Foraging Economics of the Hunt Bumble Bee, a Viable Pollinator for Commercial Agriculture

Globally, there are only five bumble bee (Hymenoptera: Apidae, Bombus) species that have been successfully commercialized for agriculture. The Hunt bumble bee, Bombus huntii Green, 1860, has been recognized as a suitable pollinator of crops and has a broad distribution in western North America, making it a viable candidate for commercialization. In this study, our goal was to characterize the foraging dynamics of B. huntii female workers under open field conditions. To accomplish this goal, we monitored three B. huntii colonies over an 8-wk period in the summer of 2012 in northern Utah. Using marked bees, we studied the relationship between foraging duration/offloading and pollen/nonvisible pollen collection. In total, we observed 921 foraging events across all three colonies. Of our observations, 82% (n = 756) were foraging events that included both a departure and arrival time observation. Average duration of pollen and nonpollen (i.e., nectar) trips across foragers is 41.86 +/- 5.65 min (+/- SE) and 32.18 +/- 5.89 min, respectively. Workers spent a significantly longer time offloading pollen in the nest after a foraging trip relative to workers without pollen present on their corbicula. Pollen foraging rate increases over the course of the day, likely due to the time it takes to learn how to forage on a diverse array of flower morphologies. Our study provides data on how long it takes for B. huntii to forage in open field conditions and will be useful when comparing foraging rates in controlled crop systems.