Meeting Abstract
Bumblebees are industrious foragers that routinely carry heavy loads during flight. Man made aircraft consume more fuel per unit time when they are heavily loaded, and aerodynamic theory suggests that this should be the case for flying animals as well. However, we have previously found that the rate of nectar consumption in bumblebees flying over long periods does not decrease as their nectar loads decline, and studies on metabolic rate in bees carrying loads have produced conflicting results. Honeybee studies are complicated by the fact that honeybees alter their flight kinematics for thermoregulatory purposes, and previous bumblebee studies are difficult to interpret because loads were altered by varying nectar consumption, which may have metabolic consequences unrelated to the mechanical demands of weight support. We examined the effects of loading on flight kinematics and metabolic rate in bumblebees (Bombus impatiens) by subjecting individual bees to two loading treatments: one in which bees consumed 20% of their body mass in nectar, and one in which they consumed the same amount of nectar and also had an exogenous load equivalent to another 20% of body mass attached to them. We flew bees in a chamber for 30 minutes, using acoustic analysis to measure flapping frequency, video analysis to calculate stroke amplitude, and flow-through respirometry to measure CO2 production. There was no clear relationship between flapping frequency and flight metabolism, and no significant shift in metabolic rate when bees were carrying an exogenous load. These results suggest that bumblebees are capable of carrying loads during flight without incurring the energetic costs predicted by aerodynamic theory – a result with important implications for the design of micro aerial vehicles and for the economics of foraging in flying insects.
