Meeting Abstract
Bumblebees forage widely for floral resources, often carrying immense loads of pollen or nectar over long distances. Their endogenous fuel reserves are minimal, so bees burn a portion of the nectar they have collected to fuel their return journey to the hive. Despite the critical role that resource collection plays in hive growth and fitness, little data exists on the fuel efficiency of bumblebees carrying loads, or on the limits of their flight endurance. We expected that bees would use more fuel per unit time while carrying heavier loads of nectar, and that their fuel efficiency would improve as nectar load diminishes, resulting in an exponential decline in total body mass. To test this prediction, we starved bumblebees (Bombus impatiens) for several hours and then allowed them to sate themselves with 1 g/ml sugar solution. We developed an apparatus in which bees must hover constantly, and flew bees until exhaustion, weighing them every 10 minutes. Surprisingly, total body mass did not decline exponentially, but rather linearly, suggesting that bumblebee flight metabolism is less sensitive to the addition of extra loads than predicted. Bees typically consumed 50-65% of their body mass in nectar and were able to fly for 2-3 hours, burning approximately 2-4 mg of nectar per minute. The underlying causes of individual variability and potential effects of environmental factors on fuel efficiency warrant further investigation, as these could have important consequences for hive growth and survival.
