Nosema apis and Nosema ceranae are protozoan parasites of bees and both species are found in Queensland. They are spore-forming organisms grouped within the genus Microspora. Nosema disease affects the intestines of the adult bee.

• The disease
• Diagnosis
• Control

The disease

Nosema is contracted by adult bees ingesting nosema spores in contaminated food or water or through close contact with contaminated colonies such as exposure to infected combs. The spores germinate in the stomach and invade cells along the mid intestine. The organism matures and produces more spores which are released when infected cells rupture. Spores are excreted in the faeces. Dysentery symptoms are commonly accompanied by crawling symptoms in affected bees. Adult bees die off prematurely. Infected nurse bees do not fully develop and infected queens can die suddenly. In extreme cases, scouring can be observed over the front of hives. Generally the hive strength is reduced and likewise hive productivity.

Nosema apis has been recognised in Queensland for many years. More recently, in the light of overseas investigations and new testing procedures, Nosema ceranae has been detected. It has been found all over Queensland and in other states. More investigation into Nosema ceranae infection is being conducted, but at this stage, it is considered the more severe form of the disease. Adult bees can die faster and less dysentery symptoms are observed. An absence of the typical crawling behaviour of affected bees has also been reported.

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Diagnosis

A microscopic examination is the only reliable test for the presence of nosema disease. Thirty to fifty adult suspect bees (sick or only recently dead) or bees collected from the top bars of the frame should placed in a clean jar, preserved with methylated spirits and sent to the laboratory by courier for testing. Testing is conducted at the Biosecurity Sciences Laboratory at Coopers Plains. Nosema species can be detected easily under a 400 magnification microscope. However, differentiation of N. apis from N. ceranae requires a PCR (polymerase chain reaction) test. This test is more expensive and details should be discussed with the laboratory if nosema species identification is required.

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Control

Nosema spores can be found in bees at any time of the year in varying numbers. Most hives have some nosema 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.

Keeping hives dry and protected from extreme conditions such as cool wet winds during the cooler months is necessary. Young queens and timely brood manipulations and hive shifting also aid in stress reduction. It is good practice to leave between three quarters and a full box of honey on hives during autumn for winter stores as poor nutrition frequently leads to nosema disease. Reducing brood manipulation in winter and early spring also helps to keep the spore numbers down. Spring management including replacement of brood combs and providing access to pollen rich flora further reduce the incidence of nosema disease.

Irradiation is used to kill other bee disease pathogens and this will also kill nosema spores. It is illegal to use antibiotics for the treatment of nosema without a special permit from Biosecurity Queensland and honey cannot be produced during treatment as it is contaminated. Heat and fumigation can also be used but this is not a common practice. It is used mostly when heavily contaminated empty frames are identified. Contact a Biosecurity Queensland apiary officer for advice on your particular situation.

The best strategy in managing nosema is to employ good management practices such as placing hives in a warm location, providing access to good nutrition, replacing brood combs regularly and re-queening hives annually.