Adapting overwintering honey bee (Apis mellifera L.) colony management in response to warmer fall temperatures

Authors: HOFFMAN, GLORIA - RETIRED ARS EMPLOYEE; GRAHAM, HENRY - RETIRED ARS EMPLOYEE; COPELAND, DUAN; CHAMBERS, MONA; WEISS, MILAGRA; Ihle, Kate; BILODEAU, ANITA

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 3/4/2025
Citation: Hoffman, G., Graham, H., Copeland, D.C., Chambers, M.L., Weiss, M., Ihle, K.E., Bilodeau, A.L. 2025. Adapting overwintering honey bee (Apis mellifera L.) colony management in response to warmer fall temperatures associated with climate change. Insects. 16(3). Article 266. https://doi.org/10.3390/insects16030266.
DOI: https://doi.org/10.3390/insects16030266

Interpretive Summary: Warmer fall temperatures can lead to overwintering losses of honey bee colonies and cause honey bees to fly and parasitic Varroa mites to immigrate into colonies later in the fall. A management strategy that might reduce colony losses is the combination of Varroa-resistant Russian honey bees and overwintering colonies in indoor cold storage facilities. Using this strategy, we found that Russian bees overwintered in cold storage have similar survival, colony sizes, and percentages that could be rented for almond pollination to unselected European colonies. An analysis of fat body metrics, which are key to overwintering survival, showed similar trends between Russian and unselected bees. A cost comparison of overwintering Russian bees in cold storage versus apiaries showed that overwintering in cold storage costs less than in apiaries. The percentages of colonies that survived and were rented for almond pollination were similar between overwintering in cold storage or apiaries. The combination of Varroa-resistant Russian bees and cold storage overwintering can be a viable management strategy for mitigating the effects of climate change on colony survival.

Technical Abstract: Management strategies are needed that mitigate the effects of warmer fall temparatures on honey bee colony losses. Extended periods of warmer fall temperatures prolong periods of honey bee flight and parasitic Varroa mite immigration into colonies. We report on a management strategy using Varroa-resistant Russian honey bees overwintered in indoor cold storage facilities, and compare colony survival and growth with that of unselected European bees. Fat body metrics that are key to overwintering survival were also measured in Russian and unselected bees. Comparisons between overwintering Russian colonies in cold storage versus apiaries were also conducted. Russian and unselected colonies overwintered in cold storage had comparable overwintering survival and percentages rented for almond pollination. However, more Russian colonies overwintered in cold storage were alive after almond bloom than those overwintered in apiaries. Fat bodies in Russian and unselected bees gained weight while in cold storage. Protein concentrations increased and lipids decreased. Changes in lipid concentrations were inversely related to the number of brood bees reared while in cold storage. Similar percentages of colonies overwintered in cold storage or outdoor apiaries survived and were rented for almond pollination. An economic analysis indicated that overwintering Russian colonies in cold storage costs less than in apiaries. Our study indicates that cold storage can be a viable management strategy for mitigating the effects of climate change on colony survival.