Microclimate and season affect flight initiation in the alfalfa leafcutting bee

Authors: EARLS, KAYLA - Washington State University; Rinehart, Joseph; GREENLEE, KENDRA - North Dakota State University

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2025
Publication Date: 3/8/2025
Citation: Earls, K., Rinehart, J.P., Greenlee, K. 2025. Microclimate and season affect flight initiation in the alfalfa leafcutting bee. Ecological Entomology. https://doi.org/10.1111/een.13432.
DOI: https://doi.org/10.1111/een.13432

Interpretive Summary: The alfalfa leafcutting bee is heavily managed cavity nesting bee that is widely used for pollinating alfalfa for seed production. Although this bee has been used to pollinate crops other than alfalfa, these uses of the bee have been limited by a number of factors. For instance, the fact that they are unlikely to fly in cool air temperatures makes them unreliable for pollination of the low bush blueberry, an important crop in northeast North America. In this study, we conducted two different experiments to assess how temperature affects flight. In the first, we built a microclimatic weather station that recorded key variables at the surface of their nests while a camera recorded the time of the first flight of the morning. In the second, we built a nest that would warm their cavities well above the air temperature. Our results indicate that air temperature at the surface of the nest and the amount of solar radiation received both significantly affected the timing of the first flight. Furthermore, when the nesting cavities were heated, bees started to fly significantly earlier than unheated controls. These results demonstrate the importance of nest temperature on flight in this species, and identifies parameters that may be altered to increase their effectiveness in cooler climates.

Technical Abstract: Weather conditions are often reported for a large area, but small-bodied organisms experience abiotic conditions on a finer scale. For insects that nest in cavities, the temperatures in and around the cavity may be important for flight initiation. Cavities can expose nesting bees to conditions that differ from broad weather readings and may affect when or if bees fly. The purpose of this study is to determine which environmental factors influence flight in early and late summer and how altering internal cavity temperatures contributes to flight initiation in a cavity nesting bee, Megachile rotundata. Two nest boxes were created to monitor flight initiation. The first nest box had no manipulations and recorded several abiotic environmental conditions, including multiple temperatures, light, wind speed, and humidity. The second nest box had one side heated and the other unmanipulated. First flight for individual bees was recorded and measured from 7-11 am daily. A hierarchical cluster analysis showed that early or late summer was an important factor for flight initiation. All environmental variables at the time of first flight were significantly different between early and late season except for air pressure. Early in the season, temperatures inside and at the face of the box were higher than ambient readings. Heating the nest cavities promoted flight at lower ambient temperatures and at earlier times. Understanding how abiotic condition affect flight initiation will help model flight behavior in response to climate change and allow farmers to provide optimal flight conditions when weather is unfavorable.