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   Varroa destructor (arachnid)
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      Bee damaged by Deformed wing virus (DWV), (Photo: Ingemar Fries) - Click for full size   Varroa female - Click for full size
    Taxonomic name: Varroa destructor Anderson & Trueman, 2000
    Synonyms:
    Common names: varroa mite (English)
    Organism type: arachnid
    Varroa destructor is an external parasite found throughout most of the world that attacks all lifecycle stages of a broad range of honeybees. Varroa destructor sucks the blood from both the adults and the developing brood, weakening and shortening the life span of bees upon which they feed. Untreated infestations that are allowed to increase will destroy entire honeybee colonies. The movement of infested colonies of bees for pollination has led to the rapid local spread of this mite. Although Varroa destructor can only reproduce on honeybees, other insects may also assist in spreading it.
    Description
    Adult female mites are reddish-brown in colour, have eight legs and a flattened oval shape. Denmark et al. (2000) reports that the females measure 1.00-1.77mm long and 1.50-1.99mm wide. Their curved bodies fit into abdominal folds of the adult bee and are held there by the shape and arrangement of ventral setae (the stiff hairs on the abdomen). This protects them from the bee's normal cleaning habits. Adult males only occur in sealed brood and are yellowish with lightly tanned legs, a spherical body shape, and measure 0.75 - 0.91mm long and 0.71 - 0.88 wide. The male chelicerae (a pair of fanglike appendages near the mouth) are modified for transferring sperm.

    Please see PaDIL (Pests and Diseases Image Library) Species Content Page Non-insects: Varroa Mite for high quality diagnostic and overview images.

    Similar Species
    Braula coeca

    More
    Occurs in:
    agricultural areas, natural forests, planted forests, riparian zones, ruderal/disturbed, urban areas
    Habitat description
    V. destructor is found on a range of honeybees, according to Denmark (2000), including the Asian honey bee species Apis cerana and A. koschevnikovi, and on all races of the European bee A. mellifera. In Florida, V. destructor has been found on flower feeding-insects Bombus pennsylvanicus and Palpada vinetorum but this association is probably incidental and contributes little, if anything, to the spread of this parasite. The mite is spread between colonies on live bees carrying mites.
    General impacts
    The mite is devastating to beekeeping in most parts of the world if the mite population is not controlled. On the other hand, if it is, the impact is minor or nil. It is increasingly clear that the negative effects from the mite primarily is related to virus infections where the mite triggers replication of dormant infections that become overt. The mite also vectors these virus infections and introduces transmission patterns that were not there before. Deformed wing virus (DWV), acute bee paralysis virus (APV) and slow paralysis virus (SPV) are probably the most important types in this context - all RNA viruses that replicate upon injection in bee haemolymph (Fries, I., pers.comm., 2004).

    It has been reported in Europe that weak colonies are subject to being robbed by stronger colonies and may die within three to four years from the lack of worker bees to manage the brood and gather nectar. In Florida, infested colonies have died within seven months, probably due to the weather conditions where bees rear brood throughout the year and, thus, provide a continous source for mite population development. The original host, Apis cerana, supports populations of mites without collapsing and Apis mellifera scutellata in South America (the Africanized honey bee) seems to have some resistance or tolerance to the mite, whereas this resistance is not found in the same bee race in Africa where the mite was recently introduced. V. destructor is beyond doubt the most serious pests currently known for A. mellifera, which is a widely domesticated honeybee (Denmark et al. 2000).

    MAF, NZ summarises the damage to bee colonies as follows: In the absence of treatment, an infested bee colony typically dies when the varroa population reaches a certain level. This "threshold" level appears to vary between locations and seasons. The actual cause of colony death is uncertain, but is likely to be the cumulative effect of the following effects:
    decreased weight of adult bees;
    decreased life-span of adult bees;
    virus infections, transmitted by varroa feeding on pupae;
    deformed wings and abdomens, probably resulting from virus infestations; and
    reduced numbers of drone bees, and increased drone infertility.
    Colony death often occurs during the autumn/winter period, when the effects of varroa combine with seasonal population decreases and other stress factors (MAF, NZ., 2003).

    Pollination of many significant crop species in the horticulture, arable and pastoral sectors is dependent on honey bees. A reduction in pollination of horticultural and arable crops could result in decreased overall yields and crop quality.
    The cost of varroa control per colony (estimated at between $20 to $50 per year in NZ), adds significantly to the operating costs of beekeepers.
    Varroa is likely to have a significant impact on beekeepers producing certified organic products. While there are varroacidal agents that are acceptable to organic certification agencies, they are generally less effective than their synthetic equivalents. It is likely that some organic beekeepers will give up their organic status to simplify varroa management (MAF, NZ., 2003).

    Notes
    Varroa jacobsoni is the old name for the varroa mite; the mite that is known to infest the A.mellifera colonies was found to be a different species and has been named Varroa destructor. Anderson and Trueman (2000), after studying mtDNA Co-I gene sequences and morphological characters of many populations of V. jacobsoni from different parts of the world, considered it to be a species complex and split it into two species Varroa jacobsoni s.s. infests Apis cerana F. in the Malaysia-Indonesia region. Varroa destructor Anderson & Trueman, 2000 infests its natural host A. cerana on mainland Asia and also A. mellifera L. worldwide.
    Geographical range
    Native range: V. destructor came from the far east, where it is a parasite on the Asiatic honeybee species A. cerana.
    Known introduced range:V. destructor is found on all continents except Australia. It is not known where the adaption of the parasite to European honey bee took place.
    Introduction pathways to new locations
    Agriculture: Importation of queen bees from infested areas by bee farmers introduced the mite into new areas of the world (Denmark et al., 2000)
    Ignorant possession: Farmers importing queen bees, did not realize the were also importing the Varroa destructor (Denmark et al. 2000)


    Local dispersal methods
    Agriculture (local): Mites are spread from colony to colony by drifting workers and drones within an apiary and when honeybees rob smaller colonies (Bessin, 2001).
    Natural dispersal (local): The movement of infested colonies of bees for pollination has led to the rapid local spread of this mite (Denmark et al., 2000).
    On animals: Denmark et al. (2000) notes that in Florida, V. destructor has been found on flower feeding-insects, such as Bombus pennsylvanicus, Palpada vinetorum, and Phanaeus vindex. Although V. destructor can only reproduce on honeybees, these insects are a means of spreading the mite short distances.
    Management information
    Various management methods have been developed for the control of V. destructor, and researchers continue to search for additional effective methods. The simple way to monitor the mite is to investigate colony debris where dead adult mites can be found if present. This requires a screen bottom board so the colony debris is not cleaned out by the bees. Instant results can also be achieved by the ether roll method where adult bees are shaken in a jar with ether, and the mites dislodge and adhere to the glass wall.
    For details on management options, please see management information.
    Nutrition
    According to CHBRC (UNDATED), adult mites are able to pierce both the soft skin of the honeybee larva and tougher integument between the thoracic segments of adult bees with their specialized mouthparts. Not only do the mites remove hemolymph (analogous to blood) from their host, but they also inject their own saliva, which like other arachnids, contains proteases (various enzymes that predigest the bee tissues). With digestion occurring externally, the mite simply slurps up the liquid meal.
    Reproduction
    According to Denmark et al. (2000) the female mite lays eggs in bee brood cells. The developing mites feed on developing honeybee larvae, with a distinct preference for drone brood according to Bessin (2001). Denmark et al. (2000) goes on to state that males and females copulate inside the cell. The male dies, but the pregnant females emerge from the cell along with their bee host. They then seek another cell to repeat the cycle. The length of the postcapping period in honeybees may be an important factor determining the speed of the mite population increase. The longer the postcapping time (the time after which honey seals, or caps, the honeycomb with wax), the more time is provided for female mites to develop.
    Lifecycle stages
    Varroa is an external parasite that lives exclusively on honeybees, feeding on their haemolymph (blood). To breed, the adult female mite enters a brood cell just before the cell is capped over, where she remains in the brood food until the cell is sealed. She then feeds on the immature bee and begins to lay eggs. Mating between mite offspring (brother and sister) occurs within the cell. Mature female mites leave the cell when the host bee emerges. Males and any remaining immature females die, unable to survive outside the sealed cell. With heavy infestation, two or more female mites may enter the same cell to breed. Mites prefer to breed in drone brood, but are also well suited to infest worker cells of the European honeybee. In winter, when brood rearing is restricted, mites over-winter solely on the bodies of the adult bees within the winter cluster, until brood rearing commences the following spring (CSL, 2003).

    Denmark et al. (2000) describes the life cycle of V. destructor as very much synchronized with that of its honeybee host. It is thought that the hormones or pheromones of honeybees are necessary for the mite to complete its development. CHBRC (UNDATED) found that the average life expectancy for V. destructor is about 50 days during the breeding season.In bees without brood, the adult female mites can survive several months, feeding on the adult bees.

    Reviewed by: Ingemar Fries, Department of Entomology, Swedish University of Agricultural Sciences
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Tuesday, 20 June 2006


ISSG Landcare Research NBII IUCN University of Auckland