From an Ibra reprint (1993) by Ingemar Fries at the at the Department of Entomology,
Swedish University of Agricultural Sciences


Effects from Nosema apis on Apis mellifera

On colony level	On individual level
-increased winter mortality	-reduced lifespan
-reduced honey yield	-faster physiological ageing
-poor spring buildup	-atrophy of hypopharayngeal glands
	-supersedure of infected queens
	-aggrevates dysenterea

The traces of Nosema can best be seen in the
spring when bees are old and weak after winter.
Here are the feaces on top of frames. The bees
could not get out to deficate during winter. When
the bees try to clean it up more individuals will be
infected by the spores.

The Nosema spores enters the honey bee through the food canal, and they germinate under the influence of the gut juices.

Diagnosis

Diagnosis is dependent on microscopic examination of the ventricular content and/or feacal matter. No specific outward sign of disease is present, although in dissections the ventriculus often appears whitish and swollen in a late stage of infection. The disease is easily detected in samples of whole bees macerated in water. The fluid is examined under light microscope at 250-500 x magnification where the characteristic Nosema spores can be observed.

Nosema spores together with a pollen grain.

The life cycle of Nosema. Click on picture for a larger (40k) version.

The level of infection found in a colony is highly variable. The seasonal trend of typical infections exhibits low levels during summer, a small peak in autumn, and a slow rise of infection during winter. In the spring the level of infection increases rapidly as beood rearing starts and while flight possibilities are still limited.

Newly emerged bees are always free from infection. Flight bees collected at the entrance are more infected than house bees. Infected bees has a tendency to congregate in the warmer parts of the hive.

All adult honey bees are susceptible to Nosema. A greater proportion of worker bees become infected than drones or queens, probably due to the comb cleaning activities of young bees in which drones and queens do not participate. Nosemainfected bees do not attend or feed the queen to the same extent as healthy bees, which helps the queen to escape infection. When the queen becomes infected her ovaries degenerate and her egg laying capacity is reduced due to atrophy of the oocytes. Queens that become infected by the parasite during the brood rearing season are superseded by the bees.

Nosema infections are frequently present in most apiaries without causing significant damage. It is aggravated by stress. Colony disturbance in winter as well as during summer increase the risk of detectable disease level.

Addition of protein to the bees promotes the development of Nosema in cage experiments suggesting that supplementary feeding with protein in the spring should be done with caution. However, managing colonies to avoid protein deficiency has also been shown to be beneficial. Supplementary feeding of protein or moving to areas with a good supply of pollen reduces the infection level in infected colonies, probably due to a larger number of bees being produced.

Disease prevention

Nosema disease can be transmitted with wax. Colonies transferred in early summer to wax contaminated with Nosema spores often develop Nosema disease the following spring. To prevent disease outbreak, bees can be transferred to non-contaminated equipment early in the season. However, good results in cold climates have also been demonstrated by wintering bees only on foundation. Reports from middle-Europe on foundation wintering is less favourable.

Robbing of honey from weak colonies spreads the disease since the stores of heavily infected colonies often contains spores. Other factors that contribute to the spread of Nosema spores within the bee colony include management where bees are crushed. The liquid remains of crushed bees are readily ingested by other bees.

To reduce the need for changing and melting combs, acetic acid fumigation of combs has been used to kill Nosema spores. Ethylene oxide has also been found effective in decontaminating equipment. Heat treatment in 49 C for 24 hours can be used to kill the spores, and so can gamma radiation.

A simple way to make combs free from viable Nosema spores is to use acetic acid. A 60% solution can be used for this purpose, with approximately 2 ml per litre volume to be treated. The acid is put on top of a stack of boxes in an empty box that is closed with a lid. The acid is allowed to remain in an open container on the combs until it has evaporated or until the combs are to be used again.

The antibiotic Fumagillin kills the active stages of Nosema, but not the spores, and it's effect diminish over time. Experiments show that even when fumagillin is administered both in the autumn and spring, infection levels might still be harmful. Wintering bees on clean or disinfected combs are therefor advisable with or without medication.