Nosema Disease

If, like me, you thought Nosema was skittery bees – think again because that’s dysentery. Nosema, or should I say Nosemosis, is something else altogether. Read on.

Life Cycle

The proper name for this disease is Nosemosis, Nosema is the name of the creature which causes the disease. Traditionally this was Nosema apis – a single celled fungal parasite which invades and infests the gut of the honey bee. Eventually, it produces reproductive spores, perhaps 100,000 per bee. These spores are quite resistant and persistant and they are voided in the faeces of the bee. If this happens inside the hive, they are picked up by house bees and the cycle repeats.

Like any other creature whose guts are infested with a gut parasite which is eating its food the symptoms are generally draining. In the case of Nosema it is thought that the infection reduces the bees’ capacity to digest pollen which is their source of protein. In turn, the effects of this are to decrease the individual bee’s life by 50% and also reduce the activity of the hypopharyngeal glands and the ability of the bee to produce brood food. These individual effects have implications for the colony as a whole depending on how many bees are infected.


So long as spring build up is accompanied by fair weather, the increasing colony size will outpace the infection and all will be well. On the other hand, if weather be foul and bees are confined to barracks where some indoor voiding may occur then it will spread like wild fire. If this is accompanied by a shortage of pollen, the build up will halt and the colony will be in trouble. Slow spring build up or failure to build up are signs of Nosemosis.

There may also be some voiding of faeces in the hive but if this is extensive it is more likely to be dysentery or stress of some kind. However, dysentery and Nosema may both be present in which case the dysentery will aid the spread of Nosema.

To be sure it is Nosema you need to look at the entrails, open a dead bee and look for softly swollen, whitish guts. Microscopy and experience is needed to confirm this disease.

Recently another species, N.ceranae has been discovered. The symptoms are similar but it is thought to be virulent through the entire year whereas N.apis is a disease of winter/spring. Only microscopic examination by an expert is going to distinguish between the two.

While N.ceranae has been implicated in USA the Colony Collapse Disorder or ‘CCD’ it is only a contributor and not the primary causative agent.

Meanwhile, despite having the potential to become a virulent disease, since being present in Europe since probably 1998 and the cause of a bad dose in Spain in the winter or 2004-5 it seems to be something of a damp squib. Fingers crossed.


The treatment for Nosemosis used to be an antibiotic known as Fumidil B but this is no longer available. Instead, the beekeeper must rely on prevention and good husbandry.

Make sure colonies are strong under young prolific queens. Do not breed from strains which seem prone to Nosema.

Spread can be controlled by routinely fumigating the brood combs of empty hives with acetic acid. Click here for instructions on acetic acid fumigation.

Don’t crush bees. Other bees will come and clean up the mess and if that bee has Nosema – well, away we go again.

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