009) (Ono, personal communication). Bombus terrestris, B. ignitus, and B. hypocrita are phylogenetically closely related (Kawakita et al, 2004;Cameron et al, 2007).…”

“…Reproductive disturbance risks to indigenous Japanese bumblebees from introduced Bombus terrestris (Kondo et al, 2009). Here, we briefly review hybrid production in light of the reproductive isolation mechanisms that have been observed in other animals, and evaluate the influences of inviable hybrid production on the reproduction of bumblebees indigenous to Japan.…”

Introduction to the Special Feature for Ecological Risk Assessment of Introduced Bumblebees: Status of the European bumblebee, Bombus terrestris, in Japan as a beneficial pollinator and an invasive alien species

“…Additionally, analysis of the DNA sequences of the spermatozoa stored in the spermathecae of native queens in Hokkaido Island and Tohoku district showed that about 30% of B. hypocrita queens had mated with B. terrestris males. Given that a Bombus queen generally mates only once in her life, these high frequencies of interspecific mating with B. terrestris pose serious threats to the populations of native bumblebees in Japan (Kondo et al, 2009;see Tsuchida et al, 2010, this issue).…”

Status of the invasion and range expansion of an introduced bumblebee, Bombus terrestris (L.), in Japan

“…Invasions of B. terrestris in Japan are particularly important when considering the impact on native ecosystems because native bumblebee species and bumblebee-pollinated plants are abundant. Indeed, ecological impacts of B. terrestris on native bumblebee populations and bumblebee-pollinated plants have been reported within invaded regions of Japan (e.g., Dohzono et al, 2008;Inoue et al, 2008;Kondo et al, 2008). Investigations on the current invasion status of B. terrestris and its relationships with environmental factors are needed to provide primary information for the evaluation of potential future ecological risks.…”