Colony Strength to Prepare for Overwintering Hives

This time of year is extremely important for ensuring honey bee colonies are strong enough to survive winter. Understanding population size, weight required, stores, queen performance and disease status all influence a colony's ability to survive the winter. Assessing hives in the late summer and early fall allows beekeepers to make informed decisions that set colonies up for success throughout the long Maritime winter.

Colony Strength to Prepare for Overwintering Hives

It is important to assess colonies after supers have been removed, cleaned and stored in late summer, which is when colonies are preparing for winter. During this period, beekeepers should evaluate disease, mite levels, queen performance, population size, and winter stores. Colonies should be treated for Varroa mites and show no signs of Varroa mites or symptoms of viruses, and queens should display consistent brood patterns with healthy larvae and eggs. 

A strong population is essential in the fall. Colonies should enter winter with eight frames of bees to successfully overwinter.  To clarify, this should be eight total frames when considering all the frames within the hive as combined.  This threshold matters because smaller colonies struggle with thermoregulation, food access, and brood rearing ¹. A large cluster of bees maintains heat more effectively, reaches across frames to access honey stores, and supports the colony through long cold periods.  

Fall inspections for overall colony strength and health are important (ATTTA(C)2026).

Food stores are another critical factor, especially in the Maritime provinces where long, cold periods prevent bees from accessing food. Making sure there is enough honey and food stores is essential for maintaining heat and supporting spring buildup. Colonies require 27 – 36 kg (60-80lbs) of total honey/feed stores, including one deep full of honey (approximately 23kg/50 lbs), and if wintering two deeps, honey must be present in both. Colonies also require a good quantity of pollen to support early spring brood rearing, because natural pollen does not appear until around April. Without sufficient pollen, colonies may struggle to rear brood during late winter and early spring, which can slow buildup and weaken the colony heading into the new season. Supplemental feed can be provided to help colonies survive winter. Pollen patties can support late-season brood rearing, and fondant or 2:1 sugar syrup can be used to provide additional carbohydrates when colonies are light.  

A simple but effective way to judge winter stores is the heft test, which involves lifting the back of the hive to estimate weight. If the hive feels heavy and difficult to lift, the colony likely has enough food for winter. If it feels light, additional feeding is required. Doubles should weigh approximately 45 – 55kg (100-120lbs), and singles should be 35 – 40kg (80-90lbs).

Preliminary winter loss data from the Canadian Association of Professional Apiculturists highlights the importance of ensuring colonies enter winter with adequate stores and proper strength. Early results from the 2025-2026 season show a national loss of 34%, and in the Maritime provinces, winter losses of 50% in Prince Edward Island, 37% in Nova Scotia, and 27% in New Brunswick ². These numbers do not include confirmed causes but emphasize how vulnerable colonies can be when entering winter without proper resources. 

 

Written by Kaitlyn Newton, ATTTA Seasonal Apiculturist

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email attta@perennia.ca

 

References:

1. Sammataro, D. and Avitabile, A. 2021. A Beekeeper’s Handbook: Fifth Edition. Cornell University Press

2. Chapman et al. 2026. Preliminary Report on Honey Bee Wintering Losses in Canada (2026). 

 

Fumigating Hives with Acetic Acid

Maintaining sanitary hive equipment is important for disease management in beekeeping. Routine cleaning and replacement removes old wax, propolis, and debris, but certain pathogens can persist on hive surfaces and weaken colony health. Acetic acid fumigation is an effective way to chemically sterilize used equipment, particularly when colonies show signs of chronic infection or poor health. 

Fumigating Hives with Acetic Acid

Acetic acid (CH₃COOH) is commonly found in vinegar, but the concentration used for hive fumigation is significantly stronger. When fumigating equipment, an 80% acetic acid solution is recommended ^1,2. This strength of acetic acid is classified under Canadian WHMIS as a Flammable Liquid (Category 3), Skin Corrosion (Category 1), Serious Eye Damage (Category 1), and Acute Toxicity (Inhalation, Category 3) ³. These classifications reflect the hazards associated with this chemical and highlight the need for careful handling during fumigation. 

Vairimorpha (formerly Nosema) is a microsporidian disease that infects the midgut of honey bees. Spores are shed in fecal material and accumulate on hive surfaces, including comb, frames and hive walls. Vairimorpha spores can remain viable for up to a year in honey and fecal material and can cause a detectable infection at a low number of spores ^4,5,6. Since spores persist in the environment, they can cause reinfection of the disease in an apiary for extended periods. Periodically fumigating all equipment destroys the spores living in the environment, and supports healthier colonies when equipment is reused. Acetic acid fumigation is also effective against wax moth of all life stages when equipment is being stored⁷.

Acetic acid fumigation, however, does not kill Paenibacillus larvae, the causative agent of American foulbrood (AFB) ^1,2. AFB spores are exceptionally resilient and can survive in hive materials for decades. Equipment contaminated with AFB cannot be disinfected using acetic acid and must be destroyed according to regulatory guidelines. 

Because 80% acetic acid is corrosive, flammable, and hazardous to inhale, appropriate personal protective equipment is required. Recommended protective equipment includes chemical-resistant gloves, goggles/face shield, a respirator suitable for acid vapors, and protective clothing. 

There are two methods commonly used in beekeeping to fumigate equipment. The indoor method requires an isolated room heated to 25-30 °C ¹. Four boxes with frames should be stacked tightly on a closed pallet with no bottom boards, sealed with tape to ensure close contact between boxes, and covered with an inner cover ¹. A tin container containing 500 mL of 80% acetic acid should then be placed on the top of frames, with an empty super on the very top ¹. The acid will take approximately a week to evaporate ¹. The room should remain closed, with warning signs placed to prevent exposure to the fumes ¹. After fumigation, let the equipment air out for several days before using ¹.

The outdoor method is similar to the indoor method previously described. Ensure the stack of boxes is sealed as tightly as possible with vapor barrier plastic, stretch wrap, or tape ¹. Place the stack in an area with no wind and full exposure to the sun and only fumigate outside when temperatures are between 20-30 °C ¹. 

Fumigation with acetic acid is an effective sanitation tool for beekeepers managing hives with chronic exposure to Vairimorpha spp. When paired with other biosecurity measures and proper hygiene, fumigation can reduce environmental spore load and support healthier colonies. Caring for honey bees includes caring for the equipment they depend on!

 Written by Kaitlyn Newton, ATTTA Seasonal Apiculturist

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email attta@perennia.ca

 

References:

1. Kelly, P., n. d. Fumigating with Acetic Acid to Decontaminate Brood Chambers. Honey Bee Research Centre, University of Guelph. Available at https://hbrc.ca/acetic-acid-fumigation-2/ (Accessed August 21 2026)

2. Meredith, B., Parkinson, B. and Walker Bravo, A., 2024. Thriving Hives: Cleaning and Sterilizing Beekeeping Equipment.

3. Workplace Hazardous Materials Bureau, Health Canada, 2025. Hazardous substance assessment - Acetic acid. Government of Canada. Available at https://www.canada.ca/en/health-canada/services/environmental-workplace-health/occupational-health-safety/workplace-hazardous-materials-information-system/hazardous-substance-assessments/acetic-acid.html (Accessed August 21 2026)

4. Sammataro, D. and Avitabile, A. 2021. A Beekeeper’s Handbook: Fifth Edition. Cornell University Press

5. MacInnis, C.I., Keddie, B.A. and Pernal, S.F., 2020. Nosema ceranae (Microspora: Nosematidae): a sweet surprise? Investigating the viability and infectivity of N. ceranae spores maintained in honey and on beeswax. Journal of Economic Entomology, 113(5), pp.2069-2078.

6. McGowan, J., De la Mora, A., Goodwin, P.H., Habash, M., Hamiduzzaman, M.M., Kelly, P.G. and Guzman-Novoa, E., 2016. Viability and infectivity of fresh and cryopreserved Nosema ceranae spores. Journal of microbiological methods, 131, pp.16-22.

7. National Bee Unit, 2025. Fumigating Comb. Available at https://www.nationalbeeunit.com/assets/PDFs/3_Resources_for_beekeepers/Fact_Sheets/Fact_14_Fumigating_Comb.pdf(Accessed August 21 2026).