Roe Valley Beekeepers Association
This is an endemic minor pest of bees. It can turn into a major debilitating illness when the colony is stressed. It is a single celled organism that lives on the lining of the gut of the bee, reducing its ability to digest food properly. It is spread through the faeces. Normally the bee defecates away from the hive, taking the nosema spores with it. Under stress conditions, eg dysentry, the bee may defecate in the hive. It will be cleaned up by other bees thus perpetuating the disease.
Every hive will have some nosema. If the beekeeper carelessly squashes a bee when manipulating boxes the only tools the other bees have with which to clean up the mess, including gut contents, is their mouthparts. This helps spread the spores.
The beekeeper can best keep Nosema at an unnoticeable level by being careful not to squash bees by not stressing them unnecessarily, and by frequently renewing their comb.
Nosema ceranae is an emergent pathogen of western honeybees. It is similar to the endemic species, Nosema apis. Both are spore-forming intracellular microsporidian parasites. Adult bees are infected by ingesting spores, which germinate in the gut and infect the ventricular cells. The ability of bees to absorb nutrition, particularly protein, is impaired. Nosema ceranae was originally described in 1996 as the ‘Asian variant’ of N. apis affecting the eastern honeybee. Nosema ceranae is considered to produce a more virulent disease than N. apis, probably reflecting its more recent association with the western honeybee. Nosema ceranae symptoms differ from those produced by N. apis. The dysentery and crawling behaviour associated with the latter infection may not be displayed by bees infected with N. ceranae. Rather the symptoms of an infection are more nondescript and include colony dwindling and increased overwintering mortality. Management of N. ceranae is currently the same as for N. apis. At the present time, approximately 20% of beekeepers in Northern Ireland treat for Nosema using mainly the antibiotic fumagillin dicyclohexylammonium (trade name Fumidil-B). Experimental studies have shown that this treatment is effective against N. ceranae, although work is ongoing. Antibiotics, though, will not kill spores in the hive, so comb changing and a hive scorch are recommended to clear an infection. As with all bee diseases, hygiene, good nutrition and vigilance are paramount.