Talking About Varroa

This article was published in the March 2010 issue of Bee Craft. Parts 2 and 3 (looking at monitoring and control of Varroa) were published in the April and May 2010 issue. To subscribe to the 12 monthly 2010 issues of Bee Craft in digital format, click here.

Talking about Varroa: Part 1

Pam Gregory, MSc, NDB

We look back over the 18 years since Varroa destructor was found in the UK

THOSE OF us who were beekeepers in 1992 when the parasitic mite Varroa destructor came to the UK saw a veritable sea change in beekeeping over the next few years. As one of the Welsh bee inspectors put it at the time:

‘We will lose the quaintness from beekeeping.’

How right he was. Varroa has changed the nature of beekeeping from a then rather eccentric, happy-go-lucky activity to a much more professional pastime today. Recent successful British Beekeepers’ Association (BBKA) efforts to raise the profile of bees have resulted in an unprecedented uptake of beekeeping, which is excellent news for the craft. New beekeepers take dealing with varroa mites in their stride but it is still one of the most significant causes of bee losses in the UK and its significance and complexity should not be underestimated.


Varroa destructor is an external parasite that feeds on adult, larval and pupal honey bees. Its whole life cycle takes place within the honey bee colony. It is an exotic mite that originally crossed the species barrier from the Asian hive bee (Apis cerana) to our own Western honey bee (Apis mellifera).

Varroa mites were first described by Oudemans in 1904 from observations made in Java on the cells of Apis cerana and were first identified on Apis mellifera in 1958 in Japan (Bailey and Ball 1991). Later, the Australian researchers Anderson and Trueman (2000) discovered that varroa mites could be divided into two distinct species – the original Varroa jacobsoni associated with Apis cerana in Malaya and Indonesia and the aptly named Varroa destructor that is parasitic on Apis cerana in mainland Asia and on Apis mellifera worldwide.

Varroa destructor is further divided into a number of haplotypes of which the most virulent Korean strain has become widespread in melliferan honey bees throughout Europe, Africa, the Middle East, Asia and North and South America.

The varroa mite spread rapidly throughout the world (with the major exception of Australia which has yet to succumb), apparently by normal channels of international trade. We have become very efficient at globalising bee diseases.

Varroa destructor is now found in most colonies in the UK and beekeepers have to monitor and control mite levels – Photo: National Bee Unit


The first mites were discovered in the UK in 1992 by two enthusiastic Devon beginners, no doubt because beginners are frequently the people who look most carefully at their bees and are keenest to learn.

The first reaction was panic, furious anger and looking for someone to blame for the disaster. Amid widespread rumours apportioning blame, the reality was that the first findings were in areas near major international shipping terminals: Plymouth in Devon, Felixstowe in East Anglia and the Isle of Wight in Hampshire. Varroa was thought to have been in the UK for some time before it was discovered, giving it plenty of time to spread unnoticed.


Once it was discovered, people were desperate for easy solutions and ways of preventing it from spreading, and controversy about dealing with the mite raged between beekeepers. Radical eradication programmes, statutory infected area controls, limiting bee movements, utilising mountain ranges and sea channels and other natural or regulatory controls were all proposed to help to slow the mite’s spread.

Despite intense beekeeper vigilance and statutory controls, varroa dispersed through almost the whole country within six years and colony losses ran, on average, at about 30%.


The life cycle of the varroa mite consists of a phoretic stage, when the mites live and move about on the adult bees, and a reproductive phase that is carried out inside the sealed brood cells.

The gravid female mite nips into a brood cell just at the point of cell sealing and hides in the brood food. Once the cell is capped, the mother mite establishes a feeding site on the larva where both she and her offspring can feed from the larval haemolymph (blood).

About 60 hours after cell sealing, the mother mite lays her first egg. This always develops into a male mite, which takes a further five days to mature. Four or five more eggs are laid at about 30-hour intervals and these all develop into female mites that take seven to eight days to develop. Mating between male and female (normally brother and sister) takes place inside the sealed cell and the male never emerges into the colony.

The number of females that can mature depends on the development time of the honey bee larva. Only mites that have reached maturity by the time the cell is opened by the emerging bee will survive. For this reason, the mites prefer drone brood which has a longer development period allowing the development of two or three larvae as opposed to an absolute maximum of two in a worker brood cell.

In the breeding season, female varroa mites live for two to three months, while during the winter or other broodless periods, they can live longer (in a similar manner to ‘winter bees’). During this time the mites feed on the adult bees where their flattened body shape allows them to slip neatly between the abdominal segments and their sharp mouthparts can pierce the bee’s body. Mites cannot survive more than a few days without bees to feed on (so they will not survive on empty combs or equipment).

To control varroa levels, beekeepers need to monitor mite numbers in colonies. This can be done with an open-mesh floor and collecting tray. Colonies should be treated when the threshold level is approached – Photo: National Bee Unit


The control of varroa is relatively simple. You look for it (preferably quantitatively) and then treat it before it reaches a predetermined critical level or threshold. Small numbers of mites do not cause any obvious harm to the bees but as the number of mites rises, so does the potential for harmful effects on the bees. There is currently no clearly defined threshold at which this might occur.

In the UK we use a total mite population per colony of 1000 which can be determined by regular monitoring (DEFRA, 2005). We will come back to this practical stuff in a later article.


In the early days of varroa infestation in the UK, beekeepers were able to control the mites using synthetic pyrethroid varroacides (Bayvarol® and Apistan®). This gave some breathing space until more was learned about the mites and their control. However, pyrethroid-resistant mites soon became apparent and by the autumn of 2001 resistant mites were found in Devon (less than 10 years after the use of these varroacides became widespread), introducing the need for the integrated pest management techniques that are most widely used now.

If bees show signs of virus, such as deformed wing virus, mite levels are high and it may be too late to save the colony – Photo: Claire Waring


One of the perverse advantages of varroa mite control is that if you get it wrong the bees will die. No hanging about being a bit sick. They just die – and often rather rapidly.

Under conditions of low mite infestation, varroa is frequently asymptomatic. A few mites will not do very much damage to a colony so it is very easy for an infestation to go unnoticed for a long time unless proper monitoring procedures are in place. Like many other honey bee diseases, if you don’t look for varroa you won’t find it – at least not until colonies start collapsing and this will not happen until mite numbers increase above a critical threshold level, which may vary from colony to colony.

At the point close to full colony collapse, the telltale signs of stunted wings and abdomens and visible mites on the adult bees or damaged brood in the combs become obvious. By this time, a range of viruses (and other diseases) are likely to have become well established in the colony doing much to hasten the speed of colony collapse.


Typically bees die of varroosis in the autumn among plentiful stores, or they may be found languishing in the spring, perhaps with just a handful of bees and the queen. Rarely are many dead bees seen as most of them will have left the colony for greener pastures (taking lots of mites with them to invade new colonies).

In the early days of varroa, beekeepers were often surprised that they could take off a heavy autumn honey crop from an apparently strong colony and yet within two or three weeks it was dead. It is helpful to remember that varroa treatment is best aimed at preserving winter bees in a healthy state so that uninfected young bees are able to survive over the long winter months.


It is a bad parasite that kills its host and many people believe it will be possible to breed strains of bees with greater resistance to varroa. Over the past 50 years much research work has been aimed at achieving this. Certainly some strains of bees are claimed to be varroa tolerant and there can be significant differences in infestation between colonies, even in the same apiary. This is an interesting topic but to consider it in sufficient depth will require yet another article.

By contrast, one of the more interesting ideas I have come across recently is that suggested by the American scientist, Thomas Seeley (2007). This research suggests that the mites are becoming less

virulent – maybe adapting more sympathetically to their host. This is thought to be due to lack of horizontal transmission of mites (that is hive-to-hive infestation) because of the remote location and the feral (unmanaged) mode of life of the bees. Thus only vertical transmission of mites occurs (that is transfer is only between parent and daughter stocks).

This offers a fascinating insight into host–parasite relationships and deserves more investigation as there are practical possibilities for beekeepers to utilise this information.


Varroa destructor is a very efficient killer of honey bees. It is a vector for viruses and other diseases and is now a serious fact of life for beekeepers in most places in the world, causing significant financial losses. It can only be controlled by a sensible and informed approach from the beekeeper. Proper monitoring and control is the current key to success.

The continuation of good research and the dissemination of practical beekeeping and control methods to other beekeepers are also essential if we are to maintain sustainable means of contemporary beekeeping.

Happy beekeeping.


Bailey L and Ball BV. 1991. Honey Bee Pathology (2nd ed). Academic Press, London.

Benjamin, A & McCallum, B. 2008. A World without Bees. Guardian Books, London, UK.

DEFRA/NBU (Morton J, Ball R, Brown M and Wilkins S). 2005. Managing Varroa. Central Science Laboratory, National Bee Unit.

Anderson, D & Trueman, JWH. 2000. ‘Varroa jacobsoni (Acari: Varroidae) is more than one species.’ Experimental & Applied Acarology, 24, 165–189.

Seeley, TD. 2007. Honey bees of the Arnot Forest: a population of feral colonies persisting with Varroa destructor in the north-eastern United States. Apidologie, 39; 19–29.

More information also available online at:

National Bee Unit indexVarroa.cfm

Bees for Development Information Portal id=49&p=30

New Zealand MAF Goodwin M & Van Eaton C. 2001. A Guide for New Zealand Beekeepers. New Zealand Ministry of Agriculture and Forestry, PO Box 2526, Wellington, New Zealand. This is available free online at: Problems/control-of-varroa-guide.pdf






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