Hive-side FAQ: Nosemosis

By Emily Olson, Apiculture Technician, ABC Tech Transfer Program

With arrival of spring, honey bees can safely emerge from their insulated hives to meet the warming sun. Colonies are vulnerable and need plenty of resources to recoup the losses incurred over the winter months. Spring is an important time and high pathogen levels can hinder the progress of the colony. Specifically, Nosema disease is one to consider during this season. Nosema levels are typically highest during the spring and controlling this pathogen is critical to ensuring your colony thrives.

WHAT IS NOSEMA? Nosemosis or Nosema disease is caused by a single celled fungi belonging to the phylum Microsporidia. Nosema reproduce by forming spores which can persist in the environment for many years. There are 2 species of Nosema that infect honey bees: Nosema apis and Nosema ceranae. Recently, these 2 species were reclassified to the genus Varimorpha but are still commonly referred to as Nosema. Originally, Nosema apis was a pest of the European honey bee (EHB) and Nosema ceranae, the Asian honey bee (AHB). However, N. ceranae crossed over to the EHB a few years ago and has become the dominant Nosema species found in our bees. Both species can be found within a single bee but it has been documented that N. ceranae is more detrimental to colonies.

HOW DOES A COLONY BECOME INFECTED WITH NOSEMA? Queens, workers, and drones can become infected with Nosema spores by consuming contaminated food and water, during trophallaxis from an infected to a healthy bee, and by cleaning or robbing contaminated hives. After ingesting a Nosema spore, the fungus will germinate and multiply within the midgut cell, producing more spores and eventually rupturing the cell wall. The spores are released into the midgut and either infect other cells or are excreted. The fecal matter can then contaminate hive substrates (e.g., wax/comb) and infect other bees.

HOW DOES NOSEMA AFFECT HONEY BEES? Nosema infection can cause long lasting digestion issues and lead to a reduced adult bee lifespan. Studies have shown that high number of Nosema spores are associated with malformation of brood-food glands and elevated levels of juvenile hormone. As a result, infected bees often don’t produce brood food and initiate foraging activities prematurely. Younger

bees switch to foraging earlier in life and are therefore less efficient at gathering resources, and less successful at returning to the colony from foraging trips. This results in a shortage of food in the colony, which affects brood rearing and the overall productivity of the hive. Infected colonies are also more susceptible to secondary infections, such as chalkbrood, due to lower brood nest temperatures (a result from the reduced population size) and the damaged midgut cells.

Drones and queens are also susceptible to Nosema disease. Infected drones may have a decreased body mass and sperm viability, reducing the success of mating. Queens with high Nosema spore loads are poor egg layers and there is evidence that oocytes (immature eggs) degrade as a result. Additionally, infected queens are more likely to be superseded, contributing to the poor productivity of the colony.

HOW IS NOSEMA DETECTED? Unfortunately, visual detection is unreliable in diagnosing Nosema disease, as symptoms will often look similar to problems caused by other pathogens or poor environmental conditions. However, closely monitoring your colony is an important step in detecting when something is wrong and should be followed with other diagnoses tools. Greasy looking bees with swollen abdomens and wings held at odd angles can be a sign of Nosema apis infection. If the colony is weak, unproductive, and a reduced population size is noticed, Nosema may be the cause. Dysentery (fecal matter on the outside of the colony) is often associated with Nosema apis but not necessarily the cause. High Nosema infections occur in the spring which coincides with bees leaving the hive after the long winter. Bees do not defecate inside the hive so once the warm spring weather arrives they are free to answer nature’s call. A reliable and accurate method to diagnose Nosema disease is by microscopy. Many beekeepers do this on their own, but samples can also be sent to a lab for testing. • Collect a sample of forager bees from a honey frame (30-60 bees).

• Separate the abdomens, crushed them thoroughly and combine with water (1 mL water per 1 bee abdomen). • Count the spores on 5 squares of the hemocytometer.

• Calculate the number of spores per bee by multiplying the number of spores counted by 50,000. If there are 1 million spores per bee or more, treatment is recommended.

HOW IS NOSEMA CONTROLLED? Once a Nosema infection above the recommended threshold of 1 million spores per bee is identified, colonies can be treated with Fumagillin-B. Fumagillin is an anti-fungal compound and is the only registered chemical treatment for honey bee colonies with Nosema in Canada. It is important to follow the label instructions to ensure the treatment is safe and effective.

Fumagillin suppresses the actively growing stages of Nosema spp. but it has no effect on spores, which can remain dormant on equipment for many years. Fumigation with acetic acid has proven to be effective at killing spores and disinfecting contaminated equipment (for more details, see https:// honeybee.uoguelph.ca/resources-for-beekeepers/aceticacid-fumigation/). Frames can also be sent for irradiation, but this can be time consuming and costly as the closest facility is in Port Coquitlam, BC.

Prevention is always preferable and easier than treating a disease once it takes hold. Ensuring colonies are strong and well fed in the fall will help stave off diseases throughout the winter. Eliminating co-stressors such as other diseases or lack of food/water, reducing weak colonies to a nuc or single box, placing in a warm sunny location, and limiting the amount you go into the hive in the winter/spring will help prevent Nosema disease. The Tech Transfer Program is funded by the Government of Canada and the Government of Alberta through the Canadian Agricultural Partnership.