Science: Invasion of the killer bees?

Scientists fear that imported bees from New Zealand carry a virus which could kill the native insect.

A buzz of anxious anticipation has descended on the rarefied world of British beekeeping. The Government is expected to rule within the next few weeks on whether to allow the import of several thousand worker bees from New Zealand. Some beekeepers believe the immigrants will revitalise British hives, but scientists are warning that they could introduce native honeybees to a deadly new disease.

The bees of New Zealand are noted for their docile nature - a definite plus for beekeepers - but almost all of them are infected with Kashmir bee virus (KBV). Although it causes few problems down under, experts in insect virology suspect that the virus could be lethal to British bees if it should ever gain a foothold here.

The Ministry of Agriculture, Fisheries and Food (Maff) now has to decide whether to give Geoffrey Munro, of Park Bee-keeping Supplies, permission to import the bees into the UK.

Before 1992, there were two or three other bee viruses in Britain which seemed to have no effect on the hives that were infected with them. Then came varroa, a tiny mite that feeds on bees and bee larvae in their honeycomb cells. The mites probably arrived as a result of beekeepers trading queens illicitly. The first few were found in the South-west, but since then they have travelled inexorably across the country and can now be found everywhere in England and Wales.

Varroa clings to adult bees and hitches rides from colony to colony, but in its normal host, the eastern (or Asian) hive bee, the mite is harmless - beekeepers find it, but there aren't many mites and the keepers certainly don't worry about them. However, when varroa jumps across to honeybees, it devastates hives.

To begin with, beekeepers thought it was the mite itself that damaged the developing bees. But the latest research by scientists at the Institute for Arable Crops Research in Rothamsted has shown that varroa is just a trigger for something far more sinister. Varroa alone has "no significant effect", says Dr Norman Carreck, of Rothamsted. It does not affect either the maturation of larvae into workers or the life span of those workers. But varroa can activate viruses that normally lie dormant in the bees and, once awoken, a virus can multiply, kill the entire hive and spread to other colonies.

There are still plenty of unknowns in the story. Not all bees carry viruses. Disease persists as an invisible infection in only a few individuals. "Something in the mite's saliva goes into the bee and interferes with its immune system, which allows the virus to multiply," Carreck explains. Active virus is then spread by varroa, often towards the end of the summer when there are many worker bees but not many larvae, so each bee has many mites biting it. As a result, hives fail to survive till spring, which is when the bees are most valuable to pollinate crops. This is why New Zealand enters the story.

New Zealand's autumn, when the hives are at their biggest and can easily be split, is our spring, when beekeepers, especially those who have lost hives to varroa-triggered disease, need new queens to establish new colonies. Thus there is a powerful economic incentive to import bees from New Zealand - exactly what Geoffrey Munro wants to do. Mr Munro acknowledges that New Zealand bees have KBV. But he insists that "it can't even be called a problem. It has no symptoms, no loss of bees, no real effect".

That is not the view of Dr Brenda Ball, senior scientist at Rothamsted. KBV "is the most virulent virus of bees known", she says. "Only about 100 particles of virus are required for infection and its rapid replication rate leads to death within three days."

Mr Munro points out that New Zealand maintains healthy colonies that show no signs of disease caused by KBV, but the essential difference is that New Zealand also lacks varroa.

"Before the arrival of varroa," Dr Ball says, two of the three bee viruses in Britain "had never been found to be responsible for bee mortality in nature". The danger is not that KBV will cause disease on its own, but that varroa will activate KBV and spread it through British hives. In the United States, where bees have varroa and KBV, scientists recently reported the first case of KBV killing a colony - which was also infested by varroa.

Maff has asked interested parties to comment on Mr Munro's application to import packages of New Zealand bees. Dr Ball has told Maff bluntly that "it would be undesirable to risk" the introduction of KBV. Mr Munro says KBV will "cause no practical or scientific problem at all." The ministry has also asked for a risk assessment from its National Bee Unit in York, despite having been told by a more extensive study it commissioned in 1989 "that the importation of... bees from New Zealand poses a real risk of also importing KBV".

Mr Munro claims that a UK ban on imports of bees from New Zealand would fall foul of the World Trade Organisation. But within the General Agreement on Tariffs and Trade (Gatt) there is an agreement that allows a country to restrict trade to safeguard human, animal or plant health, although not to protect domestic agriculture from imports. Ironically, it is just such restrictions on trade that have enabled New Zealand to build up its healthy honeybee industry; no live bees have been allowed into New Zealand for the past 40 years.

The UK needs to import New Zealand bees to replace colonies that have died, but Dr Ball reckons that is not a good enough reason to run the risk of introducing a disease new to Britain. She points out that when it first arrived, varroa did kill many colonies, but as beekeepers learned to mitigate its effects and control the infection, losses declined. Today, it is manageable. A few beekeepers, however, seem to regard stocks as expendable. They would prefer to buy in replacements rather than improve their husbandry, even though those imports threaten beekeepers who take care to look after their hives.

Adrian Waring, general secretary of the British Bee-Keepers Association, says that the vast bulk of British beekeepers want nothing to do with New Zealand queens. He has no great confidence in Maff's ability to protect British bees, but whether Maff or beekeepers are more to blame is anybody's guess. When varroa turned up in April 1992, the ministry created a Statutory Infected Area, supposed to restrict the movement of infected bees. Though they told the beekeepers, they couldn't tell the bees, and each year the area has had to be enlarged. By 1997, it covered the whole of England and Wales.

Maff now has a chance to prevent the entry of KBV, but Waring is not optimistic.

"Ten thousand of my members versus a single request from an individual," he says. "You'd have thought by now that we would have learnt a bit of a lesson."