The tracheal mite, Acarapis woodi, causes what is generally referred too as Acarine disease. The adult mites infest the prothoracic tracheae i.e. the first pair found on the thorax, and complete their life cycle there. They feed on the blood (haemolymph) by piercing with their mouthparts through the tracheal walls.
There is still some controversy about the damage heavy infestation cause, with some bee pathologists claiming serious primary or secondary damage while others dispute this information. It is hard to believe that a bee, whose tracheae are packed with mites that damage the tracheal walls and soil the tracheal interior, is not influenced negatively. It has also been reported that the bees' wing bases and the muscles and nerves of the wings are damaged because the blood and oxygen supply is reduced. The bees are then unable to fly. Secondary infections may also be more prevalent in infested bees whose damaged tracheal walls provide excess for viruses and bacteria into the thorax of the bee.
The mites are tiny and require microscopic examination for undisputed identification. However, heavily infested tracheae can be seen with the naked eye. When the front segment of the thorax of a bee is removed the tracheae are exposed. Healthy tracheae are clear, while infested ones appear brown and may even have black patches of necrotic tissue. Upon examination with a magnifying glass (15 to 20 x magnification) the mites can be seen. Generally it would be advantageous to control mites within a colony. However, this is not as simple as it may seem, because the symptoms are not easily detected, and there is no period or season when mite numbers increase significantly. Infestations have not been correlated with bee race, season, or other environmental factors.
It was generally believed that severely infected bees would loose their ability to fly and crawl out of the hive, but this symptom has been disputed. It has been proven that many infected workers foraged normally. Most bee pathologists agree that the mite is not a serious parasite because it does not cause large-scale bee mortality or any colony losses. But beekeepers may disagree because infested colonies may not produce to their optimum ability, influencing their economic viability.
THE MITE IN SOUTH AFRICA
Trachea mites are found in low numbers in all provinces. Although their numbers apparently increased during winter, the mite population probably remained stable, and the 'increase' can be attributed to the fact that fewer bees are present during the winter.