Heat waves increase larval mortality and delay development in the solitary bee Osmia lignaria (Hymenoptera: Megachilidae)

On-Demand

Presenting Author(s)

Grace Genevieve Melone

University of Wisconsin
Madison, Wisconsin

Co-Author(s)

Neal M. Williams

University of California
Davis, California
Clara Stuligross

University of California, Riverside
Riverside, California

In an era of increasing climate uncertainty, understanding the effects of extreme temperature variation on bee biology and ecology is critical to safeguarding their populations. Unlike the hives of social bees, there is no thermal regulation of the nest solitary species. Larvae are protected only by the insulation provided by the nest substrate and thus are more vulnerable to environmental variation. The effects of thermal stress on overwintering adult solitary bees has been well-studied, but we know little about its effects on larval development. We studied the effects of environmental variation in both daily temperature fluctuations and heat waves on the solitary bee, Osmia lignaria, an important orchard pollinator and model organism for solitary bee biology. We used a factorial design to assess heat wave intensity and duration on larval development rate and mortality. Larvae were exposed to heat waves under field realistic diel temperature regimes, 31:20˚ or 37:22˚C for four or seven days at the beginning of development then transferred to ambient (25:15˚C). Temperature strongly affected bee mortality, with the hottest temperature having the highest mortality. Heat wave duration, however, did not significantly affect larval mortality. Compared to the control, bees in the lower temperature heat wave developed faster; whereas bees in the higher temperature showed delayed development. Our study elucidates how a single heat event during larval development can cause high mortality in this vulnerable life stage and impact the entirety of larval development.