Nosema: Treatment and Management in Honey Bees

Nosema is a fungal parasite affecting honey bees, causing Nosemosis disease. It involves two microsporidian species: Nosema apis and Nosema ceranae, both posing challenges for beekeepers globally. Recently, Nosema ceranae has spread worldwide, even though Nosema apis was historically dominant in the USA and Europe. Originating with Asian honey bees, Nosema ceranae has expanded its presence internationally. Preventing losses from Nosema infections is crucial in beekeeping, and this article aims to enhance your knowledge of the disease and guide effective treatment approaches.

Impact of Nosema on Honey Bees

Nosema infections affect honey bees in multiple detrimental ways. Eventually, colonies collapse, and even abandonment of the hive often offers little relief. Prior to colony loss, forager bees fail to collect sufficient resources to sustain hive health. In particular, Nosema ceranae-infected foragers may leave foraging trips but fail to return to the hive.

After becoming infected, a bee typically survives about eight days before dying, resulting in hives with queens and nurse bees but few foragers. As foraging declines, stored honey and pollen become depleted since the bees consume these reserves more quickly than they are replenished. When the bee population falls below a viable threshold, the colony finally collapses due to the disease.

Symptoms and Diagnosis of Nosemosis

Distinguishing Nosema infection from other bee diseases can be difficult. The hallmark symptom is dysentery, alongside other factors such as seasonal timing and the presence of crawling bees. Nosema is especially prevalent in spring following inclement weather and can be detected in wintered hives when opened in spring. Worker bees are more frequently affected than drones, while queens are less often infected since sick workers typically do not feed the queen.

Recognizing Nosemosis Signs

1. Dysentery appears as fecal streaks around the hive entrance, as bees defecate immediately upon exiting the hive.
2. Affected bees often exhibit inability to fly, instead crawling outside in significant numbers.
3. Additional indicators separating Nosema from other diseases include:
4. Abdominal swelling in bees;
5. Worker bees showing no sting reflex;
6. Early replacement of the queen.

When Nosema infects the queen, her ovaries can degenerate severely, impairing egg production and leading to her early supersedure.

Confirming Nosemosis Diagnosis

Nosema ceranae inflicts more severe damage on the bees’ digestive system than Nosema apis and often lacks classical Nosema symptoms. Diagnoses involve microscopy, bee dissection, and molecular methods. In advanced infection stages, the bee’s ventriculus appears enlarged and pale.

To detect spores, infected bees may be macerated in water and the resulting suspension examined microscopically. However, distinguishing spores of Nosema apis from Nosema ceranae by light microscopy is unreliable. Electron microscopy offers definitive spore identification, while PCR analyses can detect Nosema DNA and accurately differentiate both species.

Nosema Treatment Products

1. Fumagillin for Honey Bees

Fumagillin is widely used to treat Nosema in honey bee colonies and is considered the most effective available option. This natural compound is derived from fungi found in soil and decomposing organic material and is marketed under names like Fumagillin-B and Fumidil-B. It is administered to bees via feed or water, where it inhibits spore development and multiplication within the bees’ guts. Importantly, while it suppresses growth, Fumagillin does not kill existing Nosema spores.

Correct application of Fumagillin is essential; following label instructions precisely is crucial. Excessive doses can harm bees and contaminate hive products, whereas insufficient doses may fail to effectively control the disease.

Exploring Alternatives to Fumagillin

Ongoing research aims to discover alternatives to Fumagillin, with beekeepers encouraged to support such studies by allowing field trials and contributing resources. These efforts benefit researchers, beekeepers, and agricultural authorities by advancing the knowledge and tools available to manage Nosema.

2. Honey B Healthy Nosema Treatment

HoneyBHealthy® is a solution containing emulsified lemongrass and spearmint oils marketed to control Nosema. Some beekeepers report success feeding this product to their bees, typically administered in syrup form to encourage consumption. However, comprehensive scientific evidence supporting its effectiveness against Nosema is limited.

3. ApiHerb and Vita Feed Gold

ApiHerb and Vita Feed Gold are two similar products prevalent in Western Europe for combating Nosema in honey bees, both supported by evidence demonstrating their effectiveness. Vita Feed Gold, marketed as a fortified liquid feed for bees, is produced by the same company that offers Vita Feed Green, a product rich in essential oils designed to strengthen colonies and control chalkbrood. ApiHerb is produced by the makers of Apilife Var, which targets Varroa mites in bee colonies.

4. Nozevit

In Central Europe, beekeepers use Nozevit to prevent Nosema infections in their hives, especially valuable for overwintering bees. This product contains extracts derived from tree bark and is also authorized by the FDA for use in the USA, making it suitable beyond its European origins.

Natural Approaches to Treating Nosema Infestation

Fumagillin remains the most effective treatment for Nosema fungal infections, yet various natural remedies have been explored with mixed results. Incorporating alternatives alongside Fumagillin helps reduce the risk of the fungus developing resistance and addresses concerns about chemical residues in hive products. Additionally, combining treatments offers flexible options to manage Nosema in honey bee colonies tailored to specific needs.

Plants synthesize numerous compounds in their barks and saps, providing a rich source for natural disease treatments. Many plant-derived substances, including essential oils, are employed in beekeeping to treat illnesses, combat parasites, and repel pests from hives, appearing in different forms such as extracts and oils.

Among promising natural remedies, thymol and resveratrol from red grape skins stand out. Besides curbing Nosema, thymol also inhibits fungal growth in bee feeders and proves effective against other bee parasites like mites. Research trials consistently show thymol outperforming other natural agents in controlling Nosema.

Thymol Syrup Preparation for Nosema Control

To prepare a thymol-infused syrup for treating Nosema, follow this recipe:

1. Use ethyl or isopropyl alcohol as the base since alcohol dissolves thymol crystals far better than water. Once the alcohol solution is made, water can be added to achieve the desired volume. Avoid using denatured alcohol.
2. Starting with the thymol crystals, measure 12.5 grams and dissolve them into 88 ml of alcohol to create approximately 100 ml of a premixed solution.
3. When making the final thymolated syrup, add 2 ml of this premix to each gallon of syrup, which equals about 2 teaspoons per 5 gallons of water. Thorough stirring is essential to ensure the thymol is evenly dissolved. The presence of alcohol aids this dissolution; uneven mixing can concentrate thymol unevenly and harm the bees.

Precautions When Handling Thymol

Thymol can cause irritation to skin and eyes. Protective measures include wearing nitrile gloves and avoiding contact with facial areas such as mouth, eyes, ears, or mucous membranes during handling. Always wash hands thoroughly after working with thymol. If exposure occurs on skin or eyes, rinse immediately with plenty of warm water, as cold water does not effectively remove thymol.

Tea Tree Oil as a Remedy for Nosema

Tea tree oil offers a natural alternative for managing Nosema, either used alone or combined with oils like spearmint and lemongrass. When mixed with other essential oils in feeding syrup, tea tree oil is typically included in smaller amounts, but higher quantities may be used if it is the sole oil present. Care is necessary to avoid toxicity to honey bees, as excessive levels can be harmful. Additionally, always wash your hands after applying any treatment for pests or diseases in your apiary.

Here is a straightforward recipe to make a tea tree oil treatment for Nosema:

1. Begin by mixing approximately 1 teaspoon of tea tree oil with half a cup of water.
2. Then add this mixture to half a gallon of water.
3. From that diluted mix, measure 1 cup and combine it with a gallon of 1:1 sugar water syrup, resulting in a concentration that is safe for bees but effective against Nosema.

It is essential to use pharmaceutical-grade tea tree oil for this treatment, as essential oils used in perfumery may lack the purity required to provide the desired medicinal effects.

Treatment for Nosema Apis

Nosema Apis is one of the two fungal species infecting honey bees, showing somewhat different symptoms from Nosema Ceranae. Traditionally, Fumagillin has been used to inhibit spore growth of Nosema Apis. Further decontamination of hives and equipment can be achieved using formaldehyde, acetic acid, or physical methods like gamma or ultrasonic radiation where available. For beekeepers, applying heat at 490°F (approx. 254°C) for 24 hours is a recommended method to sanitize contaminated materials.

Treatment for Nosema Ceranae

Managing Nosema Ceranae remains challenging due to its relatively recent identification in Europe and North America. Limited research has been conducted in North America, so no definitive treatment exists yet. Beekeepers employ a variety of strategies ranging from natural remedies to dilute acids aimed at mitigating the disease’s effects and transmission.

While Fumagillin is an effective treatment for Nosema Apis, it should not be used for Nosema Ceranae. In fact, Fumagillin can worsen Nosema Ceranae infections by accelerating fungal growth and spore production, with studies noting a doubling of spores shortly after treatment.

Is Nosema Contagious?

Young honey bees emerging within a colony are initially free from Nosema infection, even if the colony is infected. Infection occurs only after bees ingest Nosema spores. Transmission primarily happens through oral contact or fecal-oral routes. Some research also suggests potential sexual transmission.

Within a beehive, Nosema spreads rapidly among bees, but natural transmission between separate hives in an apiary is less straightforward. Often, beekeepers inadvertently facilitate Nosema’s spread from one hive to another via contaminated tools, equipment, or hive parts.

Once a honey bee ingests Nosema spores, these spores quickly germinate and invade the epithelial cells lining the bee’s ventriculus. Inside these cells, Nosema enters its vegetative phase, during which it grows and multiplies, disrupting the cell’s RNA production. Within six to ten days, the infected cells become loaded with new Nosema spores, eventually detaching into the ventriculus. There, the cells rupture, releasing spores and digestive enzymes that can infect other bees, thereby facilitating the spread of infestation within the hive.

Post-Nosema Infestation Cleanup

After a Nosema outbreak, it’s essential to thoroughly clean and treat beehives, a demanding but necessary process. Prevention is always preferable, so confirming that Nosema is indeed the cause of infection in your colony before starting is crucial. Accurate diagnosis can save time and ensure appropriate actions are taken during cleanup.

• Microscopic examination is often sufficient for identification, though samples can also be sent to specialized laboratories for confirmation.
• Nosema spreads through hardy spores that resist drying and moisture, which bees ingest when sharing food and performing hive maintenance like cleaning old combs.
• Infected bees’ feces harbor Nosema spores, posing a risk to other bees that clean hive surfaces, thereby perpetuating the infection cycle.

Thorough Cleaning Procedures

After a Nosema outbreak, every component of the affected hive must be meticulously cleaned, often requiring disassembly. Fumigation and scorching are popular methods to sanitize equipment and prevent reinfection. Wooden parts such as the hive body, bottom boards, and inner cover should undergo these treatments after removing any residual debris. It’s also important to sanitize all tools used during the cleaning process to avoid spreading spores.

Applying Fumigation

Various chemicals can be used for fumigating Nosema-contaminated equipment, but only those approved by regulatory authorities should be employed. Due to practicality issues, hobbyists and small-scale beekeepers often find heat treatment more feasible. Although challenging, heat treatment is effective if carried out properly. Because Nosema spores are resilient, sustained exposure to specific temperatures is required: at 400°C, hive parts must remain heated for at least five days; at 490°C, 24 hours; and at 600°C, treatment can be as brief as 15 minutes.

Strategies to Prevent Nosema Infections

It’s far better to prevent Nosema infection than to treat it once established, as controlling the disease in affected colonies is complicated. Robust, populous colonies tend to resist Nosema longer, delaying widespread infection. Regular hive inspections are key to early detection and managing the disease effectively.

Consider these recommendations to reduce the risk of Nosema in your hive:

1. Proper ventilation helps maintain moisture levels that deter fungal growth, making the hive environment less hospitable to Nosema.
2. Ensuring colonies enter winter strong and well-supplied with food makes them less vulnerable to Nosemosis.
3. Treating for other diseases and pests keeps the colony healthy, as weakened bees are more prone to Nosema infection.

Sunlight Exposure and Cleansing Flights During Winter

Positioning beehives to maximize winter sunlight encourages bees to take short cleansing flights, which help them expel feces outside the hive. This natural sanitation limits moisture buildup and reduces the risk of Nosema infection, since fecal matter inside the hive can increase moisture and create favorable conditions for the fungus.

Maintaining hive cleanliness is crucial year-round. Although bees regularly clean their home, beekeepers can assist during inspections by removing debris and unwanted materials to support overall hive hygiene.

Summary

Nosemosis, caused by a microsporidian fungus, poses a significant threat to beekeeping by potentially causing substantial losses. Early detection allows for timely control measures. Fumagillin is effective against Nosema apis infections but does not work against Nosema ceranae.

Alternative treatments using natural substances, such as various oils, have shown promise, especially against Nosema ceranae. Ultimately, preventing the spread and growth of Nosema spores by maintaining a dry, well-ventilated hive, even during winter, remains the most effective defense strategy.