Photographer:Scott Bauer Affiliation: USDA Agricultural Research Service Source:www.bugwood.org Copyright: CC BY 3.0
This arachnid is an external parasite of honey bees (Apis spp.). Originally Varroa destructor was an ectoparasite of the Asian honey bee (Apis cerana) but eventually was able to use the European honey bee (Apis melifera) as a host, which was confirmed in 1963 in Singapore. It has a flattened and oval body with eight legs. Adult females are reddish brown measuring about .06 inches in width. Males are yellowish with tan legs and are smaller and more spherical in shape.
Heavy infestations of these mites can cause newly-emerged bees to have malformed wings, legs and bodies. When they are parasitizing adult bees they affect flight, orientation and cause the bees to get lost and not be able to return to their hive. When worker bees disappear or die off, this severely weakens the colony because no bees are able to care for the larval bees. Weak colonies are susceptible to having their honey stores robbed by stronger hives. Eventually, the colony dies. Varroa destructor is also known to carry several viruses that are fatal to bees including: deformed wing virus, acute bee paralysis virus and slow paralysis virus. These viruses result in a condition called “parasitic mite syndrome” and a colony can be destroyed in a few months. With bees being an ecologically and economically important insect, the control of this mite is a necessity to ensure the continuing prosperity of the apiary market.
The life cycle of this mite is in conjunction with the honey bee life cycle. Female Varroa destructor mites enter the brood cells of honey bees, just before the worker bees cap the cell, and lays eggs on the larval bee. About three days later, the unfertilized egg becomes a male mite. The male and female mites then reproduce about 1 fertilized egg/ 30 hours; these all become females. All immature mites feed on the bee larvae (pictured above on the left) before the bee emerges from its cell. It usually takes 5 to 8 days for the females to mature and the male mite dies in the cell. Only mated females will leave the cell on the host bee to then seek out new brood cells, where the process begins again. The average lifespan is about 50 days during the breeding season. In the winter, mites solely live on adult bees in the hive and adult mites can only survive a few days without bees.
A single varroa mite was discovered in Maryland in 1979 through an unknown source. By 1987 is appeared in both Florida and Wisconsin, since then it spread rapidly throughout the United States. That last state to be invaded was Hawaii in 2007 on the island of Oahu but the following year it was established on all Hawaiian Islands.
Mainland Asia and Japan
U.S. Present: All United States; in both wild and managed honey bee colonies
U.S. Habitat: Varroa mites are usually found on the thorax and abdomens of larvae, pupae and adults on all strains of the European and Africanized honey bee. This mite has also been found on the American bumblebee, the flower fly and the rainbow scarab beetle; but it is not able to reproduce on them.
A common treatment involves hanging strips infused with Apistan (fluvalinate-based treatment) in the brood nest for about a month. As the dead mites fall off bees, they can be collected on sticky paper placed on the bottom of the hive. This product allows detection of low level infestation and can be used as a control measure. The problem is that the mites can become resistant to Apistan so there are other control chemicals out there CheckMite+ (coumaphos- based) but the base chemical is a dangerous organophosphate and others that are thymol and fenpyroximate based. However, some mites in the United States have shown a natural resistance to coumaphos-based chemicals.
There are some bio-controls that are being investigated like the fungus Metarhizium anisopliae which is lethal to Varroa destructor. Another possibility is genetically engineering bees that are resistant to mite infestation. It is important to constantly survey bee colonies for the presence of the mite. Any new bee-farming colonies that are found to have the mites should be quarantined to prevent mites from spreading to other hives.
Rosenkranz, Peter, Pia Aumeier, and Bettina Ziegelmann. 2010. Biology and control of Varroa destructor. Journal of invertebrate pathology 103:S96-S119.
Spivak, Marla, and Gary S. Reuter. 2001. Varroa destructor infestation in untreated honey bee (Hymenoptera: Apidae) colonies selected for hygienic behavior. Journal of economic entomology 94(2):326-331.