Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Effects of color and corresponding UV wavelengths on the nesting preferences of Megachile rotundata

The Alfalfa Leafcutting Bee (Megachile rotundata) is a solitary cavity nesting bee that is commercially managed for alfalfa production. Farmers use commercial nesting blocks that are manufactured with pre-set colors and patterns believed to help bees locate their nests. This study investigates how color and corresponding ultraviolet (UV) light wavelengths affect nesting preferences of Megachile rotundata. While previous research has explored visual cues and spatial memory in solitary bees, the influence of UV wavelengths on nest selection remains underexplored. Though studies are limited, honeybees (Apis mellifera) can serve as a model, possessing trichromatic vision sensitive to UV (350 nm), blue (440 nm), and green (530 nm) wavelengths. Environmental factors, including microclimate, shape nesting behavior. Lighter-colored nests reflect more UV, maintaining cooler temperatures and enhancing suitability; whereas darker nests absorb UV, raising cavity temperatures and deterring females. With this in mind, nest blocks in this study were split evenly into four quadrants that were painted red, white, purple, and unpainted. We assessed UV reflection/absorption, color wavelength, nest temperature, brood parameters, nest completion, weather, leaf cap length, and diapause status. We found that bees exhibited a higher preference for red quadrants over purple and white. This challenges our understanding of solitary bee preference, and by optimizing UV and color cues in nesting blocks, it may be possible to improve nesting efficiency, reproductive success, and pollination outcomes in agricultural ecosystems.