Cold storage as part of a Varroa management strategy: Effects on honey bee colony performance, mite levels and stress biomarkers

Authors: Meikle, William; Corby-Harris, Vanessa; Ricigliano, Vincent; Snyder, Lucy; Weiss, Milagra

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2023
Publication Date: 7/22/2023
Citation: Meikle, W.G., Corby-Harris, V.L., Ricigliano, V.A., Snyder, L.A., Weiss, M. 2023. Cold storage as part of a Varroa management strategy: Effects on honey bee colony performance, mite levels and stress biomarkers. Scientific Reports. 13. Article 11842. https://doi.org/10.1038/s41598-023-39095-5.
DOI: https://doi.org/10.1038/s41598-023-39095-5

Interpretive Summary: Varroa mites, a serious pest of honey bees, reproduces on immature bees (larvae and pupae). This, one way to control Varroa mites might be to cause the bee colony to stop producing immature bees, wait until all of the immature bees have matured into adults, and then treat the colony with a mite pesticide to kill the remaining adult mites. In this study we put the bee colonies into a cold storage shed, with low temperatures and no light, to cause them to stop producing any more brood and then treated them for mites. We monitored hive weight and temperature, and sampled bees to determine mite levels and bee health (measuring gene expression and physiological stress). The method worked to stop brood production, but in the final sample 4 months after treatment, mite levels were not lower in the full treatment group. Most of the differences in the experiment were due to which year the experiment was run (we ran 2 experiments) rather than cold storage. In fact, cold storage did not seem to have much effect on bee stress. While the treatment (cold storage + miticide) did not work, we think that if we change when and how long colonies are put in cold storage, and make sure they do not have high mite levels before storage, the treatment may have potential.

Technical Abstract: Placing honey bee colonies in cold storage has been proposed as a way to induce a pause in brood production as part of a Varroa mite treatment plan. Here, we exposed colonies to combinations of with or without a late summer-early fall cold storage period and with or without a subsequent miticide application, and then measured the effects of those treatments on colony-level variables (i.e. colony size, Varroa density, and hive temperature) and pooled individual-level variables that are associated with nutritional and stress responses. Colonies were assessed before and after cold storage, and post winter, and the experiment was conducted twice. The cold storage plus miticide treatment strategy did not have a major impact on colony health. Cold storage did induce a brood pause: little brood was present after cold storage, and hive temperature data indicated that most or all brood had emerged after about two weeks. However, Varroa levels in February after treatments were not significantly affected by treatment, and we found comparatively few effects on either the colony or individual level because of the cold storage or miticide application. The two experiments were very different: rainfall, and bee forage availability, were much higher the second year, and colonies were over 2.5 times larger on average the second year compared to the first, both in terms of adult bee mass and brood area. Expression levels of nutrition and stress response genes were also significantly higher the second year. Colony survivorship from September to February was 42% the first year and 60% the second year. The results indicate that limited cold storage itself would likely have little impact on most colony- and individual measures of health, but for such a strategy to succeed levels of stressors, such as Varroa, may also need to be low.