Nosema is both the name of a condition and the organism which causes it. In the U.S. we have two species, Nosema apis and Nosema ceranae. N. apis has always been with us; however, N. ceranae was recently discovered. After further testing of stored samples of bees, N. ceranae has been in the U.S. since at least 2002.

Both species are a unicellular fungus which resides in the gut of the bee. The parasite has a polar tube which can be likened to a hypodermic needle that can be harpooned. The polar tube penetrates the cells of the bee and then injects the necessary elements for reproduction into the cell. Inside the cell of the bee’s gut, Nosema reproduces by form spores. These spores are then passed with the bee’s waste.

Nosema apis, sometimes referred to as bee dysentery, is most problematic in the winter and spring, and is rarely a problem during the summer. The bees are confined to the hive by the weather and unable to go on a cleansing flight to expel waste. The Nosema aggravates the bee’s gut causing them to expel waste in the hive and on the outside. With bees defecating in the hive, it is likely that other bees will ingest Nosema spores and also become infected. The telltale sign of Nosema apis is the brown spotting on the outside of the hive.

Nosema ceranae can affect a hive at any time of the year. It differs from N. apis in that the bees do not experience the diarrhea and it can cause rapid colony decline. The inability to see symptoms and the organism makes N. ceranae difficult to diagnose.

Both forms of Nosema are treatable with Fumagilin-B. Fumagilin-B is an antibiotic which restricts the “firing” of the polar tube. If the parasite is unable to attach to the cells of the bee’s gut it cannot reproduce. Researches now recommend treating with Fumagilin-B Spring and Fall.