It is a sad fact of life that when something is in short supply its price rockets - and then the thieves move in. The big rise in the number of beehives being stolen over the past few months is a sharp economic reminder of the colony losses beekeepers have experienced over the past few years.

It is an issue growers are being asked to confront on more than one level: even if you do not rely on honeybee pollinators for your crops, the habitats around your farm or orchard and your use of crop-protection chemicals are implicated as potential causes of the problem.

"Thefts of beehives have always been with us to a small extent," says John Howat, secretary of the Bee Farmers' Association, which represents the 200 to 300 large-scale commercial beekeepers who make their living from pollination services and honey production.

"But this year is worse. Honeybees are in short supply, but because of all the publicity about losses, far more people wish to keep bees. The law of supply and demand has tripled the cost of a colony of bees this year."

The worst theft so far was 18 hives from a single site in Shropshire.

Defra says the past two years have seen recorded losses of between 10 and 15 per cent in honeybee numbers. But it points out that, because beekeeping is dominated by about 33,000 amateur or semi-amateur beekeepers, many of whom are not members of recognised groups, accurate figures are hard to come by. The true losses are probably much higher.

"Among professional beekeepers, winter losses - colonies dying between October or November and March or April - have traditionally averaged three to five per cent," says Howat.

Over the winter of 2007/08, that increased to 15 per cent. Last winter, it averaged 12.5 per cent, but among individual beekeepers it could vary between zero and 40 per cent.

Colony loss is not just a UK problem. Similar diminishing levels have been reported across Europe, while beekeepers in the US are facing even greater losses due to the phenomenon known as "colony collapse disorder".

Honeybees are essentially a domesticated animal, say professional beekeepers. Research in the 1990s by senior technician Norman Carreck and colleagues at the University of Sussex's Laboratory of Apiculture & Social Insects showed that 17 different EU crops depend on insect-pollinator services, including tree fruit, soft fruit and runner beans.

"Insect pollination contributes seven per cent of the value of the 30 most widely grown insect-pollinated crops, and 85 per cent of that is due to honeybees," says Carreck.

British beekeepers, and most bee researchers and advisers, believe the recent spate of losses has been caused primarily by pests and disease, and exacerbated by a run of unseasonable summer and winter weather.

"In my view, the root cause is the Varroa mite," says Howat. "This weakens the bees, spreads viruses, reduces their immune systems and makes them vulnerable to anything else going.

"On top of that, the very poor summers of 2007 and 2008 resulted in 'poorer-quality' bees because mating was disrupted."

It looks more promising for 2009, however. "So far we have not seen any effects on pollination this year, which is good because if losses had continued at the same rate as last year we could have done," says NFU horticulture adviser Chris Hartfield.

"At present, it appears bees have come through the winter well." He suggests that last year's heavy losses made beekeepers particularly vigilant about the health of their colonies, so bees went into the winter in better condition.

Mike Brown, head of Defra's National Bee Unit, believes one of the causes of the UK's bee health problems is the development in Varroa mites of resistance to pyrethroids used to treat infested colonies. "We haven't found anything mysterious like the colony collapse disorder in the US," he says. "Our bee inspectors have always found rational explanations for bee losses reported here."

Industrial-scale operations

Many beekeeping businesses in the US manage large numbers of colonies, and it is in these that bee inspectors have found most cases of the disorder. As Brown explains, "industrial" bees are worked hard and fed cheap sugars, suggesting that overworking colonies might be a factor.

While bee experts blame pests and diseases for the UK's honeybee problems, it is the possible role of pesticides that has received most public attention, despite the fact that there has been no confirmed incident of honeybee poisoning caused by the approved use of an agricultural pesticide in the UK since 2003.

In April this year, the Soil Association condemned Defra for not banning "pesticides that kill honeybees" and accused the Government of "ignoring scientific evidence". The association is particularly concerned about neonicotinoids, and in particular imidacloprid used as a seed treatment, following reports that it was implicated in widespread bee deaths in Europe.

The most widely publicised cases were heavy bee colony losses in Germany and Slovenia last spring, where the neonicotinoid clothianidin was used as a seed dressing on maize as compulsory treatment for the notifiable pest western corn cutworm. It appears that a fault involving a binding agent during the coating process meant the pesticide did not stick well enough to the seed. When the seed was sown with pneumatic drills, a dust of the compound was blown onto surrounding plants, where bees were foraging. Germany withdrew the use of clothianidin while this was investigated, but the ban is now lifted.

Despite regular tests, there have been no confirmed cases of bee poisoning from imidacloprid in the UK. In France, its use on sunflower crops has been blamed for colony losses and led to a ban. Approval as a treatment for maize seed has also been withdrawn. Despite that, colony loss has continued there, says Carreck.

The Soil Association claims bees are more susceptible to pesticide poisoning than other insects because they are less able to break them down, so are more likely to be affected by sub-lethal exposure. It cites French research (by the national research institute INRA) that found imidacloprid at doses as low as 6ppb could impair bee behaviour.

But Carreck says the scientific consensus is that the recent losses in France were caused by a combination of other factors, and by pyrethroid-resistant Varroa in particular.

He adds: "You can't rule out a more subtle sub-lethal effect of imidacloprid, perhaps in conjunction with other factors such as disease. And work is underway to look at possible toxic effects of breakdown products of this substance in bees."

Pesticide backlash

Meanwhile, retailers have reacted. The Co-op, for example, has temporarily prohibited neonicotinoid use on its own-brand fresh produce. Imidacloprid has a specific off-label approval for seed treatment of lettuce and a number of brassicas, but these are harvested before ever reaching the flowering stage. "Oilseed rape is probably more of a concern than any horticultural crops," says Carreck.

"With at least 600,000ha grown per year it is one of the major nectar sources for UK beekeepers. It remains the greatest potential threat to honeybees from insecticides should the (crop protection) products being used change."

He points out that although biological controls are being developed for a range of crops, including oilseed rape, we should not assume all such agents are safe to bees. "Some are harmful and protocols for testing are in their infancy," he points out.

There is much that growers can do to help beekeepers improve bee health, says Howat. "Plant field margins and conservation areas with a seed mix of bee-friendly plants," he says. "And be very careful with sprays when flowers are in bloom - although from personal experience I know that orchard managers and farmers are already well aware of this and work closely with me if and when spraying is required."

Bean growers Paul and Mike Southall of Norchard Farm, Worcestershire - a business that was highly commended at the Grower of the Year Awards last year - are among the 500 farmers and growers who have taken part in Operation Bumblebee, a scheme run by Syngenta to establish specially designed bee habitats with a mix of flowering plants on farms across the UK.

"The results we have seen have been incredibly exciting," says Mike Southall. "The speed at which bumblebees and other insects have colonised even small areas of dedicated habitat is quite remarkable." Syngenta says more than 1,000ha have been planted and it is extending the scheme into Europe.

Hartfield calls for better liaison between growers and beekeepers, not just to keep beekeepers informed about spray programmes but so that farmers and growers can offer more hive sites.

"It's not just about getting hives in to pollinate the crop. More hive sites would encourage beekeepers to maintain more colonies, and growers are well placed to offer good habitats, access and security."

The National Bee Unit is developing a sophisticated database - the Beebase - and is inviting professional and amateur beekeepers to supply their details. This will not only allow it to target more beekeepers with advice on colony health but could also encourage liaison between growers and beekeepers.

The Biotechnology & Biological Sciences Research Council, Defra, the Natural Environment Research Council, the Scottish Government and the Wellcome Trust have put together £10m to fund R&D to improve bee health and will call for project proposals at a meeting next month.

"It is vital that the bulk of the new funding is used on projects that focus on honeybees, as they are responsible for 85 per cent of crop pollination," Hartfield points out.

Assault on Varroa

Defra-funded studies conducted at Warwick HRI and Rothamsted Research have found potential biological control agents that could be used against Varroa mites.

"We examined 50 different kinds of fungi that attack insects, looking for any that would kill Varroa mites without affecting bees," said Warwick HRI's Dave Chandler (pictured).

"They also need to work in the warm, dry conditions of a beehive. We have found four fungi that could meet these requirements."

The next stage of the work is to look at the effectiveness of the chosen species and how they can be applied in practice.

Among the methods being considered is a "fungal footbath", which the bees must pass through on their way into the hive.

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