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Nosema Apis

This page is credited in full to Dave Cushman who created it. His voice is expressed in black colour text and any additions or comments in blue belong to myself.¬†Credit: Dave Cushman’s website.

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Nosema Apis a Parasite of Honey Bees

Nosema apis (Zander) is a microsporidian, it is a small, single celled parasite affecting honey bees. It causes nosemosis, mainly known by the term nosema. Although parasitic, it is often thought of and talked about as a disease. A single spore can cause infection, but the mean infective dose is generally reported to be between 20 and 90 spores per bee.

The dormant spore stage of nosema is resistant to extremes of temperature and dehydration and the spores are long lived.
Symptoms evident

The symptoms can be confused with other honey bee problems, but they are genarally…

dysentery
Shorter life of worker bees
Lack of industry in the colony (slowness of development)
Lower than normal propensity to sting
Crawling bees
Disjointed wings
Distended abdomens
High propensity to supersede

I have included disjointed wings, because many other sources quote this symptom, but I have not recognised this feature myself, maybe the effect is less severe than the ‘K’ wing associated with Acarine infestation.

Bees crawling in front of the hive unable to fly may be infected by nosema but there are other possible causes of this. Crawling bees, trembling wings and dislocated wings are associated with Chronic Bee Paralysis Virus (CBPV).
Transmission and spread

Spores need be ingested by a bee for the infection to be effected. Spores germinate quickly after entering the ventriculus, and the epithelial cells of the ventriculus are infected when the vegetative stage is introduced by way of the extended tubular polar filament allowing inoculation of the sporoplasm into the host cell. Once inside a cell, the vegetative stage increases in size and multiplies, effecting an apparent reduction of RNA synthesis in the host cell. In 6-10 days the infected host epithelial cell becomes filled with new spores. Epithelial cells are shed into the ventriculus where they burst – normally releasing digestive enzymes. The infected cells are shed similarly, but they release 30-50 million infective spores when they burst. With such a rapid amplification of spores, infection is rapidly spread.
Effects on the hive

Queens may become infected from various sources after they emerge from the queen cell. When the disease is severe, colony populations may become depleted and eventually reduce to a handful of bees and a queen. This is often known as “spring dwindling”. Colonies that are only mildly affected can recover.

Nosema spores spread easily to other bees by spores in feaces that are voided inside the hive. The disease disrupts the digestion of pollen and shortens the life of the individual bee. A greater proportion of worker bees become infected than drones or queens, likely because of natural comb cleaning activities of young bees in which drones and queens do not participate. Nosema infected 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 does become infected her ovaries degenerate and her egg laying rate is reduced due to atrophy of the oocytes. Queens that become infected by the parasite during the brood rearing season are likely to be superseded by the bees.

Nosema infection causes earlier worker orientation and commencement of foraging, along with earlier degeneration of hypopharyngeal glands.

There is a seasonal trend to infection, low levels during summer, a small peak during Autumn, and a slow rise of infection during the Winter. In early spring the level of infection increases rapidly when brood rearing starts and flight is limited due to low temperatures. Nosema spores, appearance under microscope
Diagnosis

You can look for the long lived sausage shaped or rice grain shaped spores using a microscope. These spores are 4 to 6?m long and 2 to 4?m wide. They can be seen with a with a magnification between 400x to 1000x (600x prefered). Prepare your sample by macerating 10 or 15 bees under water. Use an opaque medium like Indian (Cuttlefish) ink on the slide to provide contrast.

But nosema can be detected without a microscope… Place your finger nail firmly on the sting and pull the head off exposing the mid gut. The midgut is normally tan and has a distinctive ringed appearance (similar to the segmented body of an earthworm). A midgut that is infected with nosema is off white and is a little swollen and appears slightly less segmented in appearance. This crude field test should be confirmed by microscopy if nosema is suspected to be present.
Treatment

There are two schools of thought on this… My personal preference is not to treat and thus lose the susceptible bees from my collection of stock. This helps to weed out genetic weakness and promotes bees that are capable of withstanding the conditions that they are expected to work in.

Treatment can be given using the antibiotic Fumidil ‘B’ which is prepared from Aspergillus fumigatus, which is the causative agent of Stone Brood. Fumidil ‘B’ inhibits the reproduction of spores, but the antibiotic does not kill the spores themselves. Heat treatment of infected equipment, at 49

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