Varroa mites

Signs or indications

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.

Description

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.

Control of varroa mites

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

  • situating colonies in the sun
  • providing good air circulation within a colony
  • giving colonies a distinctive hive address

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

  • traps such as drone brood trapping
  • colony brood break
  • bottom board screen

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.

Resources

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

  Varroa destructor  adult mite; photo by Gilles San Martin
Varroa destructor adult mite; photo by Gilles San Martin
 Varroa mite; photo by Scott Bauer, USDA
Varroa mite; photo by Scott Bauer, USDA
 Varroa mite adult (left),  Tropilaelaps  adult (right); photo by USDA
Varroa mite adult (left), Tropilaelaps adult (right); photo by USDA
 Varroa mite on an adult; photo by Robert Snyder
Varroa mite on an adult; photo by Robert Snyder
 Two Varroa mites on worker abdomen; photo by AbsoluteFolly, Flickr, CC BY-NC-ND 2.0 https://creativecommons.org/licenses/by-nc-nd/2.0
Two Varroa mites on worker abdomen; photo by AbsoluteFolly, Flickr, CC BY-NC-ND 2.0 https://creativecommons.org/licenses/by-nc-nd/2.0
 Varroa female mite on worker pupa; photo by Gilles San Martin
Varroa female mite on worker pupa; photo by Gilles San Martin
 Varroa mite foundress female (arrow at right) and two immature developing offspring; photo by The BeeMD photo collection
Varroa mite foundress female (arrow at right) and two immature developing offspring; photo by The BeeMD photo collection
 Varroa mite on head of worker pupa; photo by Gilles San Martin
Varroa mite on head of worker pupa; photo by Gilles San Martin
 Varoa mite with its offspring in cell; photo by Rusty Burlew, HoneyBeeSuite.com
Varoa mite with its offspring in cell; photo by Rusty Burlew, HoneyBeeSuite.com
 Adult worker with two Varroa on thorax and deformed wing virus; photo by The BeeMD photo collection
Adult worker with two Varroa on thorax and deformed wing virus; photo by The BeeMD photo collection
 Adult female (lower right), adult male (upper left), and immature stages of Varroa mite; photo by Oregon state University
Adult female (lower right), adult male (upper left), and immature stages of Varroa mite; photo by Oregon state University
 Varroa mites between worker ventral abdominal segments; photo by Scott Koppa
Varroa mites between worker ventral abdominal segments; photo by Scott Koppa
 Varroa mite on drone pupa; photo by Dewey M. Caron
Varroa mite on drone pupa; photo by Dewey M. Caron
 Scraping drone comb to flatten the mite growth curve during spring; photo by Robyn Underwood
Scraping drone comb to flatten the mite growth curve during spring; photo by Robyn Underwood
 Mite poop seen as tiny white dots on brood cell walls: photo by Anna Ashby
Mite poop seen as tiny white dots on brood cell walls: photo by Anna Ashby