F38 <Nosema>
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About Nosema Disease


Nosema apis spores x 400 magnification

Nosema is a unicellular parasite of the class of microsporidian that develops and multiplies in the cells of the epithelium in the mid-gut of adult bees. Nosema is spread by transfer of spores during trophallaxis or when young bees clean up faecal material on contaminated combs. (Williams et al. 2008). Young queens that ingest Nosema spores normally are superseded within a month (Mussen, 2002).There are two described species for honeybees, Nosema apis and Nosema ceranae and spores of both species can persist in the hive.

The micro-organisms responsible

Nosema apis reduces the lifespan of infected bees, increases winter mortality and causes poor spring build-up. There are no specific symptoms but the disease is linked with dysentery (visible on brood comb and around the hive entrance), disjointed wings and crawling bees outside the hive. Colonies that survive through to summer recover as the bees defaecate outside the hive and infected bees die without transmitting their infection. Spores of Nosema apis can withstand temperature extremes and dehydration. The spores persist on contaminated comb and may trigger a more severe infection the following winter (Bailey, 1981).

Nosema ceranae has crossed the species barrier from its Asiatic host, Apis cerana, and does not display the symptoms associated with N. apis. N. ceranae has been found to be more virulent than N. apis and although numbers of spores build up more slowly they go on to reach higher levels and resulted in higher mortality in cage experiments (Paxton et al, 2007). Infected foraging bees die away from the hive and this continuous loss of bees reduces food brought in to the hive until the colony collapses. N. ceranae can also be spread when foragers add nectar from their infected crops to the pollen they collect. Feeding larvae with contaminated pollen prevents the removal of infection during the summer.

What needs to be done?

Diagnosis
Nosema diagnosis can be carried out using a microscope with X 400 magnification. Collect about 30 bees and mash the abdomens in a pestle and mortar with a few drops of water. Deliver a single drop of the resulting soup onto a microscope slide and put on a cover. Under the microscope look for little pale rice shaped grains that are Nosema spores. There is little difference to be seen between N. apis and N. ceranae spores, if you need to know send a sample to the NBU for analysis (see link below).

Treatment
Fumidil B is an antibiotic for use against Nosema and is successful at temporarily reducing this parasite (Williams et al. 2008)

Treatment methods

In Autumn feed: -
Each colony should receive 166mg of Fumagillin in the autumn feed. A small pack of Fumidil B represents 0.5gm of Fumagillin (25gm of soluble powder) and will treat 3 colonies.
1. Heat 7 pints of water per colony to 38° C (DO NOT EXCEED 49°C)
2. Add one third of the small pack for each colony and dissolve.
3. While water is still hot add 6.35kg (14lbs) of sugar per colony and stir to make clear syrup.
4. Feed the syrup to the bees in the usual way. (Rothamstead).

Spring treatment for small colonies: -
1. Dissolve a small (25gm) pack of Fumidil B in 12 litres of strong sugar syrup and syringe 50ml to 100ml of warm syrup over the top bars and bee ways near the cluster to encourage the bees to clear it up.
2. Repeat 3 to 5 times at two-day intervals then feed remaining syrup in a contact feeder.
3. A feed supplement such as Vitafeedgold used in a similar manner will be beneficial, (follow the instructions on the pack).

Caution. Use protective equipment when handling Fumidil B. Prepared Fumidil B is viable for only 2 weeks.

Reducing infection levels

Making a Bailey frame change or Shook Swarm into a clean (scorched) hive will reduce spore counts. Supers and brood frames can be fumigated with 80% acetic acid. Stack supers as tightly sealed as possible with an acetic acid pad over every two supers, protect metal parts with Vaseline and leave for a week to 10 days. Air frames well before use.


Nosema ceranae spores x 400 magnification

 

 

 

Prepared from NBU (CSL/National Bee Unit)
Fact sheet no 15 by John Verran (RBI for Wales)

For more information go to the National Bee Unit pages of CSL website

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