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

Authors: DEGRANDI-HOFFMAN, GLORIA - Retired ARS Employee; GRAHAM, H. - Retired ARS Employee; Corby-Harris, Vanessa; Chambers, Mona; WATKINS-DEJONG, EMILY - Retired ARS Employee; Ihle, Kate; Bilodeau, Anita

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 3/4/2025
Citation: Degrandi-Hoffman, G., Graham, H., Corby-Harris, V.L., Chambers, M.L., Watkins-Dejong, E., 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);266. https://doi.org/10.3390/insects16030266.
DOI: https://doi.org/10.3390/insects16030266

Interpretive Summary: Management practices for honey bee colonies that mitigate the effects of climate change on fall weather patterns are needed to reduce overwintering losses and securing adequate numbers of hives for pollination. Warmer fall temperatures are extending the period when honey bees can forage and Varroa mites can migrate among colonies. A solution is to put colonies in cold storage facilities in the fall for overwintering. How well various lines of honey bees tolerate cold storage is unknown. We overwintered Varroa resistant Russian bees in cold storage facilities and compared colony size and survival and the percentage that could be rented for almond pollination and were alive after almond bloom with colonies of Italian bees not selected for mite resistance. We also compared overwintering management costs and colony size and survival between cold storage and overwintering Russian bees in apiaries in the southern USA. We found that Russian colonies had comparable survival to Italian colonies when overwintered in cold storage and similar percentages that could be rented for almond pollination. Colony sizes after cold storage and almond bloom did not differ between Russians and Italian bees. Though Russian colonies were smaller than the Italian when hives went into cold storage, the colony sizes were similar when they were removed suggesting greater longevity of Russian bees while in cold storage. Costs were lower for overwintering Russian colonies in cold storage compared with outdoor apiaries. The percentage of colonies that survived and could be rented for almond pollination were comparable between the two management methods, but after almond bloom significantly more colonies overwintered in cold storage were alive compared with those overwintering in apiaries. The results indicate that the combination of Varroa resistant Russian bees to keep Varroa mite populations low and overwintering in cold storage can be a viable management strategy for mitigating the effects of climate change on overwintering colony survival.

Technical Abstract: To secure adequate numbers of hives for pollination, strategies are needed for honey bee colony management that mitigate the effects of climate change and reduce overwintering losses. Climate change is causing warmer temperatures later in the fall and extending periods when flight activity and Varroa mite migration among honey bee hives can occur. Here we report on a management plan using Varroa resistant Russian bees overwintered in indoor cold storage facilities. We compare the survival and growth of Russian colonies with unselected Italian bees. We also compare overwintering management costs and colony size and survival between cold storage and overwintering Russian hives in apiaries in the southern USA. We found that Russian colonies had comparable survival to unselected European lines when overwintered in cold storage and similar percentages that could be rented for almond pollination. Russian and unselected colonies had equivalent populations in September, but by October when colonies were put into cold storage, Russian colonies were smaller. After cold storage, Russian and unselected colonies were similar in size indicating that Russian bees might have greater longevity while in cluster than unselected lines. Costs were lower for overwintering Russian colonies in cold storage compared with outdoor apiaries. The percentage of colonies that survived and could be rented for almond pollination were comparable between the two management methods, but after almond bloom significantly more colonies overwintered in cold storage were alive compared with those overwintering in apiaries. The results indicate that the combination of Varroa resistant Russian bees and overwintering in cold storage can be a viable management strategy for mitigating the effects of climate change on overwintering colony survival.