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.

Microscopic view of Acarapis woodi ©Shakib and Mehdi, 2016⁽⁶⁾

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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. Canadian National Honey Bee Health Survey. 2017.
8. Canadian National Honey Bee Health Survey. 2016.
9. Tracheal mites. 2000. Mid-Atlantic Apicultural Research and Extension Consortium. 4.2.

In Atlantic Canada, commercially managed bees, such as honey bees, are the main insects used for pollination, but native bees also play an important role in wild blueberry pollination. Some of the native pollinators involved in pollination include bumble bees, andrenid bees, halictid bees and mason bees⁽¹⁾. Bumble bees (genus Bombus) use floral sonication or buzz pollination while foraging, which involves vibrating the flower to allow pollen to be released from the anthers. Wild blueberries have coevolved with bumble bees to allow the release of pollen using this method⁽²⁾. Given the symbiotic relationship bumble bees have with wild blueberries, and their suitability for Atlantic Canada’s climate, bumble bees are very efficient pollinators in the Maritimes. Read this week’s blog to learn about the multiple species of wild bumble bees that contribute to blueberry pollination in the Maritimes, and key features to identify them.

Get to Know Your Bumble Bees

Eastern Canada has a large diversity of bumble bees, with over 18 known species found in our region, and over 40 species found throughout Canada. That being said, some are found foraging around blueberry fields in Atlantic Canada more often than others, and those are the species being highlighted with the information provided.

Bombus impatiens, the common eastern bumble bee, is the most encountered bumble bee across eastern Canada. The species is highly adaptable and can live in country, suburbs, and urban cities³. Their adaptability makes them a great pollinator species, leading to an increase in their commercial use. When identifying the common eastern bumble bee, queens have bigger bodies measuring 17–23 mm. Workers have bodies that are 8.5–16 mm, and males have bodies that are 12–18 mm⁽³⁾. Queens and workers are both black with a yellow thorax and yellow first abdominal segment. Drones slightly differ in their coloring, where they have a yellow face and head⁽⁴⁾.

Bombus impatiens ©ATTTA (2023)

Bombus ternarius, commonly known as the orange-belted bumble bee or tricolored bumblebee, is a yellow, orange, and black bumble bee. The species is also common throughout eastern Canada⁽⁵⁾. Bombus ternarius is a small, fairly slender bumble bee. The queen is 17–19 mm long. The workers are 8–13 mm, and drones are 9.5–13 mm in length. The queens and the workers have black heads, with a few pale-yellow hairs. The anterior and posterior thorax and the first and forth abdominal segments are yellow. Abdominal segments 2 and 3 are orange, and the terminal segments are black^(6,7). The drone has a yellow head with a few black hairs^(6,7).

Bombus ternarius ©ATTTA (2023)

Bombus bimaculatus, the two-spotted bumble bee, can be found throughout Atlantic Canada. The bee's common name comes from the two yellow spots on its abdomen⁽⁸⁾. Queens and workers have a black face with a triangular patch of yellow hairs on the vertex. Their thorax is yellow except for a shining area on the disc that is bordered by black hairs⁽⁹⁾.  Drone faces have intermixed black and yellow hairs⁽⁹⁾.

Bombus bimaculatus ©Sheffield and Palmier (2023)

Bombus vagans, the half-black bumble bee, is a small bumblebee with a wide distribution in North America⁽¹⁰⁾, and present throughout eastern Canada. The head, thorax and first two segments of the abdomen are yellow while the rest of the abdomen is black, hence the name “half-black”⁽¹¹⁾. The face has a mixture of yellow and black hairs, and the thorax is covered in shaggy yellow hair except for a smooth central portion which is bare and shiny⁽¹¹⁾.

Bombus vagans ©Koch et al. (2012)

Bombus rufocinctus, the red-belted bumble bee, is another species found in Atlantic Canada. The queen is 16–18 mm long. She is black with scattered gray and yellowish hairs on the head. Her abdomen has many bright yellow hairs and areas of reddish hairs⁽¹²⁾. The worker is 11–12 mm long. She is similar to the queen, but she may have longer hair. The male is 12–13 mm long. He is mostly black with more yellow on the head and abdomen⁽¹²⁾.

Bombus rufocinctus ©Ron Payne (Idaho Official Government Website)

A final species to mention is Bombus terricola, the yellow-banded bumblebee, which is native to southern Canada. It was at one time a common species but has declined in numbers since the late 1990s⁽¹³⁾. The Xerces Society for Insect Conservation has placed Bombus terricola on their "Red List" of endangered bees. The yellow-banded bumblebee is black and yellow and has a characteristic fringe of short yellow-brown hairs on its fifth abdominal segment⁽¹³⁾. The queen is about 18 mm long. The worker is similar in appearance to the queen but smaller at a length of 9–14 mm⁽¹³⁾. The male is intermediate in size, being 13–17 mm long⁽¹³⁾.

Bombus terricola ©COSEWIC (2015)

It is important to remember the role native pollinators have when it comes to wild blueberry pollination. The background pollination provided by bumble bees and other native pollinators is not insignificant, so, as an industry, there are important steps and considerations for protecting these native pollinators that, in turn, will benefit the industry.

References

1. Sheffield, C.S., Kevan, P.G. and Smith, R.F., 2003. Bee species of Nova Scotia, Canada, with new records and notes on bionomics and floral relations (Hymenoptera: Apoidea). Journal of the Kansas Entomological Society, pp.357-384.
2. De Luca, P.A. and Vallejo-Marín, M., 2013. What's the ‘buzz’ about? The ecology and evolutionary significance of buzz-pollination. Current opinion in plant biology, 16(4), pp.429-435.
3. Williams, P.H., Thorp, R.W., Richardson, L.L. and Colla, S.R., 2014. Bumble bees of North America: an identification guide (Vol. 89). Princeton University Press.
4. Plath, O.E., 1934. Bumblebees and their ways. Bumblebees and their Ways.
5. Eaton, E.R. and Kaufman, K., 2007. Kaufman field guide to insects of North America. Houghton Mifflin Harcourt.
6. Richards, O.W., 1946, September. Observations on Bombus agrorum (Fabricius)(Hymen., Bomhidae). In Proceedings of the Royal Entomological Society of London. Series A, General Entomology (Vol. 21, No. 7‐9, pp. 66-71). Oxford, UK: Blackwell Publishing Ltd.
7. Cumber, R.A., 1949. The biology of humble-bees, with special reference to the production of the worker caste. The Royal Entomological Society of London.
8. Devore, B. 2009. Pollinators. Department of Natural Resources: 12.
9. Medler, J.T. and Carney, D.W., 1963. Bumblebees of Wisconsin.
10. Hatfield, R., Colla, S., Jepsen, S., Richardson, L.L., Thorp, R.W. and Jordan, S.F., 2014. IUCN Assessments for North American Bombus spp. for the North American IUCN Bumble Bee Specialist Group. The Xerces Society for Invertebrate Conservation. Available online: https://xerces. org/sites/default/files/publications/14-065. pdf (accessed on 18 August 2020).
11. Colla, S., Richardson, L. and Williams, P., 2011. Bumble bees of the eastern United States. USDA Pollinator Partnership.
12. Owen, R.E. and Plowright, R.C., 1988. Inheritance of metasomal pile colour variation in the bumble bee Bombus rufocinctus Cresson (Hymenoptera: Apidae). Canadian journal of zoology, 66(5), pp.1172-1178.
13. Hatfield, R.G. and Jepsen, S.A.R.I.N.A., 2021. A conservation conundrum: protecting bumble bees under the California Endangered Species Act. California Fish Wildlife J, 107, pp.98-106.

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca