Small, oval mite (note the eight legs) seen on the body of a pupa inside a cappedcapping:
the covering that bees add over comb cells containing fully ripened honey or to cap brood that has reached the pupal stage; bee bread cells are not capped
cell, or on an adult bee body. When feeding under abdominal segments of an adult bee only a small sliver of mite is visible. Feeding or reproduction of mites on honey leading to premature aging of adult bees. Feeding by mites resulting in transmission or enhanced replication of virus diseases that may reach epidemic proportions. causing elevated levels of fall or colony overwinter death.
Varroa mites (specifically Varroa destructor) are a common parasite found nearly everywhere honey bees are found. Varroa destructor was likely first introduced to western honey bee (Apis mellifera) colonies around 1950, when humans first carried A. mellifera to the native range of the eastern honey bee (Apis cerana), the natural host of Varroa destructor. A similar species, Varroa jacobsoni, is a relatively benign parasite of eastern honey bee colonies, causing little damage, but Varroa destructor is considered the most serious pest of western honey bee colonies and one of the primary causes of honey bee decline. A western honey bee colony infested with Varroa destructor that is not managed or treated will likely die within one to three years. Every beekeeper should assume their colonies have a varroa mite infestation.
Varroa mites attack honey bee colonies as an external parasite of adult and developing bees, feeding on adult fat bodies and hemolymphhemolymph:
the insect equivalent of mammalian blood
. There are two phases of varroa mite parasitism: phoretic (dispersal) and reproductive. In the phoretic stage, female mites seek transport to a brood cell about to be cappedcapping:
the covering that bees add over comb cells containing fully ripened honey or to cap brood that has reached the pupal stage; bee bread cells are not capped. This will usually result in mites changing adult bee hosts. The adult female mites feed on adult bee body fat through the softer exoskeletons of adult bees, primarily between the bee's lower abdominal body segments. This enables mite egg maturation. During the reproductive phase, varroa mites are enclosed within cappedcapping:
the covering that bees add over comb cells containing fully ripened honey or to cap brood that has reached the pupal stage; bee bread cells are not capped cells where the female mite initially produces a male egg and thereafter female eggs. The founding female opens a feeding site in the pupal bee’s exoskeletonexoskeleton:
external body covering (skeleton) of insects
for her nourishment and that of her developing offspring.
For Varroa destructor on western honey bee hosts, the cappingcapping:
the covering that bees add over comb cells containing fully ripened honey or to cap brood that has reached the pupal stage; bee bread cells are not capped stage of workers is sufficiently long enough to enable the foundress female to reproduce one male and at least one female offspring to maturity. Brother and sister male and female mites mate prior to adult bee emergence. On drone brood of the western honey bee, Varroa destructor females will produce two to three offspring (on average), whereas in the eastern honey bee, only invasion of drone brood cells allows Varroa jacobsoni to reproduce.
There are several options for control of varroa mites. The best approach is to keep mite numbers low in a colony. This is described as flattening the mite growth curve in the spring. A multi-faceted approach to control is best described as integrated mite management (IPM). With IPM, monitoring and correct pest identification help you to treat only when needed. IPM includes:
Cultural control - seeks to reduce mite population buildup
Genetic control
Using hygienic bees, for example, or a selected bee stock that has been demonstrated to provide improved mite control.
Mechanical or physical control - the use of a trapping device or other physical equipment to reduce mite population buildup or reduce high mite numbers
Biological control
No known, effective biological control exists, but efforts to select mushroom mycelium show good promise.
Chemical control
See "Tools for Varroa Management" in Resources (below), for details on chemical controls.
Traynor KS, et al. 2020. Varroa destructor: A Complex Parasite, Crippling Honey Bees Worldwide. Trends in Parasitology 36(7): 592-606. https://www.sciencedirect.com/science/article/pii/S147149222030101X
Milbrath M. 2017. Planning for Varroa. Michigan State University Extension. Accessed 2023. https://static1.squarespace.com/static/56818659c21b86470317d96e/t/5900c9798419c2db7622e85b/1493223802902/MakingAPlanforVarroa_2017.pdf
Sebestyen T. 2021. Integrated Pest Management for honey bees against Varroa destructor. American Bee Journal 161(12): 1341-1345. https://bluetoad.com/publication/?i=728253&p=76&view=issueViewer and https://bluetoad.com/publication/?m=5417&i=728253&view=articleBrowser&article_id=4155681&ver=html5
Honey Bee Health Coalition. 2022. Tools for Varroa Management: A Guide to Effective Varroa Sampling & Control. Honey Bee Health Coalition. Accessed 2023. https://honeybeehealthcoalition.org/wp-content/uploads/2022/08/HBHC-Guide_Varroa-Mgmt_8thEd-082422.pdf
“Low Varroa Growth Part 1”. YouTube, uploaded by University of Guelph Honey Bee Research Centre, 16 Aug 2021. https://www.youtube.com/watch?v=UP77P2HckwQ
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