Varroa destructor is an external parasitic
miteMites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
that attacks
honey beeHoney bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
s
Apis ceranaApis cerana, or the Asiatic honey bee , is a species of honey bee found in southern and southeastern Asia, such as China, India, Japan, Malaysia, Nepal, Bangladesh and Papua New Guinea. This species is the sister species of Apis koschevnikovi, and both are in the same subgenus as the Western honey...
and
Apis mellifera. The disease caused by the mites is called
varroatosis.
Varroa destructor can only replicate in a honey bee colony. It attaches at the body of the bee and weakens the bee by sucking
hemolymphHemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
. In this process
RNA virusAn RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
es such as the
deformed wing virus (DWV)Deformed wing virus is an RNA virus, one of 18 known viruses affecting the honey bee, Apis mellifera. The virus was first isolated from a sample of symptomatic honeybees from Japan in the early 1980s and is currently distributed worldwide....
spreads to bees. A significant mite infestation will lead to the death of a honey bee colony, usually in the late autumn through early spring. The
Varroa mite is the parasite with the most pronounced economic impact on the
beekeepingBeekeeping is the maintenance of honey bee colonies, commonly in hives, by humans. A beekeeper keeps bees in order to collect honey and other products of the hive , to pollinate crops, or to produce bees for sale to other beekeepers...
industry. It may be a contributing factor to
colony collapse disorder (CCD)Colony collapse disorder is a phenomenon in which worker bees from a beehive or European honey bee colony abruptly disappear. While such disappearances have occurred throughout the history of apiculture, the term colony collapse disorder was first applied to a drastic rise in the number of...
, as research shows it is the main factor for collapsed colonies in
OntarioOntario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
,
CanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
Physical description
The adult mite is reddish-brown in color; has a flat, button shape; is 1–1.8 mm long and 1.5–2 mm wide; and has eight legs.
Reproduction, infection and hive mortality
Mites reproduce on a 10-day cycle. The female mite enters a honey bee brood cell. As soon as the cell is capped, the
Varroa mite lays eggs on the larva which hatch into several females and typically one male. The young mites hatch in about the same time as the young bee develops and leave the cell with the
hostIn biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
. When the young bee emerges from the cell after pupation the
Varroa mites also leave and spread to other bees and larvae. The mite preferentially infests drone cells.
The adults suck the "blood" of adult honey bees for sustenance, leaving open wounds. The compromised adult bees are more prone to infections. With the exception of some resistance in the Russian strains and
Varroa sensitive hygieneVarroa sensitive hygiene is a behavioral trait of honey bees in which bees detect and remove bee pupae that are infested by the parasitic mite Varroa destructor. V. destructor is considered to be the most dangerous pest problem for honey bees worldwide...
(VSH) developed by the USDA, the European
Apis mellifera bees are almost completely defenseless against these parasites (Russian honey bees are one third to one half less susceptible to mite reproduction).
The model for the
population dynamicsPopulation dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...
is
exponential growthExponential growth occurs when the growth rate of a mathematical function is proportional to the function's current value...
when bee brood are available and exponential decline when no brood is available. In 12 weeks the number of mites in a Western honey bee hive can multiply by (roughly) 12. High mite populations in the autumn can cause a crisis when drone rearing ceases and the mites switch to worker larvae, causing a quick population crash and often hive death.
Varroa mites have been found on flower feeding insects such as the
bumblebeeA bumble bee is any member of the bee genus Bombus, in the family Apidae. There are over 250 known species, existing primarily in the Northern Hemisphere although they are common in New Zealand and in the Australian state of Tasmania.Bumble bees are social insects that are characterised by black...
Bombus pennsylvanicus, the
scarab beetleScarab beetle may refer to these species: * A beetle of the family Scarabaeidae* Scarabaeus sacer, the dung beetle species worshipped by the ancient Egyptians as an embodiment of the god Khepri...
Phanaeus vindexPhanaeus vindex, the rainbow scarab or rainbow scarab beetle is a North American dung beetle, with a range from the eastern US to the Rocky Mountains. The head is a metallic yellow color, and males have a black horn which curves backward toward the thorax. Both sexes have yellow antennae which can...
and the flower-fly
Palpada vinetorum. Although the
Varroa mite cannot reproduce on these insects, its presence on them may be a means by which it spreads short distances (phoresy).
Introduction around the world
- Early 1960s Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, USSR
- 1960s-1970s Eastern Europe
Eastern Europe is the eastern part of Europe. The term has widely disparate geopolitical, geographical, cultural and socioeconomic readings, which makes it highly context-dependent and even volatile, and there are "almost as many definitions of Eastern Europe as there are scholars of the region"...
- 1971 Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
- Late 1970s South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
- 1980 Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
- 1982 France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
- 1984 Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, SpainSpain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, ItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
- 1987 Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
- 1987 USA
- 1989 Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
- 1992 England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
- 2000 New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
(North IslandThe North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
)
- 2006 New Zealand (South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
)
- 2007 Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
As of the second half of 2011, Australia was thought to be free of the mite. In early 2010, an isolated sub-species of bee was discovered in Kufra (south-eastern Libya) that appears to be free of the mite.
Identification
Varroa destructor was, until recently, thought to be a closely related mite species called
Varroa jacobsoniVarroa jacobsoni is a species of mite that parasitises Apis cerana . The more damaging Varroa destructor was previously included under the name V. jacobsoni, but the two species can be separated on the basis of the DNA sequence of the cytochrome oxidase I gene in the mitochondrial DNA....
. Both species parasitize the Asian honey bee,
Apis ceranaApis cerana, or the Asiatic honey bee , is a species of honey bee found in southern and southeastern Asia, such as China, India, Japan, Malaysia, Nepal, Bangladesh and Papua New Guinea. This species is the sister species of Apis koschevnikovi, and both are in the same subgenus as the Western honey...
. However, the species originally described as
V. jacobsoni by Anthonie Cornelis Oudemans in 1904 is not the same species that also attacks
Apis mellifera. The jump to
mellifera probably first took place in the
PhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
in the early 1960s where imported
Apis mellifera came into close contact with infected
Apis cerana. Up until 2000, scientists had not identified
Varroa destructor as a separate species. This late identification in 2000 by Anderson and Trueman corrected some previous confusion and mislabeling in the scientific literature.
Chemical measures
Varroa mites can be treated with commercially available
miticideAcaricides are pesticides that kill members of the Acari group, which includes ticks and mites.Acaricides are used both in medicine and agriculture, although the desired selective toxicity differs between the two fields.-Terminology:...
s.
Miticides must be applied carefully to minimize the contamination of
honeyHoney is a sweet food made by bees using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans...
that might be consumed by humans. Proper use of miticides also slows the development of resistance of the mites.
Synthetic chemicals
- pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
(Apistan) as strips
- organophosphate
An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...
insecticide (Coumaphos (Check-mite)) as strips
- Manley
Robert "Bert" Orlando Beater Manley was a British Beekeeper, an authority on commercial honey farming and developer of the popular Manley moveable frame hives and frame systems.-Achievements:...
's Thymol Crystal and surgical spirit recipe with sugar as food.
Natural occurring chemicals
- Essential oil
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...
s, especially lemon, mint and thyme oil
- sugar esters
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
(Sucrocide) in spray application
- oxalic acid
Oxalic acid is an organic compound with the formula H2C2O4. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate , is a chelating agent for metal cations...
trickling method or applied as vapor
- formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
as vapor or pads
- Foodgrade mineral oil as vapor and in direct application on paper or cords.
Physical or mechanical methods
Varroa mites can also be controlled through non-chemical means. Most of these controls are intended to reduce the mite population to a manageable level, not to eliminate the mites completely.
- Many beekeepers use a screened bottom board on their hives. When mites occasionally fall off a bee, they must climb back up to parasitize a new bee. If the beehive has a screened floor with mesh the right size, the mite will fall through and can not 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
Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
done over two years found that screened bottoms have no measurable effect at all. Northeast Beekeeper Vol 1 #1 Jan 2004)
- Screened bottom board with sticky board. It separates mites that fall through the screen and the sticky board prevents them from crawling back up.
- Small cell foundation (4.9 mm across—about 0.5 mm smaller than standard) is believed to limit the space in each cell that Varroa mites have in which to inhabit and also to enhance 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 foundation has staunch advocates though controlled studies have been generally inconclusive.
- Comb trapping is an advanced method that removes capped brood from the hive, where the Varroa mites breed. The queen is confined to comb A using a comb cage. After nine days the queen is confined to a new comb—comb B—and the brood in comb A is left to be reared. Nine days later the brood in comb A—now capped and infested with Varroa mites—is removed. The queen is then removed from comb B and placed on to comb C, with the brood in comb B left to be reared. Nine days later comb B is removed and the queen is excluded from comb B. Nine days later comb C is removed. This complex method can remove up to 80% of Varroa mites in the hive.
Behavioral methods
- Powdered sugar (Dowda method), talc or other "safe" powders with a grain size between 5 and 15 micrometres can be sprinkled on the bees. The powder does not harm the bees (and, in the case of sugar, can even become a small food source), but does interfere with the mite's ability to maintain its hold on the bee. It is also believed to increase the bees' grooming behavior. This causes a certain percentage of mites to become dislodged. Powdered sugar works best as an amplifier of the effects of a screened bottom board.
- Freezing drone brood takes advantage of Varroa mites' preference for longer living drone
Drones are male honey bees. They develop from eggs that have not been fertilized, and they cannot sting, since the worker bee's stinger is a modified ovipositor .-Etymology:...
brood. The beekeeper will put 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 that are feeding off of 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 will clean out the dead brood (and dead mites) and the cycle continues.
- Drone brood excision is a variation applicable to top bar hives. Honey bees tend to place comb 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 varroa on the brood.
- Swarming or queen-arrest method. By interrupting the honey bee brood cycle, mites reproduction is also blocked.
- Hygienic behavior. Hygienic behavior is biological behavior with genetic traits that can be bred into bees. This behavior causes bees to smell infected brood and remove them before the infestation spreads further.
Genetic engineering
Researchers have been able to use
RNA interferenceRNA interference is a process within living cells that moderates the activity of their genes. Historically, it was known by other names, including co-suppression, post transcriptional gene silencing , and quelling. Only after these apparently unrelated processes were fully understood did it become...
to
knockoutA gene knockout is a genetic technique in which one of an organism's genes is made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...
genes in the Varroa mite.
Varroatosis
The infection and subsequent
parasitic diseaseA parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases. Parasitic diseases can affect practically all living organisms, including plants and mammals...
caused by varroa mites is called
varroatosis. Its treatment has been of limited success. First the bees were medicated with
fluvalinateFluvalinate is a synthetic pyrethroid commonly used to control varroa mites in honey bee colonies....
which had about 95% mite falls. However the last five percent became resistant to it and later, almost immune. Fluvalinate was followed by
coumaphosCoumaphos is a non-volatile, fat-soluble phosphorothioate with ectoparasiticide properties: it kills insects and mites. It is well known under manufacturer brand-names as a dip or wash, used on farm and domestic animals to control ticks, mites, flies and fleas...
.
Further reading
- Tracheal and Varroa Mite Controls Apiculture Factsheet #221, Ministry of Agriculture, Food and Fisheries, Government of British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
; April 2004
- Oils for Varroa Control Botanicals For Mite Control, Canadian Honey Council, 3/16/2003
External links