Meeting Abstract
Native bees are increasingly under threat from a wide variety of anthropogenic forces, including rising temperature. Warmer temperatures are already affecting organisms indirectly, through behavioral or range modification, or through adaptive plasticity as in advanced production of heat shock proteins. However, as temperatures approach organisms’ critical thermal maxima (CTmax), they are more likely to directly impact survival, and understanding thermal tolerances will increase in importance. CTmax is most often measured in adult insects by observing knockdown while ramping temperature. However, in some cases it is the larval stages that are most vulnerable to thermal extremes, and bee larvae cannot easily be visually assessed for knockdown. Thermolimit respirometry solves this problem by measuring volume of CO2 in air that passes over an acclimated larva in an enclosed chamber. This allows for respiration to be monitored, and pinpoints time or temperature of death. Xylocopa californica, the desert carpenter bee, nests above ground, leaving its larvae particularly exposed to the effects of temperature. In the Sonoran Desert of southern Arizona, carpenter bees are near the southernmost and hottest part of their range, and possibly near the edge of their thermal geographic range. To assess thermal tolerance of during development, I used thermolimit respirometry on all larval and pupal stages. The least thermally tolerant life stage died at 52.6 degrees C. Record high local temperatures in southern Arizona have reached 47 degrees C. Measurements of developmental thermal tolerances at each life stage suggest that this critical pollinator is close to the maximum it can physiologically tolerate in a warming world.
