Nosema disease

Nosema apis and Nosema ceranae are single-celled parasites of bees. They are spore-forming, fungi-related organisms grouped within the class Microsporidia.

Both species are found in Queensland.

Nosema apis has been recognised in Queensland for many years.

Nosema ceranae has been found all over Queensland and in other states.

Nosema is contracted either by:

• adult bees ingesting nosema spores in contaminated food or water
• 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.
• infected queens can die suddenly.
• In extreme cases, scouring can be observed over the front of hives.

Generally, hive strength and productivity are reduced.

Nosema ceranae infection is considered the more severe form of the disease. Adult bees can die faster and less dysentery symptoms are observed. The typical crawling behaviour of affected bees may also be absent.

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
• dysentery stains on the hive floor, entrance and walls.

Prevention

• Keep hives dry and protected from extreme conditions such as cool wet winds during the cooler months.
• Reduce stress through young queens, timely brood manipulations and hive shifting.
• Leave between ³/₄ and a full box of honey on hives during autumn for winter stores as poor nutrition frequently leads to nosema disease.
• Reduce brood manipulation in winter and early spring to help keep the spore numbers down.
• Replace brood combs.
• Provide access to pollen rich flora.

A microscopic examination is the only reliable test for the presence of nosema disease. Nosema species can be detected easily under a 400x magnification microscope. You can send samples to the Biosecurity Sciences Laboratory to determine whether your hives are infected with nosema.

You need a PCR (polymerase chain reaction) test to differentiate N. apis from N. ceranae. This test is more expensive, and you should discuss details with the laboratory if you need to identify nosema species.

Irradiation will kill nosema spores.

There are no chemical treatments for nosema permitted for use in Australia.

You can use heat sterilisation on boxes and equipment, if you have identified heavily contaminated empty frames.

The best strategy in managing nosema is using good management practices to maintain strong healthy hives and removing possible causes of stress such as:

• placing hives in a warm location,
• providing access to good nutrition
• replacing brood combs regularly
• re-queening hives annually.