A third of British wild bees and hoverflies are in decline, according to a new study.
The study found "winners
Scientists warn. "and" losers "among hundreds of wild bees and hoverflies.
Common species are being lost at the expense of rare ones
- Five key things about the extinction crisis
The study looked at trends in 353 wild bees and hoverflies in Scotland, England and Wales over 33 years from 1980.
A third of the species experienced declines in terms of areas where they were found, while about 10% became more abundant, including bees that pollinate flowering crops, such as oil seed rape.
While some pollination is carried out by honeybees in hives, much of the pollination of crops and wild plants is carried out by their wild relatives and other insects, especially hoverflies.
Dr Gary Powney of the Center for Ecology and Hydrology (CEH) in Wallingford, Oxfordshire, said during the increase in key crop pollinators is "good news", species have declined overall.
"It would be
"If anything happens to them in the future, there will be other species to step up and fulfill the essential role of crop pollination. "
The Losses were concentrated among the rare, specialized species. Dr Nick Isaac, of the Center for Ecology and Hydrology (CEH) in Wallingford, Oxfordshire, said this was "particularly bad news if you're interested in wildlife and conservation."
The "losers" include solitary bees, which live in burrows in the ground, and upland, living on mountains and moorlands. Among the "winners" are 22 of the most important crop pollinators.
Experts say the increase in some common species is set against a background of an overall loss of diversity.
"Every square kilometer in the UK has lost an average of 11 species of bee and hoverfly, between 1980 and 2013, according to the new analysis," said Dr Lynn Dicks of the University of East Anglia.
She said the pattern of biodiversity loss is happening everywhere we look.
- New order of insects sets up in the UK
- Cricket's summer song making a comeback
- 100 new insect species discovered
Matt Shardlow, chief executive of the charity Buglife, said the pollinators are in trouble and that the health of our environment and food supply
"Solitary bees, rare bees and bees and hoverflies that are live in the uplands are in particular trouble and urgent need help," he said.
The research is based on an analysis of more than 700,000
What does it mean?
What does it mean? ing the decline?
The scientists think habitat loss is likely key. Other possible factors include climate change – which could be due to impact on upland and northern species.
They say the relative success of some species could be put into place by farmers, such as sowing wildflower strips.  Or this might be because much more oilseed rape is grown now than in 1980.
Another factor is the use of insecticides.
In 2013, the European Union introduced a temporary ban on the widespread use of insecticides known as neonicotinoids in light of evidence
The researchers say.  The researchers say
They are continuing to call for pollinating insects.
The loss of insects has far-reaching consequences for entire ecosystems.
A recent scientific review of insect numbers in the world that said 40% of species were undergoing "dramatic rates of decline" , with bees, ants and beetles disappearing eight times faster than mammals, birds or reptiles.
Previous studies have found losses of butterflies, moths, beetles, bees and hoverflies across the UK.
The study is published in the journal Nature Communications.
Follow Helen on Twitter .