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Winter Losses
By: Ross Conrad
Winter colony losses: I regularly come across statements that claim the most serious problem beekeepers face is the Varroa mite. With about a dozen approved acaricides available to U.S. beekeepers, there is no good reason why the majority of annual colony losses our industry is experiencing should be caused by Varroa.
This is the time of year when beekeepers are scrambling to finish preparing their colonies for Winter. Supplemental feeding, mite and pest control, inspecting for disease, confirming the presence of a healthy fertile queen, along with installing mouse guards, wrapping and insulating, and securing outer covers are all part of the annual routine. A huge percentage of northern bees are transported down south where the temperatures are easier on the bees, and beekeepers can continue to work the hives, breed queens, treat for diseases and mites, and potentially even harvest some honey as well. Other beekeepers build special climate-controlled buildings to overwinter their colonies in.
And yet, despite all this effort, large numbers of hives die during Winter. Sometimes the hives die because we miscalculate their food requirements, fail to treat for mites effectively, or simply because the queen got old and failed at a time when the colony is unable to raise a newly mated queen to replace her. All too often however, our bees are dying for reasons unrelated to what we do or don’t do.
This may sound like I am shooting from the hip, but I am basing this last statement on first-hand experience. This past Winter was a perfect example. My 2024-2025 Winter losses were what I would consider high: approximately 30 percent. But what is troubling me more than the level of loss, was that it wasn’t consistent. I had a couple apiaries that had losses over 55 percent with one of them experiencing 100 percent loss. I also had a couple apiaries that had losses under ten percent with one of them experiencing 100 percent survival. Given that I basically treat all my hives the same, the dramatic range of losses among my bee yards suggests that the primary cause of my colony losses is not something that I am doing, or failing to do. This is concerning because it suggests that my ability to prevent future hive deaths is limited.
If my colony losses were due to a failure on my part, I would expect to see a more consistent level of die-off among all my bee yards. The fact that this is not happening indicates to me that what is killing off most of my hives is something that is originating from outside my apiaries, not from within them. Sure, it is theoretically possible that the yards with high Winter losses were hit by a disease that only spread in those specific corners of my county, or from pests that were extremely localized in their impact. But it is much more likely that my colony deaths are a result of known and proven phenomenon. The two leading candidates are climate destabilization and pesticide exposure.
We have to remember that the high level of colony losses being experienced by beekeepers throughout most of the world is not happening in isolation. Dramatic insect population declines in general are being documented globally from Germany (Hallmann et. al., 2017) to Puerto Rico (Lister and Garcia, 2018). More recently in Costa Rica the collapse of insect populations deep in the rainforests of the island nation has been documented by insect monitor Dan Janzen who came up with a simple, yet startlingly effective approach to monitoring the local insect populations. Janzen hung up a bed sheet and placed lights next to it at night to attract nocturnal insects (Janzen and Hallwachs, 2021). When first tried in 1978, thousands of moths were attracted to the bed sheet, many of the species scientifically identified for the very first time. By 2019 an identical light trap erected in the exact same place and at the same time of year provided a graphic illustration of the world-wide level of insect loss.
The lack of pesticide use and industrial agricultural activity in many of the areas where insect population collapses have been documented, suggests that the climate crisis is a, if not the, primary driver of global insect decline. Many of the problems created by our rapidly destabilized climate from a lack of nutritional resources caused by drought or shifting bloom times, to novel pest and diseases can be, can be addressed by diligent beekeepers caring for their colonies. While it may play a role in some instances, it is unlikely that the climate disaster is playing a significant role in the majority of honey bee colony deaths, simply because beekeepers can act as a buffer and protect colonies from the worst impacts of the climate crisis.
Honey bees are however, regularly exposed to chemical pesticides. Remember that by far, the greatest percentage of hives in the United States are managed by a relatively small number of commercial migratory beekeepers who derive the largest portion of their income from farm pollination services. Between the regular movements of hives in and out of large chemically-based agricultural operations, to the spraying of crops located near stationary apiaries, managed honey bee colonies are probably exposed to more toxic pesticide residues of various kinds and in greater numbers than any other insect species on earth.
Once again, my own experience supports these concerns. When I look back over my records for the past 5 years, my beeyard that consistently has the lowest Winter losses happens to be the apiary that is farthest from chemically cultivated row crops like genetically modified corn and soybeans. Coincidence? Perhaps. I plan on testing this hypothesis by supporting the work of researchers gathering data on pesticide residues in bee pollen and correlating the findings with the distance of apiaries to row crops.
The danger modern agriculture poses to honey bees is disturbing because the pollination bees provide is considered a huge benefit to agriculture in general. Conversely, agricultural activity that often-includes flowering crops that benefit from insect pollination, has historically been a huge benefit to pollinators like honey bees. In the late 1800s and early 1900s, before highly toxic pesticide use became so ubiquitous, beekeepers in places like Vermont could keep a hundred colonies in a single yard and reliably count on harvesting an average of one hundred pounds of honey from each hive. One hundred colony beeyards yielding one-hundred-pound averages in New England has long become a thing of the past (Mares & Conrad, 2020).
Today science is documenting how industrial chemical-based agriculture is detrimentally influencing bee populations. For example, bees are found to do best in locations where organic agriculture is practiced in or near areas that also include natural uncultivated habitats that feature long-lasting perennial plants such as meadows. Research published in the Journal of Applied Ecology indicates that the combination of organic (low-chemical reliance) farms and natural ‘wild’ areas support significantly more wild bees than either habitat on its own (Czechofsky et al. 2025).
In recent decades beekeepers across America have been complaining of honey bee queens that do not live as long as they used to. I would hear these reports and I must admit I was somewhat skeptical. Given the propensity for honey bees to readily swarm when given the opportunity, I figured many of the reports of premature queen failure were false claims being made by inexperienced beekeepers whose hives simply swarmed and failed to successfully replace their queen. Recent observations however, have forced me to reevaluate this perspective.
The last two Springs have featured weather that was much milder than normal allowing me to get out and inspect and reverse my bees in the first half of April, about two-weeks earlier than usual. Two years ago while reversing hives on the 12th of April, I noticed numerous colonies that were queenless. Some were drone layers, but some had lots of bees and capped brood, but no eggs, or uncapped larvae. Meanwhile other colonies simply had plenty of bees but no brood of any kind.
Normally when I see queenless hives coming out of Winter I figure that the hive had an old queen that ran out of sperm to fertilize eggs and between the cold weather and lack of drones at that time of year it was impossible for the colony to successfully replace her. However, in the past two years some of the queenless hives that I know went into Winter with a queen that looked and acted fine, were headed by a new queen that had not even lived a full year yet. The lack of unsealed brood and eggs but capped brood in hives, indicates that the queen failed within two weeks of me inspecting the colony.
At that time of year, the queenless condition of the hives I am observing could not have been due to swarming, and it is very unlikely that something was biologically wrong with the queen. My experience has proven that creating queens with walk away splits, which is typically successful an average of 80-90 percent of the time, almost always produces a good queen.
Vermont’s Champlain Valley where my apiaries are located is saturated with honey bee hives that provides ample drone populations to help ensure excellent mating of new queens. Our destabilized climate sometimes results in prolonged stretches of cold and rainy weather that can potentially prevent virgin queens from mating successfully. However, when a new queen is not good, the workers in the colony will usually attempt to supersede her within weeks of the new queen starting to lay eggs. It is unusual for colonies headed by naturally mated queens that are nine or ten months old to fail and be superseded. Something else is going on here.
Historically, honey bee queens easily lived for 3-4 years and sometimes longer. Today we have plenty of information on how agricultural pesticides harm queens (DeGrandi-Hoffman et al., 2013; Walsh et al., 2020; Williams et al., 2015; Wu-Smart & Spivak, 2016). I suspect that what beekeepers are observing when queens fail to live even just a year or two, is the result of an Environmental Protection Agency that has failed to live up to its stated goals and ideals.
Large beekeepers are typically trying to manage so many colonies that they have to cut corners, especially with regard to labor. This is why according to a recent USDA paper that is yet to be peer reviewed, it appears that a large percentage of the past year’s losses are from commercial operations that relied too heavily on Amitraz as a quick fix to control varroa. The mites appear to have developed resistance to the treatment and acted as vectors to spread viruses among the colonies (Lamas et al., 2025) However, Varroa was rampant in the U.S. prior to the devastating colony losses caused initially by CCD and beekeepers were not regularly losing 30-60 percent or more of the hives annually like they are today. The real question we need to answer is what is damaging the immune systems of our colonies to the point where they become so vulnerable to the viruses spread by varroa?
Ultimately, the most serious problem faced by managed honey bees is not varroa mites or even the climate crisis, since we have the ability to take steps to protect our hives from the worst effects of these challenges (whether we do or not is another issue entirely). Our most serious problem is the effects of pesticides, the regulatory Swiss cheese that fails to adequately protect our bees from the immune compromising impacts of pesticides, and our limited ability to prevent and mitigate the collateral damage from the economic poisons of agriculture. The colony losses caused by chemical resistant mites are just another facet of our pesticide problem.
References:
Czechofsky, K., Westphal, C., Paxton, R.J., Hass, A. L. (2025) Landscape-level synergistic and antagonistic effects among conservation measures drive wild bee densities and species richness, Journal of Applied Ecology, https://doi.org/10.1111/1365-2664.70074
DeGrandi-Hoffman, G., Chen, Y., & Simonds, R. (2013). The effects of pesticides on queen rearing and virus titers in honey bees (Apis mellifera L.). Insects, 4(1), 71-89.
Hallmann, C. A., Sorg, M., Jongejans, E., Siepel, H., Hofland, N., Schwan, H., Stenmans, W., Müller, A., Sumser, H., Hörren, T., Goulson, D., de Kroon, H. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas, PLoS One 12(10):e0185809
Janzen, D. H., Hallwachs, W. (2021) To us insectomers, it is clear that insect decline in our Costa Rican tropics is real, so let’s be kind to the survivors, Proceedings of the National Academy of Sciences of the United States of America (PNAS), 118 (2) e2002546117
Lamas, Z.S., Rinkevich, F., Garavito, A., Shaulis, A., Boncristiani, D., Hill, E., Chen, Y.P., Evans, J.D. (2025) Viruses and vectors tied to honey bee colony losses, BioRxiv, doi: https://doi.org/10.1101/2025.05.28.656706
Lister, B.C. and Garcia, A. (2018) Climate-driven declines in arthropod abundance restructure a rainforest food web, Proceedings of the National Academy of Sciences of the United States of America (PNAS), 115 (44) E10397-E10406
Mares, B. & Conrad, R. (2020) The land of milk and honey: A history of beekeeping in Vermont, Green Writers Press, Brattleboro, Vermont
Sánchez-Bayo & Wyckhuys (2019) Worldwide decline of the entomofauna: A review of its drivers, Biological Conservation, 232: 8-27, https://doi.org/10.1016/j.biocon.2019.01.020.
Walsh, E. M., Sweet, S., Knap, A., Ing, N., & Rangel, J. (2020). Queen honey bee (Apis mellifera) pheromone and reproductive behavior are affected by pesticide exposure during development. Behavioral Ecology and Sociobiology, 74, 1-14.
Williams, G. R., Troxler, A., Retschnig, G., Roth, K., Yañez, O., Shutler, D., … & Gauthier, L. (2015). Neonicotinoid pesticides severely affect honey bee queens. Scientific reports, 5(1), 14621.
Wu-Smart, J., & Spivak, M. (2016). Sub-lethal effects of dietary neonicotinoid insecticide exposure on honey bee queen fecundity and colony development. Scientific reports, 6(1), 32108.
