The effect of soil moisture on the emergence and survival of a solitary sand-nesting bee, Megachile wheeleri

Globally, one of the most prominent biological responses to climate change is a shift in phenology. This is a particular concern for organisms that provide essential ecosystem services, such as wild bees. The most diverse group of bees are solitary, ground-nesting bees, however, a lack of basic biological information about these bees makes it difficult to predict how they will respond to a changing climate. Temperature is an important climatic cue for bee emergence, but soil temperature is modulated by various factors, including moisture. Precipitation patterns are expected to shift under climate change, thus, it is crucial to understand how moisture affects ground-nesting bee biology. Here, we investigate the effect of soil moisture on the emergence of a sand-nesting leaf-cutter bee, Megachile wheeleri, in a coastal dune ecosystem. We hypothesized that drier conditions would result in earlier emergence, because of less evaporative cooling. To test the effect of soil moisture on M. wheeleri emergence, we excavated nests and reburied them in experimental tubs. Half of the tubs were randomly assigned a water-exclusion treatment and were covered with a fiberglass roof that decreased soil moisture content by 0.12 wfv and increased soil temperature by 0.6^ºC. Differences in soil moisture content did not affect emergence date (Chi = 0.001, p = 0.97) or survival (Chi = 2.08 p = 0.15). Our results indicate that M. wheeleri emergence timing and survival will likely not be affected by altered precipitation patterns predicted for this area under climate change.