It is a contagious endoparasitosis, which invades the respiratory tract of adult bees, located in the first pair of trachea, which can cause death of the infested colony.
Acarapisose, discovered in Britain, was mistaken for the disease on the Isle of Wight until 1921, the year Rennie needed its etiology.
The disease was diagnosed on the European continent in the 1920s, in Belgium, France, Switzerland, Austria and Poland, as well as in Germany and Spain, always causing a high mortality in bee colonies. Today it is expanding all over the world except Australia.
Several stages of life of Acarapis woodi from the tube of the trachea of the bee (larva, male, female, egg).
The causal parasite of Acarapisose is also called Tarsonemus woodi, which was replaced by the current Acarapis woodi, by Hirst.
Acarapis woodi belongs to the type Artropoda, class Arachnida, order Acarina, family Tarsonemidae and is specific honey bee parasite. There is sexual dimorphism, so the male (85-116mm x 57-85mm) is smaller than the female (80mm x 120mm). The male has the broadest legs, presented in the dorsal part of its body, three segments, while the female has five segments.
They have olfactory hairs that are found in the ends of the first two pairs of paws, and in the male, also in the fourth pair, being more developed in this one for the search of the females. For the insulation they mainly use the second and third pair of legs. It has a slightly yellowish brown color and a picador buccal apparatus.
Hosts: receptivity factors
Acarapisis affects the adult bees of the colony and the Acarapis woodi parasites of the same form the queen, the workers and the drones. The mite installs almost exclusively on the first pair of thoracic tracheas, which are larger than the rest, which allows the parasite to penetrate.
The age of the host plays a major role in the receptivity of the mite. The bees are free of this parasite when they are born, but they are not the most receptive, since they have contact with the old and infected bees, being able to be affected up to 90% of the cases, reducing this percentage to 10%, when the host reaches the age of five days. This is due to the barrier of the bee’s hair, which surrounds the stigmas of the thorax, which thickens and hardens, which allows the parasite to escape, but not the entrance.
Relationship: Parasite / Host / Environment
Acarapis woodi female Acarapisose is a disease whose parasite depends on many ecological factors. It is endemic in certain regions and in others it occurs sporadically.
The female of A. woodi fertilized penetrates the trachea of the bee and at 4-5 days performs the posture, which is not very abundant, 5-6 eggs. These eggs hatch at 4 days, resulting in bag-shaped larvae and only with the first pair of paws developed, consume the host’s hemolymph and after 6-7 days, they become deutoninfas with four pairs of legs, which later give rise to adult mites.
The total duration of development of the mite from hatching to adult mite formation is 11-12 days for males and 13-16 days for females. These, once fertilized, leave the trachea soon after and by contact, pass to the system of the trachea of the other bee. The scarcity of food or poor weather inside the hive increases the chances of spreading the disease.
It is often a certain period of latency of the disease, since the rate of multiplication of the mite in the bee colonies is low. In the summer many infested bees die and, therefore, the pressure decreases.
Good weather and abundant flowering mean that the risk of this parasite is not appreciated on many occasions, since it produces a spontaneous regression of the disease, which is due to the low reproduction rate of the mite and the relatively short life of the bees (30-40) days. In winter, when bees live longer, mites can best exert their pathogenic action.
The mite supports with more difficulty the low temperatures than the high ones, because at 15ºC, its movements are slow, being normal at 30-34ºC. The low ambient humidity damages and the high favors its development.
The odor of bees does not influence the orientation of the mite in the search of the host and can live a short time in the dead bees (12-15 hours), as it happens outside the mites, since it needs to feed. The average life of a mite is 15-20 days, although most die after 10 days. The transmission of the disease in an apiary takes place through drift, pillage and handling errors of the beekeeper; between distant apiaries, uncontrolled transhumance, and commercial transactions.
Acarapis woodi, inside the first pair of thoracic tracheas, produces a mechanical obstruction in the airways, preventing the arrival of oxygen to important muscle zones and nerve centers.
The parasites rupture the tissues of the trachea, which allows the entry of bacteria and viruses, using its powerful oral device and consume the hemolymph that circulates through the muscular masses that surround the trachea, depositing toxins in it.
The first pair of thoracic tracheas is at the height of the joint of the wings. Underneath this joint there is a complex neuromuscular system, which is affected by the parasite.
The symptomatology of the disease is neither precise nor characteristic. When they manifest symptoms, the bee continues its work in a habitual way. The parasitosis can have a long period of latency, 2-3 months, in which there are no symptoms. When the disease worsens, the flight of the bees is slow and sometimes impossible by changing the muscles of the wings, which appear tremulous. These have an abnormal position, perpendicular to the body and falls, such as displaced. They make great efforts to start the flight. Bees gather in small groups before dying. The abdomen appears distended, due to the impossibility of carrying out the cleaning flight, during mild days.
The disease can remain throughout the winter in the colony. Premature consumption of body reserves causes excessive repletion of the rectal blister of parasitized bees, which have a dilated abdomen, which can result in dysentery.
Avoid the drift, pillage and handling errors of the beekeeper, as the most appropriate means to spread the disease. The beekeeper facilitates the fight against this disease when working with vigorous colonies and young queens with great posture potential.