To study how climate change affects mason bees, CaraDonna’s team set up three types of nesting environments in Arizona’s Santa Catalina Mountains (above), where the bees thrive. The team manipulated the temperatures of the nests by painting them to simulate past, present and future climates. The team painted a third of the nests black to absorb more radiant heat, thus simulating a future climate predicted for the years 2040 to 2099. By painting another third with a white, reflective, cooling treatment, the team sent that third of the nests back in time to a climate similar to that of the 1950s. As a control, the team painted the final nests with a transparent paint, leaving their natural wood color. The experiment included 90 nests total, each housing anywhere from 2 to 15 bees.

CaraDonna ran the experiment twice during two back-to-back seasons. Bees experienced the altered environments from early in larval development all the way through metamorphosis and adult diapause, which is a term to describe insect hibernation. CaraDonna noted that the bees in nests simulating past and current climates woke up from diapause and emerged in February, which is normal.

The bees nesting in the warmer boxes, however, underwent multiple disturbing changes. Not only were their mortality rates remarkably high, they also emerged from diapause over a much longer period of time. While mason bees in this area typically emerge from diapause over the course of 10 to 15 days, bees in the warming treatment emerged over the course of 50 days.

“This suggests that they are responding to a stressful environment,” CaraDonna said. “Because their emergence times are altered, they now potentially have fewer floral resources available to them as a population, and it might be a lot harder to find mates.”