The oblong mites (Acarapis woodi) are microscopic, averaging 160 microns long by 75 microns wide, about 1.5 times as long as the diameter of a human hair. They live, feed and breed inside the tracheae or breathing tubes of the adult bee. The mite penetrates the tracheal wall with its piercing mouthparts and feeds on bee blood. The effect of feeding, opening the surface to pathogens and the reduced capacity of air flow to the wing muscles are the suspected damaging factors that kill bees.
To determine if bees are infested a sample of bees must be collected and dissected under a microscope. Thirty-five bees are collected away from the brood cluster (below outer cover is a good place) by modified hand vacuum or by shaking and funneling them into a plastic bag. Then bees are frozen until dissections are made.
Dissection Methods
Tracheal “Pull” from Fast-Frozen Bees -
Each bee is placed on it’s back and the head and first pair of legs are removed from the rest of the body with by pulling with two pairs of forceps. One pair (1) holds the bee while the other (2) is used to remove head and legs. Then pair 2 is used to remove the thoracic collar. As the collar is removed, the tracheal tube trunks usually come with them. The mites, if present, can be observed inside the tubes from 10x-40x. This method requires more practice than the next method but does not require soaking over night to clear tissue.
Slice and Soak from bees stored in alcohol -
Each bee is placed on its back, the front legs and head are removed with an edge of a razor blade and a thin cross-section of the prothorax containing the major tracheal trunks is made with the razor blade. The section is soaked overnight in an 8 percent solution of potassium hydroxide in water to dissolve muscle tissue. The tracheae are observed at 20 to 40x under a dissecting microscope for mites. Infested tracheae are usually discolored and darkened in areas where mites have fed.
- John Skinner, University of Tennessee
Bee Informed Partnership