Bee Tracheal Mite - Acarapis woodi
The honey bee tracheal mite, Acarapis woodi, or acariosis as the
disease is known in Europe, afflicts only adult honey bees. The parasite
was first described in 1921 in bees in Great Britain. This discovery and
concern over the potential impact that this mite would have on beekeeping
in the United States led to the enactment of the Honeybee Act of 1922,
which restricted the importation of honey bees from countries where this
mite was known to exist.
There are three Acarapis species associated with adult honey bees: A.
woodi, A. externus, and A. dorsalis. These mites are
difficult to detect and differentiate due to their small size and
similarity; therefore, they are frequently identified by location on the
bee instead of morphological characteristics. However, only A. woodi
can be positively diagnosed solely on habitat; the position of other
species on the host is useful, but not infallible. Acarapis woodi
lives exclusively in the prothoracic tracheae; A. externus, being
external, inhabits the membranous area between the posterior region of the
head and thorax or the ventral neck region and the posterior tentorial
pits; and A. dorsalis is usually found in the dorsal groove between
the mesoscutum and mesocutellum and the wing bases.
The A. woodi female is 143-174 um in length and the male 125-
136 um. The body is oval, widest between the second and third pair of
legs, and is whitish or pearly white with shining, smooth cuticle; a few
long hairs are present on the body and legs. It has an elongate, beak-like
gnathosoma with long, blade-like styles (mouthparts) for feeding.
When over 30 percent of the bees in a colony become parasitized by A.woodi,
honey production may be reduced and the likelihood of winter survival
decreases with a corresponding increase in infestation. Individual bees
are believed to die because of the disruption to respiration due to the
mites clogging the tracheae, the damage caused by the mites to the
integrity of the tracheae, microorganisms entering the hemolymph (blood)
through the damaged tracheae, and from the loss of hemolymph.
The tracheal mite has now been reported on every continent except
Australia. Initial detectionís of A. woodi were reported in
Brazil in 1974, in Mexico in 1980, and in Texas in 1984. The mites are
transmitted bee to bee within a colony by queens, drones and workers. In
addition, the movement of package bees and queens, as well as established
colonies, has resulted in the dissemination of this mite throughout much
of the United States.
One of the first problems that became apparent when the tracheal mite
was detected in the United States was the lack of agreement on their
economic impact. The literature from Europe did not always agree and
beekeepers, research scientists and regulatory officials had differing
opinions on the interpretation of the data. However, it soon became
evident that the mites were having a serious impact on beekeeping and
spreading faster than one would have ever predicted. The level of
infestation within colonies was higher than expected. It is apparent that
the tracheal mite found an extremely susceptible honey bee host in the
The population of A. woodi in a colony may vary seasonally.
During the period of maximum bee population, the percentage of bees with
mites is reduced. The likelihood of detecting tracheal mites is highest in
the fall and winter. No one symptom characterizes this disease; an
affected bee could have disjointed wings and be unable to fly, or have a
distended abdomen, or both. Absence of these symptoms does not necessarily
imply freedom from mites. Positive diagnosis can only be made by
microscopic examination of the tracheae; since only A. woodi is
found in the bee tracheae, this is an important diagnostic feature.
In sampling for A. woodi, collect moribund bees that may be
crawling near the hive entrance or bees at the entrance as they are
leaving or returning to the hive. These bees should be placed in 70% ethyl
or methyl alcohol as they are collected. Bees that have been dead for an
indeterminate period are less than ideal for tracheal mite diagnosis.
Menthol is the only material that is currently approved by the
Environmental Protection Agency (EPA) for the control of these mites in
the United States. Beekeepers can minimize the impact of tracheal mites by
intensive management practices to maintain populous colonies and by using
Colonies can be treated with menthol when there is no heavy nectar flow
and daytime temperatures are expected to reach at least 60 F. The best
time being in the spring when the weather is warm, and in the late summer
or fall of the year immediately after removing the surplus honey.
Directions for Using Menthol: Fifty grams (1.8 ounce) of
crystalline menthol should be enclosed in a 7" x 7" plastic
screen bag or equally porous material and placed inside a colony for 20-25
days. Menthol placed on the top bars is the preferred method of treatment
provided the daytime temperature does not exceed 80 degrees F. During hot
weather, the menthol should be placed on the bottom board of the colony.
There should be no honey supers on the hive during the treatment, and the
menthol should be taken out of a colony at least one month before any
anticipated flow. Before using menthol, read and follow the approved label