by Véto-pharma New data about high honey bee colony losses in the United States from June 2024 until March 2025 come from two surveys, answered by hundreds of commercial, sideliner, and hobbyist beekeepers across the country.1 The upcoming publication sheds some light on the underlying causes of the excessive colony losses reported earlier this year. Specifically, hive management practices (including varroa treatment strategy and feeding practices), seasonal and weather-related dynamics, and environmental factors (pesticides) appear to be of some relevance according to the responses given by beekeepers.1
The data from two surveys initiated by Project Apis m. (PAm) and the American Beekeeping Federation (ABF) show that commercial beekeepers who did not specify the type of miticide they used experienced significantly higher net colony losses compared to those who reported using amitraz-based products, non-amitraz miticides, or a combination of both.1 Losses among beekeepers using only non-amitraz products were comparable to those using amitraz, suggesting that varroa mite resistance to amitraz may not have been the main driver of high colony loss rates, after all.1
Dr. Claudia Garrido came to a similar conclusion in her recent article: “Now it gets really interesting, especially concerning the paper I discussed last time: The losses did not (NOT!) relate to the use of amitraz. Though it is widely used between commercial beekeepers, treating with amitraz or something else did not influence the colony losses. This confirms what I said in my previous post: The claim that amitraz resistance was not supported by this survey. In my opinion, that claim was a massive overinterpretation.”
Further, no significant differences in colony losses were observed between beekeepers who felt their treatments were effective and those who did not.i This finding highlights the need for regular and systematic varroa mite monitoring throughout the season for more precise assessments of treatment impact on colony survival. Among hobbyists, those who did not use miticides observed higher losses than those who used non-amitraz products, further emphasizing the importance of active varroa management.1
Overall, those results from the surveys specifically related to varroa treatment strategy, confirm previous findings on the effects of hive management practices on colony mortality. A longitudinal study by Underwood et al. (2023) compared conventional, organic, and miticide-free management strategies over three years, revealing that colonies managed conventionally or organically had survival rates nearly three times higher than those under miticide-free management, with significantly better honey production and pathogen control.2
In addition, the importance of regular varroa mite monitoring has been increasingly emphasized in recent publications as a cornerstone of effective colony management. A 2025 study by Boehm Vock et al. demonstrated that while treating against varroa mites is beneficial, treatments applied without prior monitoring were no more effective than not treating at all.3 This finding strongly supports Integrated Pest Management (IPM) principles, where monitoring guides timely and targeted interventions.3
In the two colony loss surveys by PAm and the ABF, sideliners who provided limited supplemental feeding (proteins only once and carbohydrates fewer than four times annually) experienced higher losses, suggesting that nutritional support plays a critical role in colony resilience.1 This observation aligns with a growing body of research highlighting the detrimental effects of malnutrition on honey bee health. For instance, Castaños et al. (2023) demonstrated through lipidomic and gene expression analyses that nutritional stress, particularly diets lacking protein, triggered metabolic shifts in bees, including increased lipid mobilization and altered fat body composition, which compromised colony productivity and long-term survival.4
The availability of diverse, high-quality pollen is essential to the colony, as it supports immune function, larval development, and the synthesis of vital proteins like vitellogenin, which are linked to longevity and disease resistance (Di Pasquale et al., 2013; Ricigliano et al., 2022).5-6 These findings underline that supplemental feeding, particularly protein feeding during pollen-scarce periods, is not merely a supportive measure but a vital strategy for maintaining colony health and resilience against environmental and biological stressors.
Survey questions about seasonal loss rates revealed that summer losses were predictive of winter losses, particularly among commercial beekeepers with consistently low overall losses.1 On the other hand, the data also demonstrate variability between summer and winter loss rates in other beekeeping operations, instead of just showing high net losses across the board.1 Past studies have found that elevated summer losses often precede high winter mortality, indicating that summer colony health can be a strong predictor of overwintering success. For example, Gray et al. (2024) demonstrated that poor summer forage availability and high parasite loads, particularly Varroa destructor, were associated with reduced winter survival across a range of weather conditions.7
Additionally, warmer autumns and winters, linked to climate change, can disrupt the age structure of overwintering clusters, skewing populations toward older bees and increasing spring mortality.7 Identifying specific management practices or environmental factors that resulted in lower overall colony losses among this subgroup of commercial could offer valuable insights regarding the causes of high loss rates in the United States.
While Varroa mites were most frequently cited as the cause of colony losses by all beekeepers, other factors such as regional weather events and pesticides were often mentioned as well.1 While commercial beekeepers cited pesticides more frequently as a potential cause of colony losses, hobbyist beekeepers cited the (local) weather more often.1
Researchers have become more interested in weather- and climate-related effects on honey bee health and colony survival in recent years. Calovi et al. (2021) found that summer temperatures as well as precipitation during the warmest quarter of the preceding year were the strongest predictors of overwintering survival, emphasizing the importance of summer weather in shaping colony resilience.8 Rajagopalan et al. (2024) used climate simulations to show that warmer autumns and winters can skew the age structure of overwintering clusters toward older bees, increasing spring mortality and leading to colony collapse.9
Their findings also suggest that indoor cold storage may mitigate some of these climate-induced risks.9 Frunze et al. (2024) demonstrated that elevated ambient temperatures during late summer and fall disrupt the physiological transition to long-lived winter bees, leading to premature aging and reduced survival.10 Looking at the summer and fall of 2024, temperatures across the United States were exceptionally high with some regions experiencing persistent heat waves.11 Precipitation varied regionally in 2024 with parts of the country exposed to draughts and unusually high levels of precipitation in other regions.11 Potential effects on honey bee health, specifically but not exclusively on varroa mite infestation build-up should not be ruled out.
Pesticide exposure, on the other hand, is more difficult to quantify and trace due to the diversity of compounds, application methods, and environmental persistence. Nonetheless, it has been increasingly recognized as a significant contributor to honey bee colony mortality. Unlike varroa mites or weather events, pesticide impacts are often subtle and cumulative, involving a wide range of compounds and exposure routes. Recent studies have shown that even sublethal doses of neonicotinoids can impair neural function, suppress immunity, and disrupt foraging behavior, ultimately weakening colony cohesion and resilience (Singh & Rana, 2025).12 These effects can be magnified when pesticides are present in mixtures, as demonstrated by Migdał et al. (2023), who found that combinations of glyphosate, acetamiprid, and tebuconazole altered detoxification enzyme activity and increased mortality in worker bees.13 These findings emphasize the need for integrated pest and land management strategies that consider not only acute toxicity but also chronic and synergistic effects. As highlighted by Tsvetkov et al. (2017)14 and Colin et al. (2019)15, pesticide exposure in agricultural landscapes can significantly reduce colony survival, especially when combined with poor nutrition and climate stressors.
The surveys initiated by Project Apis m. (PAm) and the American Beekeeping Federation (ABF) exemplify how essential it is to include beekeepers directly in the investigation and discussion of severe colony loss events. Their firsthand observations and experiences provide critical context for interpreting scientific data and identifying emerging threats to colony health. By capturing a wide range of management practices, environmental exposures, and regional conditions, these surveys offer a nuanced understanding of the multifactorial nature of colony losses. Moreover, they empower beekeepers to contribute to evidence-based solutions and adaptive strategies tailored to real-world challenges. As the beekeeping community continues to face evolving pressures, collaborative efforts between researchers and practitioners will be vital for developing resilient and sustainable approaches to honey bee health.
1- Nearman, Anthony, et al. “Insights from US beekeeper triage surveys following unusually high honey bee colony losses 2024-2025.” bioRxiv (2025): 2025-08.
2- Underwood, Robyn M., et al. “Organic colony management practices are profitable for backyard beekeepers.” Journal of Economic Entomology (2025): toaf133.
3- Boehm Vock, Laura, et al. “Spatiotemporal, environmental, and behavioral predictors of Varroa mite intensity in managed honey bee apiaries.” Plos one 20.8 (2025): e0325801.
4- Castaños, Clara E., et al. “Lipidomic features of honey bee and colony health during limited supplementary feeding.” Insect molecular biology 32.6 (2023): 658-675.
5- Di Pasquale, Garance, et al. “Influence of pollen nutrition on honey bee health: do pollen quality and diversity matter?.” PloS one 8.8 (2013): e72016.
6- Ricigliano, Vincent A., Steven T. Williams, and Randy Oliver. “Effects of different artificial diets on commercial honey bee colony performance, health biomarkers, and gut microbiota.” BMC veterinary research 18.1 (2022): 52.
7- Gray, Darcy, et al. “Effective pest management approaches can mitigate honey bee (Apis mellifera) colony winter loss across a range of weather conditions in small-scale, stationary apiaries.” Journal of Insect Science 24.3 (2024): 15.
8- Calovi, Martina, et al. “Summer weather conditions influence winter survival of honey bees (Apis mellifera) in the northeastern United States.” Scientific reports 11.1 (2021): 1553.
9- Rajagopalan, Kirti, et al. “Warmer autumns and winters could reduce honey bee overwintering survival with potential risks for pollination services.” Scientific Reports 14.1 (2024): 5410.
10- Frunze, Olga, et al. “The effect of seasonal temperatures on the physiology of the overwintered honey bee.” PloS one 19.12 (2024): e0315062.
11- National Centers for Environmental Information (NCEI). “Assessing the US Climate in 2024.” (published: January 10th, 2025) https://www.ncei.noaa.gov/news/national-climate-202413
12- Singh, Gagandeep, and Anita Rana. “Honeybees and colony collapse disorder: understanding key drivers and economic implications.” Proceedings of the Indian National Science Academy (2025): 1-17.
13- Migdał, Paweł, et al. “Biochemical indicators and mortality in honey bee (Apis mellifera) workers after oral exposure to plant protection products and their mixtures.” Agriculture 14.1 (2023): 5.
14- Tsvetkov, Nadejda, et al. “Chronic exposure to neonicotinoids reduces honey bee health near corn crops.” Science 356.6345 (2017): 1395-1397.
15- Colin, Theotime, et al. “Long-term dynamics of honey bee colonies following exposure to chemical stress.” Science of the Total Environment 677 (2019): 660-670.
by Véto-pharma Varroa quiz – The Véto-pharma team has gathered 16 questions to test your knowledge on Varroa destructor. Do you think you don’t know anything? Maybe we will succeed in surprising
by Caroline Lantuejoul 
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