Nosema apis

Nosema apis is a microsporidian, a small, unicellular parasite that mainly affects honey bees. It causes nosemosis, also called nosema, which is the most widespread of the adult honey bee diseases. The dormant stage of nosema is a long lived spore which is resistant to temperature extremes and dehydration. Nosema apis spores cannot be killed by freezing contaminated comb. Nosemosis is a listed diseases with the Office International des Epizooties (OIE) .

Symptoms

The symptoms may be confused with other diseases of the honeybee. The symptoms include: slow spring buildup, dysentery which is evidenced by yellow streaks on the outside of colony, disjointed wings, distended abdomens, and the absence of the stinging reflex, early supercedure of queens. Bees crawling in front of the hive unable to fly may be infected by nosema but not necessarily so. Longevity is reduced.

Transmission

Newly emerged bees are always free from infection. Spores must be swallowed by a bee for the infection to be initiated. 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 hollow polar filament . Once inside a cell, the vegetative stage increases in size and multiplies, effecting an apparent concurrent 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 normally shed into the ventriculus where they burst - releasing digestive enzymes. When infected cells are shed similarly, they release infective spores when they burst (30-50 million).

Effects on the hive

Nosema spores are spread to other colony members through fecal matter. The disease impairs the digestion of pollen thereby shortening the life of the bee. 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. 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 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 Queens that become infected by the parasite during the brood rearing season are superseded by the bees.

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 brood rearing starts and while flight possibilities are still limited. Colonies in Northern climates are more seriously affected than colonies in the South because of the increased amount of time bees are confined in the hive. Nosema, if left untreated, can cause queen supercedure, winter kills, reduced honey yields and dwindling populations. It is more common during times of confinement like winter and spring.

Diagnosis

Diagnosis is dependent on microscopic examination of the ventricular content and/or fecal 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.

Treatment

Treatment with the antibiotic Fumidil B (prepared from Aspergillus fumigatus, the causative agent of Stone Brood ) inhibits the spores reproducing in the ventriculus, but does not kill the spores. Heat treatment in 49 C for 24 hours can be used to kill the spores.

See also

• Antibiotics
• Diseases of the honeybee
• Honeybee
• Microsporidia

References

• The Hive and the honeybee, Chapter 21 Diseases and enemies of the honey bee T.A. Gochauer, B. Furgala, H. Shimanuki, 1975 published by Dadant
• [1] University of Georgia Honeybee Program
• [2] University of Florida IFAS Extension, Malcolm t. Sanford
• [3] Swedish University of Agricultural Sciences Ingemar Fries, 1993