Effects of temperature and wildflower strips on survival and nutrition dynamics of Megachile rotundata under extended cold storage

Authors: PARK, MIA - North Dakota State University; DELPHIA, CASEY - Montana State University; Prince, Cassandra; Yocum, George; Rinehart, Joseph - Joe; O'NEILL, KEVIN - Montana State University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2022
Publication Date: 8/14/2022
Citation: Park, M.G., Delphia, C.M., Prince, C.M., Yocum, G.D., Rinehart, J.P., O'Neill, K.M. 2022. Effects of temperature and wildflower strips on survival and nutrition dynamics of Megachile rotundata under extended cold storage. Environmental Entomology. https://doi.org/10.1093/ee/nvac062.
DOI: https://doi.org/10.1093/ee/nvac062

Interpretive Summary: The annual alfalfa hay crop is valuated at about $8.8 billion and is an essential input for the dairy and livestock industries. The production of alfalfa seed in North America is primarily dependent upon the pollination services provided by the alfalfa leafcutting bee (ALCB), and developing management practices that ensure the availability of high-quality bees of this species is a key component for the long-term sustainability of alfalfa hay production. One understudied factor that could affect bee quality is the nutrition that they receive prior to overwintering. With our hypothesis being that more diverse nutritional sources would increase overwintering survival, we released ALCB in alfalfa plots with and without supplementary wildflower strips and assessed the resulting progeny. Counter to our expectations, the floral treatment had no effect on mass or overwintering survival, which means that bees did just as well in the plots with wildflowers as they did in plots without. Our research provides guidance for the inputs required for maintaining a healthy population of this critically important pollinating species.

Technical Abstract: Enhancing landscapes with wildflowers is a primary conservation strategy to address a dearth of floral resources for bee pollinators. Previous work demonstrating benefits of habitat enhancements is largely focused on social bees even though most bees are solitary. Solitary bees spend much of their lifecycle in a dormant stage of overwintering. We tested whether supplementing alfalfa fields with wildflower strips improves M. rotundata overwintering success in long term cold storage. Megachile rotundata is an economically important pollinator of alfalfa in the United States; however, populations are unsustainable. While the commercial standard is to overwinter M. rotundata at a static 6°C thermal regime (STR), previous work in our lab has shown increased overwintering survival under a fluctuating thermal regime (FTR), where cells are exposed to a daily warm pulse of 20°C for one hour. In summer 2017, M. rotundata adults were released in 6 research alfalfa plots, half with adjacent wildflower strips. Completed nests were marked weekly, harvested in September, and stored in STR. After a year, cells were randomly assigned to remain in STR for 6 months or in FTR for a year; emergence rates were observed monthly. Macronutrient levels of newly emerged females were assessed at 0, 2 and 4 months after temperature treatments began. FTR improved M. rotundata winter survival under long-term cold storage. No measurable effect of wildflower strips on M. rotundata overwintering success or nutrient stores was observed, most likely due to low visitation. Timing of nest establishment emerged as a key factor: offspring produced late in the season had lower winter survival and dry body mass. Sugars, glycogen and trehalose stores increased under FTR but not STR. Total lipid stores were depleted faster under FTR. Wildflower strips did not provide measurable benefits to M. rotundata; however, our investigation into nutrition dynamics during cold treatments extends our physiological understanding of the benefits, and potential costs, of FTR.