Optimization of the bumble bee microcolony test design

Bumble bee microcolonies are queenless, small colonies initiated by a small number of workers that rear haploid male offspring under laboratory conditions. Microcolonies have been a useful tool for research on pesticide effects, nutrition, and development, and recently were evaluated as a toxicity brood test design. The objective of a series of microcolony studies was to optimize this test design by evaluating the impact of pollen quantity and quality, and the size of the workers in the number and weight of emerged male offspring, and consumption of sucrose solution and pollen dough. Our results showed that providing 5 g of pollen, rather than 2 g, during the first 10 days of colony establishment resulted in a higher number of male offspring at the end of the study at day 42. The pollen source also had an impact on the number of male offspring; the pollen composition, as well as carbohydrate and amino acid content were analyzed. Large workers produced similar number of male offspring when compared mixed large and small size workers, however the survival of the worker bees was lower. Small workers produced fewer male offspring than the mixed-size group, but worker survival was similar. Our results suggest that optimal microcolony protocol elements should include the provision of 5 g of pollen dough during the first 10 d of colony establishment, the pollen source of good quality, and workers of mixed size.  The standardization of methodology is critical for pesticide toxicity testing and our work contributes to this effort.