Size, sex, & survival: Water balance across temperatures in the alfalfa leafcutting bee

Authors: JOHNSON, MEREDITH - North Dakota State University; WAYLETT, CHRISTOPHER - North Dakota State University; SOKALSKI, LUKAS - North Dakota State University; Rinehart, Joseph; BOWSHER, JULIA - North Dakota State University; GREENLEE, KENDRA - North Dakota State University

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2026
Publication Date: 2/18/2026
Citation: Johnson, M.G., Waylett, C., Sokalski, L., Rinehart, J.P., Bowsher, J., Greenlee, K. 2026. Size, sex, & survival: water balance across temperatures in the alfalfa leafcutting bee. Journal of Insect Physiology. https://doi.org/10.1016/j.jinsphys.2026.104958.
DOI: https://doi.org/10.1016/j.jinsphys.2026.104958

Interpretive Summary: Alfalfa is a vital crop produced in the United States, especially as livestock feed. The alfalfa leafcutting bee is a key pollinator that drastically increases alfalfa seed set. These bees are managed across the country in differing climates, from cool northern states to hotter, drier regions. However, little is known about how heat and water stress affect adult male and female bees differently, and how this might influence their survival. In this study, we discovered that male bees are more likely than females to dry out and die in hot, dry conditions. Females, which are larger and thus carry more water in their bodies, were found to survive longer. Both males and females lose water more quickly as temperatures rise, but males lose water at a higher rate through both their body surfaces and through respiration. These findings explain why males are may be more vulnerable to heat and drought. This research will help farmers and bee managers understand how field temperatures and water stress affect alfalfa leaf cutter bee survival. Our findings can guide strategies to protect managed bee populations, for example, timing bee releases to avoid extreme heat. Through maintaining a healthy bee population, farmers can ensure reliable alfalfa pollination and seed production, which in turn supports livestock alfalfa feed production. Our study additionally advances scientific knowledge of how small, flying bees cope with water stress, and provides critical insights that will help predict pollinator health under abiotic anomalies.

Technical Abstract: Water balance is critical to insect survival. Megachile rotundata, a solitary bee, is used for alfalfa pollination across the United States, necessitating performance across a range of environmental conditions. We investigated sex-specific effects of temperature on desiccation tolerance, cuticular permeability, and water loss rates in adult M. rotundata. Females were larger than males in both wet mass (42.9 ± 8.2 mg vs. 32.5 ± 6.9 mg) and body water content (27.9 ± 7.1 mg vs. 20.8 ± 5.2 mg), with body water content scaling hypermetrically with dry mass while male body water content scaled hypometrically. For all bees, survival time decreased with increasing temperature and was positively associated with body water content, with the effect strongest at lower temperatures. Cuticular permeability was 1.8-fold higher in males than females. For both sexes, mass-specific water loss rates increased with temperature, but 1.6-fold greater in males. Comparisons of water loss routes revealed that respiratory water loss substantially exceeded cuticular water loss in live bees, and the relative contribution of respiration increased with temperature. Overall, these results indicate that sex, body size, and route of water loss interact to determine desiccation risk in M. rotundata, and that males may be more vulnerable to desiccation at high temperatures due to higher cuticular permeability and respiratory water loss rates. These findings provide insight into the physiological adaptations of M. rotundata to water stress and contribute to a broader understanding of insect water balance mechanisms.