Varroa destructor (Varroa mite) is an external parasitic mite that attacks and feeds on the honey bees Apis cerana and Apis mellifera. The disease caused by the mites is called varroosis.
The Varroa mite can reproduce only in a honey bee colony. It attaches to the body of the bee and weakens the bee by sucking fat bodies.[1] The species is a vector for at least five debilitating bee viruses,[1] including RNA viruses such as the deformed wing virus (DWV). A significant mite infestation leads to the death of a honey bee colony, usually in the late autumn through early spring. The Varroa mite is the parasite with possibly the most pronounced economic impact on the beekeeping industry. Varroa is considered to be one of multiple stress factors[2] contributing to the higher levels of bee losses around the world.
| Varroa mite | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Arachnida |
| Subclass: | Acari |
| Order: | Mesostigmata |
| Family: | Varroidae |
| Genus: | Varroa |
| Species: | V. destructor |
| Binomial name | |
| Varroa destructor Anderson & Trueman, 2000 | |
Treatments have met with limited success. First, the bees were medicated with fluvalinate, a synthetic pyrethroid, which had about 95% mite falls. However, the last 5% became resistant to it, and later, almost immune. Fluvalinate was followed by coumaphos, which mites also have developed resistance to.[26]
Chemical measures
Varroa mites can be treated with commercially available acaricides.[citation needed] Acaricides must be applied carefully to minimize the contamination of honey that might be consumed by humans. Proper use of miticides also slows the development of resistance by the mites.
Synthetic chemicals[edit]
- Pyrethroid insecticide (fluvalinate) as strips
- Organophosphate insecticide (Coumaphos or Check-mite) as strips
- Manley's Thymol Crystal and surgical spirit recipe with sugar as food[29]
Naturally occurring chemicals[edit]
- Formic acid as vapor or pads (Mite-Away)
- Powdered sugar (Dowda method), talc, or other "safe" powders with a grain size between 5 and 15 μm (0.20 and 0.59 mils) can be sprinkled on the bees.
- Essential oils, especially lemon, mint, and thyme oil[30]
- Sugar esters (Sucrocide) in spray application
- Oxalic acid trickling method or applied as vapor
- Mineral oil (food grade) as vapor and in direct application on paper or cords
- Natural hops compounds in strip application (Hopguard)
However, the most effective long-term way of protecting bees against V. destructor is by breeding bees that are resistant to these mites.[7]
Physical, mechanical, behavioral methods[edit]
Varroa mites can also be controlled through nonchemical means. Most of these controls are intended to reduce the mite population to a manageable level, not to eliminate the mites completely.[citation needed]
- Perforated bottom board method is used by many beekeepers on their hives. When mites occasionally fall off a bee, they must climb back up to parasitize another bee. If the beehive has a screened floor with mesh the right size, the mite falls through and cannot return to the beehive. The screened bottom board is also being credited with increased circulation of air, which reduces condensation in a hive during the winter. Studies at Cornell University done over two years found that screened bottoms have no measurable effect at all.[31] Screened bottom boards with sticky boards (glue traps) separate mites that fall through the screen and the sticky board prevents them from crawling back up.[citation needed]
- Heating method, first used by beekeepers in Eastern Europe in the 1970s, later became a global method. In this method, hive frames are heated to at least 104 °F (40 °C) for several hours at a time, which causes the mites to drop from the bees.[32][33]When combined with the perforated bottom board method, this can control mites sufficiently to aid colony survival.[32] In Germany, anti-varroa heaters are manufactured for use by professional beekeepers. A thermosolar hive has been patented and manufactured in the Czech Republic.[33][34]
- Limited drone brood cell method limits the brood space cell for Varroa mites to inhabit (4.9 mm across—about 0.5 mm smaller than standard), and also enhances the difference in size between worker and drone brood, with the intention of making the drone comb traps more effective in trapping Varroa mites. Small cell foundations have staunch advocates, though controlled studies have been generally inconclusive.[citation needed]
- Comb trapping method (also known as the swarming method) is based on interrupting the honey bee brood cycle. It is an advanced method that removes capped brood from the hive, where the Varroa mites breed. The queen is confined to a comb using a comb cage. At 9-day intervals, the queen is confined to a new comb, and the brood in the old comb is left to be reared. The brood in the previous comb, now capped and infested with Varroa mites, is removed. The cycle is repeated. This complex method can remove up to 80% of Varroa mites in the hive.[citation needed]
- Freezing drone brood method takes advantage of the Varroa mites' preference for longer living drone brood. The beekeeper puts a frame in the hive that is sized to encourage the queen to lay primarily drone brood. Once the brood is capped, the beekeeper removes the frame and puts it in the freezer. This kills the Varroa mites feeding on those bees. It also kills the drone brood, but most hives produce an excess of drone bees, so it is not generally considered a loss. After freezing, the frame can be returned to the hive. The nurse bees clean out the dead brood (and dead mites) and the cycle continues.[citation needed]
- Drone brood excision method is a variation applicable to top bar hives. Honey bees tend to place combs suitable for drone brood along the bottom and outer margins of the comb. Cutting this off at a late stage of development ("purple eye stage") and discarding it reduces the mite load on the colony. It also allows for inspection and counting of mites on the brood.[citation needed]
Genetic engineering[edit]
Researchers have been able to use RNA interference to knock out genes in the Varroa mite. Efforts also have been made to breed for changes in the honey bees.[35] Two strains have been developed in the United States that can detect damaged pupae under cappings and remove them before the infestation spreads further.[36][37] The “IN”/Indiana strain is under development at Purdue University to develop lines that groom off and bite phoretic Varroa to kill the mites.[38][39]
https://en.wikipedia.org/wiki/Varroa_destructor
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