Photo 3. An adult female varroa mite, Varroa destructor, feeds on the midsection of a developing worker bee.
Varroa destructor; previously the mite was known as Varroa jacobsoni, but in 2000 molecular analysis discovered that there were two species (see Fact Sheet no. 326). The effect of the mite on the European honeybee is referred to as 'varroosis of honey bees'.
Worldwide. Asia, Africa, North, South and Central America, the Caribbean, Europe, Oceania. Australia is the only continent yet free from the mite. It is recorded from French Polynesia, New Caledonia, and New Zealand. As of 2017, only Australia is free from infestation.
The distribution of the mite increased greatly after colonies of the European honeybee were taken to Asia and became infested with the mite from Varroa jacobsoni. This occurred in the last 50-100 years (possibly in the 1950s).
European honeybee, Asian honeybee (minor host).
Infestations of Varroa destructor are invariably serious leading to a disease known as 'varroosis'. There have been suggestions that the mite is a factor in 'colony collapse disorder' when most of the workers disappear. Varroa mites can also spread viruses, further affecting the health of colonies. In fact, there is speculation that the viruses not the mites are the cause of most damage to the bees.
Varroa destructor usually takes some time before being noticed within a colony, sometimes up to 2 years. However, severe infestations lead to:
The adult female mite is reddish-brown, while the male is white. They are flat, oval, 1–1.8 mm long, 1.5–2 mm wide (Photos 1&2). Adult males are smaller. On adult bees, the mites occur on the thorax or in the abdominal folds.
Varroa destructor reproduces on the larvae of drones and workers of the European honeybee. The bees do not have the grooming behaviour of the Asian honeybee. The latter, can detect and remove the mites from worker bee brood cells.
One or two female varroa mites enter a brood cell before it is capped (closed) and lay 5-6 eggs each, which are difficult to see with the unaided eye. The newly hatched nymph mites feed on the bee larvae and pupae (Photo 3). Once nymphs mature, they mate and the male dies. The females attach themselves to adult bees and feed off their haemolymph (blood) (Photo 4). They emerge from the brood cells with the honeybees (Photo 5).
The rate of increase in the mite population depends on the number of females present, the type of brood (whether drone or worker), and how long brood is available throughout the year. More female mites are produced in drone cells than worker as they take 3 days longer to mature than workers.
Spread occurs easily within the hive as the mites are mobile. After emerging, they may remain attached to the original adult, fall off and find other adults to infest, or enter a brood cell. They may spread in other ways: i) bees infested with mites enter neighbouring hives to rob nectar; ii) bees enter the hives of other colonies by mistake - they drift into another colony; or iii) when beekeepers place infested "combs" (hexagonal cells where queens lay eggs) in healthy hives. Long distance spread may also occur during swarming. They may be dispersed, too, by bumblebees (Bombus species), although they do not reproduce on them.
The mites live for about 2-3 months. When the colony is not breeding and brood is absent, the mites survive fastened to adults, feeding on their haemolymph. They are obligate parasitess of honeybees and do not survive long away from the host.
Varroa destructor is responsible for the death of European honeybees and the collapse of colonies wherever it is present worldwide. Millions of colonies have been destroyed and billions of dollars lost. Economic consequences are large: apart from loss of honey, there is the risk to crop pollination. A third of the crops eaten by human are pollinated by insects, of which 80% are European honeybees. Further, mite transmit viruses, increasing their impact further.
There are accepted ways of monitoring for mites, and three methods are provided. Early detection and reporting is important as it improves the chances of containing and eradicating introductions, therefore, monitoring should be done quarterly at least:
Method 1 (Uncapping drone cells)
Method 2 (Sugar shaking)
Method 3 (Sticky screens)
The two species, Varroa jacobsoni and the more damaging Varroa destructor can be separated by DNA analysis.
Although widely distributed, there are Pacific island countries, for instance, still free from the introduction of Varroa destructor (and Varroa jacobsoni, and newly discovered strains). Australia is free from the mite, too. Those countries, but also others where varroa mites are already present, may wish to enact legislation and devise codes of conduct to minimise the risk of introduction of exotic bee pests and diseases as well as managing those that are endemic. Such a code, developed in 2016 for Australia is provided as an example: http://beeaware.org.au/wp-content/uploads/2017/05/Australian-Honey-Bee-Industry-Biosecurity-Code-of-Practice.pdf, and the Biosecurity manual for beekeepers: http://www.planthealthaustralia.com.au/wp-content/uploads/2016/02/Biosecurity-Manual-for-Beekeepers.pdf.
There are a number of control measures aimed at commercial beekeepers as well as the general public. Some of these may form part of national biosecurity legislation to contain the entry of varroa mites and the spread of endemic pests.
Surveys and sampling (for purposes of biosecurity):
Public awareness to control mites:
Physical methods to control mites:
Sanitation to control mites:
Russian bees, a strain related to the European honeybee that have very low mite populations in their colonies have been introduced to other countries. Russian queen bees are now becoming popular with beekeepers.
Treatment of hives and equipment:
There are times when it is necessary to sterilise hives and equipment. This might be when there has been a mite infestation, the hives and equipment are second-hand or before storage. EITHER:
Treatment of mites on the bees:
AUTHOR Grahame Jackson
Information from CABI (2015) Varroosis of honey bees. Crop Protection Compendium (www.cabi.org/cpc); and BeeAware. Plant Health Australia. http://beeaware.org.au/archive-pest/varroa-mites/#ad-image-0); and Biosecurity manual for beekeepers. (http://www.planthealthaustralia.com.au/wp-content/uploads/2016/02/Biosecurity-Manual-for-Beekeepers.pdf); and Varroa mite detection in Townsville. Department of Agriculture and Fisheries. Queensland Government. (https://www.daf.qld.gov.au/animal-industries/bees/diseases-and-pests/asian-honey-bees/general-information-on-varroa-mites); and from Varroa mite. Entomology & Nematology. UF/IFAS, University of Florida. (http://entomology.ifas.ufl.edu/creatures/misc/bees/varroa_mite.htm). Photos 2-4 Scott Bauer, USDA Agricultural Research Service, Bugwood.org. Photo 1 Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org. Photo 5 Stephen Ausmus, USDA Agricultural Research Service, Bugwood.org
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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