Meeting Abstract
Flight can be extremely energetically expensive for many invertebrate ectotherms. Little data on very small flying insects exists to verify how flight metabolic costs change with decreasing body mass. Current estimates are based mostly on measurements from larger insects. We studied the scaling of metabolic rate (FMR) among 13 species of stingless bees, ranging from 1-115mg in body mass, using flow-through respirometry at a fixed temperature of 25°C. We found that an FMR scaling exponent of 2.2, indicating that smaller bee species expend less energy in flight than expected for their size. We measured wing area and veination, head, thorax, and abdomen mass, load carrying, and wing beat frequency (WBF) to explain our results. We found that WBF did not scale with body mass. Load carrying scaled isometrically. Smaller stingless bee species had relatively larger heads. Smaller species had relatively larger wings with less veination. When compared to FMR for all flying insects, we found a breakpoint in the scaling relationship at 53mg body mass. Below this, FMR scaled with and exponent of 1.2 while it scaled with an exponent of 0.67 above, suggesting that smaller flying insects have mechanisms which decrease the costs of flight. We determined that flight temperature did not contribute to FMR by measuring Q10 for each species between 25-35°C. Q10 was approximately 1 over this range. Thermal performance curves varied by species; flight metabolic rate increased or decreased with increasing air temperatures in some species. In others, there was no effect of air temperature between 25-40°C. However, smaller species had lower flight CTmax than larger species, and therefore may be less tolerant of rising air temperatures.
