We're only going to get rid of mites when we find a biological control for them

Richard Jones, IBRA

Once it has infiltrated a colony, the parasite proliferates by feeding on immature bees, making them susceptible to other infections and shortening their lifespan.

The mite is small on a human scale, but to a bee is as big as a dinner plate is to a 1.8-metre-tall human.

Typically, beekeepers use chemicals containing active ingredients known as pyrethroids to control the numbers of mites in their hives. The treatments are only supposed to be administered for up to six weeks at a time, to limit the chance that the mites will develop resistance.

Control group

However, some beekeepers in Devon are suspected of leaving the plastic strips impregnated with the treatments in hives for months at a time.

Richard Jones, director of the International Bee Research Association (IBRA), said it was inevitable that resistant mites would appear eventually in the UK because they had been found on the continent for many years before now.

He said if the chemical strips were left in hives the dose of lethal chemical they contained was diluted and led to mite populations that could survive its effects.

The resistant mites were likely to spread as slowly as Varroa did after 1992, when it was first discovered in Devon, said Mr Jones.

But the picture could be complicated if other beekeepers prove as lax with the treatments as some Devon apiarists.

National programme

Scientists suspect that the resistant mites have been extant in Devon for a couple of years. The resistant population was discovered in a spot check carried out by a regional bee inspector.

Mr Jones said the hope was that the resistant mites spread slowly enough throughout the rest of the country to give scientists time to develop alternative treatments.

"We're only going to get rid of mites when we find a biological control for them rather than any pharmaceutical product," he said. Current promising lines of research involve funguses and pheromone traps.

A spokeswoman for the Department for Environment, Food and Rural Affairs, said a monitoring scheme had been set up to log the spread of the pyrethroid-resistant mites.

The National Bee Unit is also giving beekeepers advice about ways to test if their hives are infested with the resistant mites.