Socio-economic effects on colony size in the bumble bee Bombus terrestris (Hymenoptera: Apidae): a thesis submitted in conformity with the requirements for the degree of Master of Science in Zoology at Massey University

Abstract

This study examined factors related to the development and eventual size of bumble bee colonies (Bombus terrestris (L).). Experiments were conducted over two seasons in both the laboratory and the field. In the first season the effect of supplementary feeding of sugar solution upon colony growth was examined. In the second season the effect of sugar feeding on worker dominance was studied.

The feeding of sugar syrup to bumble bee colonies resulted in a reduced colony size and (at the 56th day from colony initiation) greater mean ovarian development in workers. In laboratory colonies that were sugar-fed foundress queen longevity was reduced. These results were interpreted as suggesting that sugar feeding influenced colony size via an effect on the social structure of the colony. Conflict between workers and the foundress queen near the peak of colony development has been widely reported in bumble bees and my results suggested sugar feeding increased worker dominance over the queen and that this curtailed colony growth. The relationship between worker dominance and colony development was studied, using the assumption that the dominance of workers increases with their age. Colonies were manipulated by selective removal of either the oldest or youngest workers, to produce a difference in the average age of the worker populations. In colonies with a higher mean worker age there was an earlier change to sexual production and fewer workers were produced. Earlier sexual production also occured where the number of workers in a nest was artificially increased. The small size of

sugar-fed colonies was attributed to

the early appearance of

reprodutives due to a premature rise in the numbers of dominant workers. It was concluded that worker dominance was affected by trophic/economic effects such as the effort required to procure nectar, and that the provision of sugar solution in hives seems inadvisable in commercial management of bumble bees.