Development of bumblebee colonies of Bombus bellicosus and Bombus pauloensis under two nutritional diets

Abstract

Bumblebees of the genus Bombus are excellent pollinators that contribute to the maintenance of natural ecosystems and agricultural production. Uruguay has two native species, Bombus bellicosus and Bombus pauloensis, which, along with other pollinators, have their populations threatened by various causes, including lack of food diversity due to monoculture. This study evaluated the impact of nutrition on the development of bumblebee colonies. To do this, colonies were started from 52 B. bellicosus queens and 60 B. pauloensis queens using pollen from Eucalyptus grandis (monofloral pollen, M) and pollen from various botanical sources (polyfloral pollen, P) as a substrate for queens to start the nest and then to feed the larvae. Colony development (oviposition, worker birth, time from oviposition to birth, worker weight) was determined until the colony had at least 10 workers. Of the total queens collected in each group, between 48% and 61.5% initiated oviposition, with no differences found between species or treatments. The time elapsed from oviposition to the birth of the first worker was horter in B. pauloensis with monofloral pollen than with polyfloral pollen (24.86 ± 2.44 and 28.29 ± 6.73 days, respectively) (P=0.01). In B. bellicosus, no differences were found (28.29 ± 1.48 monofloral and 29.23 ± 1.53 polyfloral) (P=0.97). The average weight of B. pauloensis workers with monofloral pollen was higher than with polyfloral pollen (0.15 ± 0.05 and 0.12 ± 0.04 g, respectively) (P=0.01). In B. bellicosus, no differences were found (0.13 ± 0.02 and 0.13 ± 0.01) (P=0.32). The results found, although unexpected since bumblebees usually exploit different floral resources simultaneously, show that the botanical origin of pollen can affect colony development and worker size in some bumblebee species.