How to Identify and Treat Nosema in Honey Bees

January 25, 2025

Pollination forms a vital part of the natural life cycle, where honey bees rank as top pollinators to many plants and crops. Essentials to bee health and survival, diseases interfere with normal behaviours, foraging, communication, and reproduction. If the bees are not treated, life-threatening conditions can completely wipe out a colony. Nosema is the most common and destructive disease in honeybees, a fungal infection that feeds on pollen in their digestive system and leaves them starving. Eventually, colonies decline, as do honey yields.

This is a comprehensive guide, intended for those who are new to honey bees, who might be wondering how to detect and treat Nosema, if you know what to look for in nosema symptoms. In this article, we will explain how to recognize, diagnose, and treat this viral disease, as well as how to prevent it as beekeepers in order to sustain strong and healthy colonies.

What is Nosema?

Nosema is a gut parasite infectious disease with associated microsporidian fungi infecting the gut of honey bees. Bee-damaging species There are two primary types responsible for honeybee damage:

1. Nosema apis – More endemic to the cooler climates, generally affects only older adults.

2. Nosema ceranae — More virulent and widespread, capable of infecting bees in any season and usually causing colony collapse if untreated.

These two species interfere with digestion and suppress the immune response and diminish the life span of infected bees, resulting in losses to the colony if not controlled.

How Does Nosema Spread?

Transmission routes of Nosema spores are efficient both within and between colonies, and occur chiefly by:

✔ Contaminated food and water – Nosema spores are consumed by bees when they feed on infected honey, pollen, or water.

✔ Functional bee-to-bee contact: Spores can be transferred between bees via feeding, grooming, or trophallaxis (food swapping).

✔ Infected hive equipment – Infected frames, combs or tools are a source of infection for other hives.

✔ Dysentery (Bee Diarrhea) – Spores from Nosema-infected bees show up in their feces, polluting the hive and food sources.

Since Nosema has such a high transmission rate, early diagnosis and treatment are essential to prevent high-level epidemics.

Detecting Nosema infection: Signs & Symptoms

Nosema is often referred to as a silent killer because no obvious signs are presented in infected colonies until the disease is well progressed. That said, there are a few warning signs to look out for:

1. Decreased Bee Activity

You see weak sluggish bees and less foraging activity.
Declining Worker Bees Back to Hive

2. Dysentery (Bee Diarrhea)

Bright yellow or brown poop stains outside the hive.
Inappropriate defecation of bees in the hive / outside

3. Early Queen Failure

The queen either ceases laying eggs or produces an erratic brood pattern.
She can be prematurely replaced by the colony.

4. Low Brood Production

Less egg and larva production causing colony death
Weak colonies, even when foraging at high rates.

5. Shortened Lifespan of Bees

Worker bees that die early are relevant because they are first to become inmates.
Sex-Determined Foragers Reduced Honey Production

Because Nosema affects the guts of bees, it weakens them internally and it can be difficult to detect, as there are no obvious symptoms to observe externally. The best diagnosis is performed through laboratory testing.

How to See Nosema in our Honey Bees

1. Field Observation

- Look at the hive for diarrhea or fecal staining
- Look at the behavior of the bees — do they seem weak; do they stay tucked into the cluster; and were they dead before they should have died?

2. Lab Test — Microscope (Most Trustworthy Way)

With a microscope, beekeepers can inspect bee guts to confirm a Nosema infection:

Testing Bees for Nosema (here are the steps):

Gather 30-50 adult bees, preferably older foragers, from the entrance of the hive.
Add a couple of drops of water and crush the bees to recover the gut contents.
Using a microscope slide, place a very small drop of the solution
Look for Nosema spores (which look like small oval blobs) at less than 400x magnification.

Treatment is suggested if spore counts are above 1 000 000 per bee.

3. Commercial Lab Testing

While some other apiarists prefer to take your bee samples to labs for a more accurate diagnosis of the problem. Labs that can generate spore loads, as well as the severity of the infection.

What to Do If You Have Nosema in Honey Bees

Since Nosema is an immediate threat to the survival of the colony, once detected, a treatment must be applied promptly.

1. Fumagillin Utility (Medicated Treatment)

Antibiotic therapy for Nosema is limited to a single FDA-approved compound called Fumagilin-B.
This is then mixed with sugar syrup to be fed to bees in the spring or fall.

Dosage & Application:

For each gallon of sugar syrup (one part sugar and one part water), mix 1 tsp of Fumagilin-B.
Administer medicated syrup to the hive for a period of weeks until symptoms abate.

Nosema apis: fumagillin (may not be as effective against Nosema ceranae)

2. Natural and Supplementary Treatments

If beekeepers are seeking chemical-free options, there are a few natural methods which can help control Nosema infections:

✔ Serve Good Nutrition

Pollen supplement to enhance immune system
Plant flowers that are rich in nectar and pollen to provide a varied forage environment.

✔ Incorporate Essential Oils, which includes Thyme, Oregano, and Tea Tree Oils

Certain beekeepers have been known to supplement bees with sugar syrup infused with essential oils for their wellbeing.
Add 5-10 drops of essential oil per gallon of syrup and feed periodically.

✔ Vinegar/Acidified Syrup Treatment

When added to sugar syrup, apple cider vinegar or citric acid lowers the gut pH and makes life hard for Nosema.
Add one tablespoon of apple cider vinegar per gallon of syrup.

✔ Probiotics for Gut Health

Probiotics (like SuperDFM for bees) will replenish lost beneficial gut bacteria and enhance digestion.

Although natural treatments may not kill Nosema, they can mitigate the severity of infection and enhance overall colony resilience.

Ways to Avoid Nosema Infections

As Nosema is virtually impossible to eradicate once it takes hold, prevention is the best form of defence in keeping colonies in good health.

1. Keep a Clean Hive Area

✔ Clean and disinfect hive equipment periodically with diluted bleach or acetic acid.

✔ Use clean frames, since old or moldy frames or frames that have been heavily used can foster spore buildup.

2. Improve Hive Ventilation

✔ Avoid moisture accumulation between the frames using dry and ventilated hives places incidence of fungal outbreaks.

✔ Hives shall be tilted forward a little to allow water to drip.

3. Strengthen Colony Nutrition

✔ Provide bees with a wide variety of forage all year long.

✔ Ensure that when nectar is scarce, then provide protein supplements

4. Never Have Food And Water From Contaminated Sources

✔ Do not give bees old or infected honey we know it contains Nosema spores

✔ Have access to a source of clean water that is at least 30m away from stagnant/contaminated water.

5. Use Resistant Bee Strains

✔Certain strains of honey bee are more resistant to Nosema infections.

✔ Use only bee strains that you breed yourself or have bought, having tested for their hygiene and disease-resistance.

Conclusion

A serious yet manageable honey bee colony disease: Nosema. But with knowledge of its causes, early identification of symptoms and appropriate treatment methods, beekeepers can save their colonies and avoid the loss of hives.

Key Takeaways:

✔ Examine colonies for Nosema (diarrhea, weak bees, queen failure) by doing an examination soon to get the colony well ahead of any Nosema problems.

✔ Confirm - microscope testing or laboratory diagnosis,

✔ Use Fumagillin or organic treatments to lower the number of spores.

✔ Enhance nutrition, ventilation, and sanitation to avoid reinfection.

With these strategies, beekeepers will have a robust health of bee colonies keeping them active and away from diseases.