Nosema Control Products

Nosema disease control products are products used, or sold for use, against the spores of Nosema apis and Nosema ceranae (now called Vairimorpha), which settle in the gut of adult bees. The medicine used in the past (fumagillin) is no longer authorised in many countries today, and evidence for the effectiveness of herbal and probiotic products sold as "nosema support" is limited. The real tools of Nosema control are diagnosis with a microscope, comb renewal, comb disinfection, good nutrition and clean water.

Diagnosis first: Nosema cannot be recognised by eye

Nosema symptoms are not specific. N. apis mostly shows itself in late winter and spring with dysentery streaks; N. ceranae, however, can be present all year and often weakens the colony silently without causing streaks. Seeing faecal streaks in front of the hive does not prove Nosema, and not seeing them does not rule it out. That is why diagnosis with a microscope is essential before using any product.

Counting spores with a microscope

1. Take a sample of about 30 bees from old foragers returning to the entrance; young house bees can make the result look better than it is.
2. Crush the bees' abdomens with a little water and put a drop on a slide.
3. At 400× magnification look for bright-edged, oval spores resembling grains of rice; measure their density with a counting chamber.
4. A molecular test (PCR) in the laboratory is needed to reliably tell N. apis from N. ceranae.

Taking samples at least twice a year, at the start of spring and in autumn, lets you see the trend. If you have no microscope, preserve the bee sample in alcohol or by freezing and send it to a laboratory; ask in advance which bees to send, how many and how.

Is there a Nosema treatment? Product groups and the state of the evidence

In short, for Nosema there is no widely authorised product that is given to the bees in the hive and reliably cures the disease. Ask your veterinarian whether there is an authorised option in your country and about restrictions relating to the honey harvest. Do not use antibiotics or mixtures recommended on the internet on your own; they leave residues in honey and do not solve the problem.

Comb disinfection: acetic acid and comb renewal

Nosema spores accumulate on comb with faeces and become a source of reinfection the following season. That is why the most effective "control product" is in fact clean comb.

• Comb renewal: Every year remove some of the old, darkened combs and give foundation. Take faeces-soiled combs out of circulation gradually.
• Acetic acid fumes: Empty, honey-free combs left from diseased or dead colonies can be disinfected with acetic acid fumes in a closed stack of boxes. The acid is corrosive; use gloves, goggles and a mask, work in the open air away from bees, and protect metal parts. Air the combs thoroughly before putting them back in a hive.
• Hive body and floor: Clean them by scraping; wooden surfaces can be scorched with a flame.
• Comb exchange: Do not give frames from a diseased colony to healthy colonies.

Support against Nosema: nutrition and water

The damage Nosema does to a colony increases markedly when combined with varroa, viruses, poor nutrition and pesticide exposure. So fix the basic conditions before reaching for support products:

1. Nutrition: Give syrup in good time during a nectar dearth, and pollen or pollen substitute in spring if pollen is short. Make sure the winter stores are not dominated by hard-to-digest honeydew honeys.
2. Clean water: Set up a clean, frequently refreshed water source near the apiary; stagnant, dirty shared water sources can spread spores.
3. Keep varroa under control: This is the most important step in reducing the overall pressure.
4. Damp and ventilation: Keep the hive tilted slightly forward and off the ground; a damp hive makes the N. apis problem worse.
5. Young queen and strong colony: Requeen colonies with persistent recurrence, and unite weak colonies once the diagnosis is clear.

What should you look for when buying a support product?

• Authorisation or registration: Does the product have a veterinary product authorisation, or is it only a feed additive? Do not trust a product that claims to "cure" but has no authorisation.
• Ingredients: The active ingredients and their amounts should be clearly stated; a "secret formula" claim is a warning sign.
• Honey harvest warning: Can it be used while supers are on, and is there a withdrawal period?
• Independent trials: Is there an independent field study apart from the manufacturer's brochure?
• Your own measurement: If you use it, have spore counts done before and after to see whether it works.