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About Nosema

Nosema apis and N. ceranae are microsporidian fungi that infect the gut of honey bees causing dysentery, crawling behavior, disjointed wings, and loss of sting reflex. This parasitic fungi infects adult bees, primarily affecting workers. At high infection levels it can also affect young nurse bees, and even the queen. Nosema is spread through feces, and by mouth to mouth transmission.  Previously, N. apis was the predominate strain affecting the honey bee in the U.S. We know now that N. ceranae has displaced N. apis, and is the most virulent strain affecting the honey bee. Nosema is more challenging in the northern U.S. and Canada because the bees are confined in the hive during the winter months.

Hives acutely infected with N. ceranae exhibit cessation of feeding behavior and non-stop brood rearing in winter.  Dysentery is common in northern areas but not reported in southern climates.  Packages and nucs do not build in the summer.  They appear to “stand still” at 4-6 frames of bees/brood.  N. ceranae can kill bees in 8 days and colony depopulation/collapse may be rapid.  Infection of N. cerenae suppresses the immune response of honey bees.  N.ceranae infection has been found in workers, queens, drones and larvae.  It has been detected in tissues and body parts of bees in addition to the gut.

Diagnose Your Colonies

The only reliable test to diagnose Nosema is through microscopic examination. If you suspect your bees have Nosema, or if you plan to take prophylactic measures for Nosema, we recommend you connect with your local diagnostic expert to have your bees analyzed.

Submission of your honey bees to the diagnostic network is confidential, and test results from your colonies will not be made public. We do collect data on Nosema infection level and trends throughout the state; this data does not indicate the hive or individual submitting the sample. We use this valuable data to make better, more informed management decisions on beekeeping in New Hampshire.


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