The Life History and Pollination Ecology of Bumblebees in the Alpine Zone of Central Japan

We studied the life history and pollination ecology of bumblebees in the alpine (2600-2800m a.s.l.) and subalpine (1500-2400m a.s.l.) zones of Mt. Norikura in central Honshu, Japan. Bombus beaticola was the only species that nested in the alpine zone, where the nests seemed to have produced few reproductive bees. Their main nest sites were probably in the subalpine zone. Bombus hypocrita workers also foraged in the alpine zone. Some foraging workers of B. beaticola moved between subalpine and alpine sites, and the mean size of foraging workers in the alpine zone was larger than that in the subalpine zone throughout mid summer. This suggested that larger workers from the subalpine colonies foraged in the alpine zone. In alpine flowers utilized mainly by bumblebees, fruiting rates were significantly decreased when insect pollinators were excluded by bagging, and flowers blooming at the beginning and the end of the season had lower fruiting rates probably because of the reduced numbers of bumblebee-pollinators. Thus, although bumblebees may not complete their life-cycles in the alpine zone, they maintain mutual relationships with alpine flowers through the foraging activity of workers from subalpine and alpine colonies.