Short-haired bumblebees were due to be flown from New Zealand and re-introduced to Britain to tackle pollination crisis

An "international rescue mission" to tackle Britain's pollination crisis has suffered a setback after a shipment of bees due to be imported into the country died just days before their release.

Natural England, the government's countryside agency, chose the short-haired bumblebees from New Zealand because they were originally from the UK, but have since become extinct in their homeland.

But less than two weeks before the selected bees were due to be flown over and released on Friday, scientists say they have died in hibernation.

The setback is an example of the problem conservationists are increasingly warning of: that once a species has been destroyed in its local habitat, it is very hard to restore it - a strategy they fear many rely on when they are pushing through developments and other threats to biodiversity.

However, Natural England said the deaths would only delay the re-introduction project, which is now planned for next summer, and they were confident it would eventually succeed.

"An expedition to New Zealand will take place this November to collect queen [bees] to rear, and the next generation of queens will be returned to the UK the same time next year for release," said a statement from the agency. "Over the next six months, work will concentrate on creating more habitat for bumblebees, perfecting the rearing technique in New Zealand and raising the profile of the importance of bumblebees with local communities. This is a long-term project and we hope for many future releases."

The short-haired bumblebees were transported to New Zealand in the first refrigerated lamb ships in the late 19th century, to pollinate crops of red clover to help new emigrant farmers. They have clung on in small numbers, but are unprotected and under threat.

The plan to bring them back to the UK, where they were declared extinct in 2000, was in response to a steep decline in bumblebees and other pollinating insects in recent years, a problem blamed on the loss of most wildflowers in Britain's intensively farmed landscapes - some of which were also transported to New Zealand and have survived in the South Island's England-like climate.

To prepare for the bees' return, Natural England worked with farmers in Kent to make more than 550 hectares of land suitable for the bees, as well as nesting birds, mammals and invertebrates.

"This international rescue mission has two aims – to restore habitat in England, thereby giving existing bees a boost; and to bring the short-haired bumblebee home where it can be protected," said Poul Christensen, Natural England's chairman, when the project was announced last year [2009]. "Bumblebees are suffering unprecedented international declines and drastic action is required to aid their recovery. Bumblebees play a key role in maintaining food supplies - we rely on their ability to pollinate crops and we have to do all we can to provide suitable habitat and to sustain the diversity of bee species."