By Alex Kirby
BBC News Online environment correspondent
French beekeepers say about 90 billion of their insects have been killed over the last 10 years by a pesticide.
Bees pollinate many crops
The chemical, used on crops including maize and sunflowers, damages the bees' sense of direction so they become lost.
It is used in the UK on several crops, though not in exactly the way it is used in France, and British beekeepers have been urged to be on their guard.
UK apiarists say the value of bees to the agricultural economy is immense, and they fear bees are becoming rarer.
The chemical implicated in the loss of French bees is imidacloprid, marketed under a variety of names including Gaucho.
It is slowly released in the plants, protecting them against insect attack by destroying their ability to find their way.
A London newspaper, the Observer, reported: "Almost immediately after the chemicals were introduced 10 years ago, beekeepers reported that their bees were becoming disoriented and dying.
Used in UK
"Within a few years honey production in south-west France fell by 60%. According to the chairman of the national beekeepers' association, Jean-Marie Sirvins, a third of the country's 1.5 million registered hives disappeared.
"As a result, France has had to import up to 24,000 tons of honey annually." The pesticide companies say their products are not responsible for killing the bees.
There are no reports of any ill effects from applications of imidacloprid in the UK, where it is licensed for use on beet.
French hives have been devastated
There are restrictions on its use when the plants are in flower, or for spraying the foliage.
But Richard Jones, the director of the International Bee Research Association, told BBC News Online: "Beekeepers here have to be on the alert.
"The varroa mite, which feeds on the bees' blood, arrived from mainland Europe, and we know that bees' nests can travel a long way on container ships.
"People hear about bees and think only about honey, but it's the other side of the problem that's worrying.
"They add billions of pounds to the value of the agricultural economy every year because of their work in pollinating crops like apples.
"We don't have enough bees in the UK, and we have very few feral bees. Every time a hedgerow is destroyed, that means the loss of nesting places for bumblebees."