Beekeepers, currently, do not often discuss tracheal mites, Acarapis woodi, however, this pest species has been detected throughout the Maritimes in the past. Tracheal mites cause a disease known as Acarine disease, or Acariosis, which, with a high infestation, will result in bee mortality throughout the winter, and potentially lead to colony death by spring. Read this week’s blog to learn more about tracheal mites, including the detection and treatment of this pest species.
What Beekeepers Should Know about Tracheal Mites
Tracheal
mites, Acarapis woodi, are a small parasitic mite that infests the
airways (tracheal tubes) of honey bees1. The infestation of honey
bees by the endoparasitic tracheal mite was first associated with a condition
that caused considerable colony mortality in Apis mellifera on the Isle
of Wight, England, in the early 1900s2. The tracheal mite is
approximately 125–175μm in length3 and spends its life in a trachea
of a single host4. Both larval and adult mites pierce the honey
bee’s tracheal walls to feed on their hemolymph5. Mated females will
leave the trachea and migrate to a trachea of a newly emerged bee to start reproducing
and continue the life cycle4.
Given their
relative small size, mites that dwell in tracheal systems of insects are
generally overlooked1. Since the introduction of varroa mites, the
impact of tracheal mites on bees has been largely overshadowed or ignored1.
However, tracheal mites are still present in bees, and may be responsible for
some unexplained colony losses7. There is a need to identify the
presence, and levels, of tracheal mite infestations in Atlantic Canada, given
that this pest species causes Acariosis. High mite infestations will result in
bee mortality throughout the winter, and potentially lead to colony death by
spring1. Damage to bees and colony health are seen when infestation
levels are at 10% or higher.
In the 2016 Canadian
National Bee Health Survey8, tracheal mites were not detected in any
samples from Nova Scotia, Prince Edward Island, or Newfoundland. In 2016,
tracheal mites were detected in 1 of 11 colonies sampled in New Brunswick by
PCR methodology (Polymerase Chain Reaction).
In the 2017
Survey7, tracheal mites were not detected in any samples from Nova
Scotia or Newfoundland. In 2017, tracheal mites were detected in 1 of 8
colonies sampled in New Brunswick, and 1 of 7 colonies sampled in Prince Edward
Island by PCR methodology. There has been no formal study done to assess the
presence of tracheal mites since 2017, but the Atlantic Tech Transfer Team for
Apiculture feels a survey is warranted for our industry and is currently
putting plans in place for research to be conducted in the near future.
There are
some colony indicators of tracheal mite infestation, but confirmation requires microscopic
examination. In cases of severe infestation, large numbers of adult bees crawl
in front of the hive incapable of flying9. Even when the weather is
optimal for flying, a high proportion of bees inside the hive may be another
indication of tracheal mite infestation. Also, colonies are slow to build up
their population in spring, and large numbers of bees will die before that
start of winter9. It is important to remember that colonies show
variability in their sensitivity to tracheal mites, as some populations have
developed a level of resistance9.
To sample for
tracheal mites, approximately 100 older bees are collected and placed in 70%
ethanol. It is best to sample in fall to determine infestation level prior to
entering winter and treat if necessary. There are several methods to detect the
presence of tracheal mites. The tracheal trunk of adult bees can be dissected
and examined for mites under a microscope. Mites are very small but will be
seen as white objects in the trachea1. A second option is to stain
the trachea which will make mites easier to see under the microscope. This is
done by cutting the thoracic disk containing the main trachea and placing the
muscle tissue in 5% potassium hydroxide solution1.
In Canada,
there are two registered products for the treatment of tracheal mites – menthol
and liquid formic acid10.
Treatment is only applied when honey supers are not in place9.
Additionally, beekeepers should test before and after treatment, and always
follow the product label.
References
- Sammataro, D., 2006. An easy dissection technique for finding the tracheal mite, Acarapis woodi (Rennie) (Acari: Tarsonemidae), in honey bees, with video link. International Journal of Acarology, 32(4), pp.339-343.
- Rennie, J., 1921. (4) Isle of Wight Disease in Hive Bees—Acarine Disease: The Organism associated with the Disease—Tarsonemus woodi, n. sp. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 52(4), pp.768-779.
- Delfinado-Baker, M. and Baker, E.W., 1982. Notes on honey bee mites of the genus Acarapis Hirst (Acari: Tarsonemidae). International Journal of Acarology, 8(4), pp.211-226.
- Sammataro, D. and Needham, G.R., 1996. Host-seeking behaviour of tracheal mites (Acari: Tarsonemidae) on honey bees (Hymenoptera: Apidae). Experimental & applied acarology, 20, pp.121-136.
- Pettis, J.S. and Wilson, W.T., 1996. Life history of the honey bee tracheal mite (Acari: Tarsonemidae). Annals of the Entomological Society of America, 89(3), pp.368-374.
- Shakib, V. and Mehdi, E.S., 2016. Unprecedented first record of infestation level Acarapis woodi (Rennie) and overwintering ability in Savojbolagh regions of Alborz province in Iran. J. Entomol. Zoology Stud, 4, pp.1-13.
- Canadian National Honey Bee Health Survey. 2017.
- Canadian National Honey Bee Health Survey. 2016.
- Tracheal mites. 2000. Mid-Atlantic Apicultural Research and Extension Consortium. 4.2.