Nosema is the most common and widespread, serious bee disease directly affecting adult honeybees, including queen bees. In some years it may cause serious losses of bee colonies in autumn and spring.
Nosema spores can be found in bees at any time of the year in varying numbers. Most hives have some spore numbers, but clinical signs and adverse effects only occur when the hive is stressed. Then spore numbers escalate quickly resulting in dead bees, a restless, weak colony and dysentery stains on the hive floor, entrance and walls.
Fortunately, serious nosema outbreaks do not occur every year. In these epidemics, strong colonies may be seriously weakened before winter. They may be reduced to the size of a nucleus colony in a matter of days.
Infected colonies that survive the winter may require a long build-up period for the population of adult bees to reach normal numbers.
Two types of Nosema are known: Nosema Apis and Nosema Ceranae. The latter is the more serious bee disease and can wipe out entire bee colonies within a short time.
The two types of Nosema are being researched and results published. It gets complex and confusing trying to find conclusive answers; some symptoms might appear or not, or it is uncertain whether they are the symptoms of one or the other type, or both in conjunction.
Dysentery stains found inside or outside the hive are actually an indication that the bees are under extreme stress and not necessarily proof of Nosema.
However, without the signs of any other diseases present the assumption can be made with great certainty.
Examination of adult bees in a laboratory is the only reliable method of diagnosing the presence of spores of nosema.
Defecation in the hive and signs of unusual faeces on the outside of the hive is the most common indication of the disease present.
Unusual faeces on the outside of the hive is the most common indication of Nosema.
Combs covered with brown freckles are another indication.