Low heat tolerance and high desiccation resistance in nocturnal bees and implications for nocturnal pollination under climate change

Authors: GONZALEZ, VICTOR - University Of Kansas; MANWEILER, RACHEL - University Of Kansas; SMITH, ADAM - George Washington University; Oyen, Kennan; CARDONA, DAVID - Us Embassy, Panama; WCISLO, WILLIAM - Us Embassy, Panama

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2023
Publication Date: 12/15/2023
Citation: Gonzalez, V.H., Manweiler, R., Smith, A.R., Oyen, K.J., Cardona, D., Wcislo, W.T. 2023. Low heat tolerance and high desiccation resistance in nocturnal bees and implications for nocturnal pollination under climate change. Scientific Reports. 13, 22320. https://doi.org/10.1038/s41598-023-49815-6.
DOI: https://doi.org/10.1038/s41598-023-49815-6

Interpretive Summary: Megaloptera are major pollinators throughout tropical and temperate ecosystems. Understanding how extreme temperatures may impact these large bees will facilitate stronger predictions about the future distributions and dynamics of these important pollinators. We measured the impact of extreme temperatures on the muscular function of bees that are primarily active throughout the day (diurnal) and night (nocturnal). We also tested how relative humidity impacts temperature tolerance. We found differences in temperature tolerance and dessication resistance among bee populations and that nocturnal bees are more temperature-sensitive than their diurnal counterparts.

Technical Abstract: Predicting insect responses to climate change is essential for preserving ecosystem services and biodiversity. Due to high daytime temperatures and low humidity levels, nocturnal insects are expected to have lower heat and desiccation tolerance compared to diurnal species. We estimated the lower (CT Min ) and upper (CT Max ) thermal limits of Megalopta, a group of neotropical, forest-dwelling bees. We calculated warming tolerance (WT) as a metric to assess vulnerability to global warming and measured survival rates during simulated heatwaves and desiccation stress events. We also assessed the impact of body size and reproductive status (ovary area) on bees’ thermal limits. Megalopta displayed lower CT Min , CT Max , and WTs than diurnal bees (stingless bees, orchid bees, and carpenter bees), but exhibited similar mortality during simulated heatwave and higher desiccation tolerance. CT Min increased with increasing body size across all bees but decreased with increasing body size and ovary area in Megalopta, suggesting a reproductive cost or differences in thermal environments. CT Max did not increase with increasing body size or ovary area. These results indicate a greater sensitivity of Megalopta to temperature than humidity and reinforce the idea that nocturnal insects are thermally constrained, which might threaten pollination services in nocturnal contexts during global warming.