Climate limitations on the distribution and phenology of a large carpenter bee, Xylocopa virginica (Hymenoptera: Apidae)

We studied climatic correlates of the geographic range of a common large carpenter bee ( Xylocopa virginica (L., 1771)), which reaches farther north than any other Xylocopa in North America. Computational models of the species’ range predicted that summer and winter temperatures limit its northern extent, whereas summer precipitation limits its western extent. We empirically evaluated the climatic constraints imposed by different seasons by examining the winter low-temperature tolerance of X. virginica, and the timing of activity during spring and summer. The bee’s absolute low-temperature tolerance (supercooling point) did not differ between two populations at mid- and high latitudes, and was in excess of requirements of a mean winter minimum temperature. Absolute minimum temperature tolerances may not directly influence the range of X. virginica, whereas other measures of cold tolerance, like exposure duration, might be more relevant. Between years within a study population, spring emergence dates of bees were significantly predicted by spring temperatures and weather (April: 6–11 °C; May: 13–17 °C). Between populations across the bee’s geographic range, bees in warmer climates were observed as much as 2–3 months earlier in the year. This suggests that a major constraint on the bee’s range is the length of the active season, which may be too short for brood development at high latitudes.