The honeybee and the varroa mite

The honeybee varroa mite (not actual size!) has killed millions of honeybees worldwide

Varroa mites have killed millions of honeybees across the world. Dr Stephen Martin , a University of Sheffield expert on the varroa mite, spoke to BBC Radio Sheffield in August 2010.

In the 1950s the varroa mite jumped species from the Eastern (Asian) Honeybee to the species we have in England - the Western (African) Honeybee. Since then, the varroa mite and its associated diseases have been a major factor in the decline of honeybee populations worldwide, alongside a loss of wildflower habitats, the use of pesticides and recent poor summers.

"The varroa mite looks like a brown crab and is large in comparison to the honeybee - about 2mm long," said Dr Martin. "It's like us humans having a small monkey on our back all the time!"

The varroa mite can live on the back of an adult bee for two years. In Winter it feeds off the bee's blood, and in Summer it sneaks into the developing brood and reproduces.

"It doesn't kill the bees straight off but it passes disease and viruses which shorten the bee's lifespan," explains Dr Martin. "The colonies then collapse during Winter."

The varroa mite has been transported to every country in the world, except Australia, on the backs of honeybees.

What can be done?

Beekeepers use various methods to control the mite. A non-chemical method is to remove drone bees (which the varroa mites love to live on) from the colony but Dr Martin says the most effective method has been a synthetic chemical compound, based on Chrysanthemum flowers.

"It's basically a poison - a neurotoxin," says Dr Martin. "The mites are small in relation to the bee so you can give the right dose to kill the mite but not the bee. It's been very effective for 10 years but now the mites have become resistant to it so they're starting a whole new bunch of pesticide."

Just 2000 varroa mites can kill a colony of 30,000 honeybees.

"Often the bees disband before they die, known as a colony collapse," says Dr Martin. "The bees get disorientated and drift off into other colonies, taking the mites with them."

Trying to remove a Killer Bee hive in Mexico City, 1995

Honeybees are worth about £200m a year to British agriculture and it is only because they are so economically important to man that they haven't been allowed to be wiped out altogether.

"If we had left the problem, we would probably have lost the bees," says Dr Martin. "There is a school of thought that eventually natural selection would choose the bees that can survive the varroa mites. This was tried on a Swedish island and there is now a very small population of very small colonies that have to swarm all the time, but most of our bees would have died if we had left them.

"They did nothing in Czechoslovakia and lost literally a million colonies. Eventually the beekeepers stepped in."

Killer bees

A very aggressive honeybee which is deadly to humans and animals is resistant to the varroa mite.

The Killer Bee was bred in South America, as Dr Martin explains:

"Killer Bees are the result of an experiment to bring together two sub-species of bees - the European and the Southern African honeybees - which should not have been brought together.

"The result is a very aggressive bee which has moved from South American to the United States, killing people and cattle. They do have varroa mites but, for some reason that we don't fully understand, they're resistant to them.

"So now places like Mexico and Brazil don't need to use pesticides and can sell organic honey at a higher price. Man has created a problem and solved it at the same time."

Longshaw bees

The BBC Bee Part of It beehives at the Longshaw Estate passed their first inspection in July 2010

The BBC Radio Sheffield honeybees at the Longshaw Estate were given a clean bill of health, free from varroa mite , in July 2010.

But Dr Martin says that doesn't mean there are no varroa mites at all in the hive: "I can guarantee there are varroa mites, but at such low levels that they won't cause a problem. There may be only tens of them but if we stop controlling the mites they build up and in a couple of years we will lose the colony."

Find out more about how you can help honeybees with the BBC Bee Part Of It project.