Nosema, a destructive effect caused by fungi known as Nosema apis and Nosema ceranae, can have a significant impact on beehives if left unaddressed. While Nosema apis is generally a benign parasite in European honey bees worldwide, it can cause severe damage without timely intervention.
These spore-forming parasites attack the mid-gut lining of bees, which is responsible for producing digestive enzymes for pollen digestion. As the parasites multiply and produce more spores, they feed on the epithelial cells of the mid-gut lining, reducing the efficiency of digestion and pollen absorption and weakening the bees.
When the number of spores in a cell becomes excessive, it ruptures, releasing spores into the mid-gut. Some spores may pass through the small intestine to the rectum. A heavily infested bee can harbor as many as 30-50 million spores.
Symptoms of Nosema infection can be challenging to distinguish from other diseases as they often manifest as nonspecific signs. Infected bees tend to defecate inside the hive, leaving yellow or yellowish excrement stains on frames, bottom boards, combs, and both the inside and outside of the hive. Bees infected with Nosema apis may also exhibit signs of dysentery and show decreased attention to brood rearing, with older bees taking on guard and foraging duties. Hypopharyngeal glands, responsible for producing royal jelly, lose their ability to function properly. Infected bees may crawl in front of hives with distended abdomens and spread their wings.
Nosema infection can also impair bees’ flying abilities, resulting in short-distance flights or an inability to fly altogether due to disjointed wings. The life expectancy of infected bees is typically reduced by 78%. If the queen is infected, her ovaries may degenerate, leading to a significant decline in egg production and failed larvae development.
Spread of Nosema infection occurs when non-infected bees ingest spores. Defecation inside the hive is a primary source of infection, and spore ingestion occurs when bees clean contaminated combs. Transfer of Nosema apis spores between hives can happen through the exchange of contaminated combs, hive splitting, or feeding bees honey contaminated with spores.
In spring, Nosema infection levels rapidly increase as brood rearing begins and inclement weather limits flight activity, causing bees to spend more time in the hive and defecate inside, further spreading the infection. In late spring, infection levels gradually decrease as bees regain the ability to fly and defecate outside the hive. Additionally, older infected bees die off, making room for uninfected newly emerged bees. Infection rates decline significantly during summer as the combs become cleaner.
However, the infection may persist within a colony, reemerging the following spring. Healthy European honeybee colonies can generally handle Nosema infections well when provided with proper nutrition and favorable weather conditions for flight and defecation outside the hive.
Prevention plays a crucial role in managing Nosema infestations in honeybee colonies. Beekeepers can adopt various good husbandry practices to prevent infestations effectively. Regularly feeding bees antifungal medication, such as Fumagilin-B, in gallons of heavy syrup during spring and fall is one of the best preventive measures. Placing colonies in sunny winter locations and ensuring adequate hive ventilation to avoid excess moisture can also discourage infestations.
Several methods can be employed to eradicate Nosema apis. Disinfecting contaminated combs is essential to prevent further spread within the hive. Fumigation with 60-80% acetic acid vapor can achieve this, effectively killing spores within a week. The recommended mixture is 1 part water to 4 parts glacial water-free acetic acid, applied at a temperature higher than 15°C for faster evaporation. Fumagilin-B treatment is another straightforward approach for treating infected hives, although it may not be efficient for heavily infested colonies. In cases where Nosema apis spores persist for years, complete eradication requires disposing of all living organisms in the hive and burning the equipment.
To incinerate affected equipment, create a pile including beehives, combs, honey, and bees. Dig a hole adjacent to the pile, ensuring it is at least 1 meter x 30cm in size (larger for multiple hives). Place frames containing contaminated honey around the main fire, allowing them to dry before burning to avoid stifling the fire with honey. Take necessary precautions during incineration and have fire extinguishing resources nearby. Finally, bury the ashes and remnants.
Identifying the source of infection is crucial before eradicating Nosema apis. This step enables the prevention of further spread, facilitating complete parasite eradication. Common causes of infection include swarms of infected bees, contaminated equipment (especially used equipment), uniting diseased hives with healthy ones, and visits by other beekeepers.
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