Assessing the effects of cold storage regimes of North American Bombus gynes

Authors: Lindsay, Tien; Hagen, Marcia; KAPHEIM, KAREN - Utah State University; Knoblett, Joyce; Rinehart, Joe; STRANGE, JAMES - The Ohio State University

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2024
Publication Date: 5/3/2024
Citation: Lindsay, T.T., Hagen, M.M., Kapheim, K., Knoblett, J.N., Rinehart, J.P., Strange, J. 2024. Assessing the effects of cold storage regimes of North American Bombus gynes. Journal of Applied Entomology. https://doi.org/10.1111/jen.13261.
DOI: https://doi.org/10.1111/jen.13261

Interpretive Summary: Since the 19th century, humans have seen the value of Bombus pollinating services and the potential to harness it as a commodity. While much progress has been made to understand and manage the bumble bee life cycle for domestication, the natural overwintering phase in North American Bombus species, which all overwinter as mated queens, has yet to be fully understood or readily used in captive settings including storing bees for later use. This study provides new insights to exploring nontraditional overwintering methods and has important implications for Bombus physiology, longevity, and management. We compared traditional cold storage techniques using constant temperatures to one with a daily pulse of warm temperature, a practice known as fluctuating thermal regime (FTR). This was done for three North American Bombus species: the common eastern bumblebee, Hunt’s bumblebee, and the yellow-faced bumblebee. When using FTR, survival of Hunt’s bumblebee, and yellow-faced bumblebee queens was significantly lower than those stored using traditional cold storage, while the common eastern bumblebee showed significantly higher survival when using FTR. Moreover, individual queen characteristics, climatic origins, and colony age all influenced duration in cold storage. Our results demonstrate extended captive Bombus cold storage is a multi-faceted challenge and our study provides insight into how outside thermal regimes and other physiological factors can interact and influence overwintering survival. Our findings have economic applications for improving bee rearing, and should be valuable to institutions involved with aiding Bombus populations.

Technical Abstract: Bumble bees are the primary commercial pollinators for greenhouse grown crops and managing them requires insight into the Bombus life cycle. However, some aspects of the life cycle are poorly understood. An obstacle to maximizing profitability of commercial bumble bee rearing is mimicking the natural overwintering period. While mated, adult Bombus gynes can be stored for a short term at a constant low temperature. However, survival rates are low during cold storage, particularly when storage periods exceed a month. To address this, we compared constant temperature cold storage to a cold regime regime with a daily pulse of warm temperature, known as fluctuating thermal regime (FTR). We tested the effects of FTR on gyne survival and quantified post-cold storage lipid content in three species used for commercial pollination in North America: B. vosnesenskii, B. huntii, and B. impatiens. We tested the hypothesis that Bombus gynes stored in FTR have increased survival compared to gynes stored in constant low temperature (CLT) regime. We further assessed how factors outside of storage temperature may influence cold storage survival, including weight, size, and colony age. We found that survival responses varied among species. Bombus vosnesenskii and B. huntii had a lower survival rate in FTR compared to CLT; however, this was in contrast to B. impatiens gynes, which had a higher survival rate in FTR. We did not observe significant effects of FTR on lipid stores for any species, but survival increased with increasing initial weight prior to cold storage. Moreover, survival decreased as colony reproductive age increased, likely because early emerging gynes were heavier than later emerging gynes. Our study provides insight into how cold storage conditions interact with colony and gyne characteristics to influence captive overwintering survival. Our findings have economic applications for improving bee rearing, and should be valuable to institutions involved in aiding wild declining Bombus populations.