Varroa destructor is an external parasitic
miteMites, along with ticks, belong to the subclass Acarina and the class Arachnida. Mites are among the most diverse and successful of all the invertebrate groups. They have exploited an incredible array of habitats, and because of their small size most go totally unnoticed...
that attacks
honey beeHoney bees are a subset of bees, 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 , are small honey bees of southern and southeastern Asia, such as China, India, Japan, Malaysia, Nepal, Bangladesh and Papua New Guinea...
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 the blood analogue used by all arthropods and most mollusks that have an open circulatory system.In these animals there is no distinction between blood and interstitial fluid. The liquid fills all of the interior of the body and surrounds all cells...
. In this process the mite spreads
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 like
Deformed Wing VirusDeformed 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....
to the bee. A significant mite infestation will lead to the death of a honey bee colony, usually in the late autumn through early spring.
Varroa destructor is an external parasitic
miteMites, along with ticks, belong to the subclass Acarina and the class Arachnida. Mites are among the most diverse and successful of all the invertebrate groups. They have exploited an incredible array of habitats, and because of their small size most go totally unnoticed...
that attacks
honey beeHoney bees are a subset of bees, 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 , are small honey bees of southern and southeastern Asia, such as China, India, Japan, Malaysia, Nepal, Bangladesh and Papua New Guinea...
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 the blood analogue used by all arthropods and most mollusks that have an open circulatory system.In these animals there is no distinction between blood and interstitial fluid. The liquid fills all of the interior of the body and surrounds all cells...
. In this process the mite spreads
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 like
Deformed Wing VirusDeformed 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....
to the bee. 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 beeswax, to pollinate crops, or to produce bees for sale to other beekeepers. A location where bees are kept is called an apiary.-Origins:There are more than...
industry. It may be a contributing factor to
Colony Collapse Disorder (CCD)Colony collapse disorder or sometimes honey bee depopulation syndrome is a phenomenon in which worker bees from a beehive or European honey bee colony abruptly disappear...
which is threatening hives throughout North America.
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, 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). Eastern
Apis ceranaApis cerana, or the Asiatic honey bee , are small honey bees of southern and southeastern Asia, such as China, India, Japan, Malaysia, Nepal, Bangladesh and Papua New Guinea...
honey bee has developed grooming procedures that remove these parasites so they are not a threat to these hives.
The model for the
population dynamicsPopulation dynamics is the branch of life sciences that studies short- 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 fall 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 bumblebee is any member of the bee genus Bombus, in the family Apidae. There are over 250 known species, existing primarily in the Northern Hemisphere....
Bombus pennsylvanicus, the scarab beetle
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 (Kevan
et al. 1990). 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
is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of 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 a region lying in the Eastern part of Europe. The term is highly context-dependent 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 a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
- Late 1970s South America
South America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
- 1982 France
France , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
- 1984 Switzerland
Switzerland , officially the Swiss Confederation , is a federal republic consisting of 26 states named cantons, with Bern as the seat of the federal authorities...
, SpainSpain , officially the Kingdom of Spain , is a country located in southwestern Europe on the Iberian Peninsula.
[The Spanish constitution does not establish any official denomination of the country, even though España , Estado español and Nación española are used interchangeably...]
, ItalyItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
- 1987 Portugal
Portugal , officially the Portuguese Republic , is a country located in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of mainland Europe and is bordered by the Atlantic Ocean to the west and south and by Spain to the north and east...
- 1987 USA
- 1989 Canada
Canada is a country occupying most of northern North America, extending 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 and the North Sea to the east, with 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, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
(North IslandThe North Island is one of the two main islands of New Zealand, separated from the 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 19 islands and 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. Excluding Midway, which is an unincorporated territory of the...
Identification
Varroa destructor was, until recently, thought to be a closely related mite species called
Varroa jacobsoniVarroa jacobsoni mites are a relatively benign parasite of Apis cerana .Until very recently it was thought that they were the cause of the varroatosis, a parasitic disease that plagues Western honey bees, Apis mellifera, since the early 1960s...
. Both species parasitize the Asian honey bee,
Apis ceranaApis cerana, or the Asiatic honey bee , are small honey bees of southern and southeastern Asia, such as China, India, Japan, Malaysia, Nepal, Bangladesh and Papua New Guinea...
. However, the species originally described as
V. jacobsoni by 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 with Manila as its capital city. It comprises 7,107 islands in the western Pacific Ocean....
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. As of 2005, the only
Varroa mites that can reproduce in colonies of
Apis mellifera (Western honeybee) are the Korea and Japan/Thailand genotypes of
Varroa destructor.
Chemical measures
Varroa mites can be treated with commercially-available
miticideMiticides or acaricides are pesticides that kill mites. Antibiotic miticides, carbamate miticides, formamidine miticides, mite growth regulators, organochlorine, permethrin and organophosphate miticides are all in this category. Diatomaceous earth will also kill mites by disrupting the cuticle,...
s.
Miticides must be applied carefully to minimize the contamination of
honeyHoney is a sweet food made by some insects 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 a synthetic chemical compound similar to the natural chemical pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major proportion of the synthetic insecticide market and are common in commercial products such as 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 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 the chemical compound with the formula C2O22 or HOOCCOOH. This colourless solid is a relatively strong carboxylic acid, being about 3,000 times stronger than acetic acid. The dianion, known as oxalate, is a reducing agent as well as a ligand for...
trickling method or applied as vapor (Dany's BienenWohl or VARROX-Vaporiser)
- formic acid
Formic acid is the simplest carboxylic acid. Its formula is HCOOH or CH2O2. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings.In nature, it is found in the stings and bites of many insects of the order...
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 a private university located in Ithaca, New York, USA, that is a member of the Ivy League.Cornell counts more than 255,000 living alumni, 28 Rhodes Scholars and 41 Nobel laureates affiliated with the university as faculty or students...
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 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. Drones develop from eggs that have not been fertilized.-Drone Genetics:Drones carry only one type of allele because they are haploid ; thus, they are also called hemizygous...
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.
Varroatosis
The infection and subsequent
parasitic diseaseA parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause disease per se. Parasitic diseases can affect practically all living organisms, from plants to 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 organophosphate 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 all sorts of ticks, mites, flies and fleas...
.
External links
The
Swiss Bee Research Centre scientifically investigated the life cycle of the varroa in the capped cell and described it in a paper
(A Look under the cap).