Effect of nest microclimate temperatures on metabolic rates of small carpenter bees, Ceratina calcarata (Hymenoptera: Apidae)

Small carpenter bees (Ceratina calcarata Robertson) (Hymenoptera: Apidae) build their nests in both sunny and shady sites, so maternal decisions about nest sites influence the thermal environment experienced by juveniles throughout development. A previous study demonstrated that when larvae and pupae were raised in the laboratory at room temperature, those from sunny nests developed more slowly than those from shady nests. This suggested that bees developing in sunny nests slowed their metabolism or that bees developing in shady nests increased their metabolism. To test this hypothesis, we performed a field experiment in which bees nested in full sun, full shade, or semi-shade. We brought larvae and pupae into the laboratory to be raised to adulthood at room temperature and measured their metabolic rates (VCO2) at 10 °C, 25 °C, and 40 °C. As expected, bees had higher VCO2 at higher test temperatures, but significant interaction also occurred between test temperature and field treatment, such that bees from sunny nests exhibited higher metabolic rates at 40 °C. Because small carpenter bees frequently nest in full sun, adaptation to high nest temperatures may involve activation of thermal protection mechanisms at the cost of slower development.