Induction of colony initiation by Japanese native bumble bees using cocoons of the exotic bumblebee Bombus terrestris

The colony initiation rates of Bombus hypocrita (a native Japanese bumblebee) and Bombus terrestris (a European species) foundresses were compared after 4 weeks of exposure to B. terrestris cocoons. The B. terrestris cocoons, when replaced weekly, were effective for inducing oviposition by foundresses of both species. There were no significant differences in the colony initiation rates of B. terrestris and B. hypocrita, either with the control treatment or with the cocoons. The cocoon method was also tested for five species and two subspecies of native Japanese bumblebees. The colony initiation rate was higher for foundresses of the subgenus Bombus s. str. than for foundresses of the subgenera Pyrobombus, Diversobombus, and Thoracobombus. When replaced weekly, the cocoons of B. terrestris are effective inducers of colony foundation in three Japanese native species, namely B. ignitus, B. hypocrita hypocrita, and B. h. sapporoensis.