A major 18-year study has found evidence linking controversial "neonicotinoid" pesticides with “large-scale population extinctions” of wild bees for the first time.

The insecticides have been shown to have “sub-lethal” effects on bees, which are vital pollinators for many crops, in laboratory-style conditions and small-scale studies.

But their actual effect in the real world was not well understood – until now.

The use of neonicotinoids has been restricted by the European Union and banned in some places, such as the US state of Maryland, because of growing concern about their effects on bees.

Last month the UK Government refused an application to use the pesticide – by the National Farmers Union – for the second time this year, although it has previously approved its use. However campaigners fear the restrictions will be lifted after the UK leaves the EU.

The study looked at nearly 32,000 surveys of 62 wild bee species that were carried out across much of England between 1994 and 2011 inclusive.

The researchers examined the effect of the first widespread use of neonicotinoids as a treatment on oilseed rape seeds in 2002. This was mainly designed to protect the crop from another insect, the cabbage stem flea beetle.

But, writing in the journal Nature, the researchers concluded: “Our results provide the first evidence that sub-lethal impacts of neonicotinoid exposure can be linked to large-scale population extinctions of wild bee species, with these effects being strongest for species that are known to forage on oilseed rape crops.”

The researchers divided the countryside into five-kilometre squares, which they classed as a “population” of bees, and looked at how they changed over time.

Wild bees have suffered a general decline in recent years, but the study found that this was three times worse for species that regularly feed on oilseed rape, such as the buff-tailed bumblebee, compared to those that forage on various different flowers.

For five species investigated, including the spined mason bee and the furrow bee, the study found neonicotinoid use was linked to at least 20 per cent of local population extinctions of wild bees.

The number of populations of the worst affected species, the sharp collared furrow bee, fell by 45 per cent between 1994 and 2011 with the researchers estimating 31 percentage points of the decline was linked to neonicotinoids and 14 points to other causes.

The researchers said the extinctions they referred to were local ones near to oilseed rape fields, rather than extinctions across England as a whole.

The lead author of the Nature Communications paper, Dr Ben Woodcock of the Centre for Ecology and Hydrology, said: “As a flowering crop, oilseed rape is beneficial for pollinating insects.

“This benefit however, appears to be more than nullified by the effect of neonicotinoid seed treatment on a range of wild bee species.

“Although we find evidence to show that neonicotinoid use is a contributory factor leading to wild bee species population decline, it is unlikely that they are acting in isolation of other environmental pressures.

“Wild bees have undergone global declines that have been linked to habitat loss and fragmentation, pathogens, climate change and other insecticides.”

Animals in decline Show all 8 1 /8 Animals in decline Animals in decline Harbour seal (Phoca vitulina) Where: Orkney Islands. What: Between 2001-2006, numbers in Orkney declined by 40 per cent. Why: epidemics of the phocine distemper virus are thought to have caused major declines, but the killing of seals in the Moray Firth to protect salmon farms may have an impact. Alamy Animals in decline African lion (Panthera leo) Where: Ghana. What: In Ghana’s Mole National Park, lion numbers have declined by more than 90 per cent in 40 years. Why: local conflicts are thought to have contributed to the slaughter of lions and are a worrying example of the status of the animal in Western and Central Africa. Animals in decline Leatherback turtle (Dermochelys coriacea) Where: Indonesia, Malaysia, Mexico, Costa Rica. What: Numbers are down in both the Atlantic and Pacific. It declined by 95 per cent between 1989-2002 in Costa Rica. Why: mainly due to them being caught as bycatch, but they’ve also been affected by local developments. Alamy Animals in decline Wandering albatross (Diomedea exulans) Where: South Atlantic. What: A rapid decline. One population, from Bird Island, South Georgia, declined by 50 per cent between 1972-2010, according to the British Antarctic Survey. Why: being caught in various commercial longline fisheries. Alamy Animals in decline Saiga Antelope (Saiga tatarica) Where: Kazakhstan, Mongolia, Russia, Turkmenistan, Uzbekistan. What: fall in populations has been dramatic. In the early 1990s numbers were over a million, but are now estimated to be around 50,000. Why: the break up of the former USSR led to uncontrolled hunting. Increased rural poverty means the species is hunted for its meat Animals in decline Swordfish (Xiphias gladius) Where: found worldwide in tropical, subtropical and temperate seas. Why: at risk from overfishing and as a target in recreational fishing. A significant number of swordfish are also caught by illegal driftnet fisheries in the Mediterranean Animals in decline Argali Sheep (Ovis mammon) Where: Central and Southern Asian mountains,usually at 3,000-5,000 metres altitude. Why: domesticated herds of sheep competing for grazing grounds. Over-hunting and poaching. Animals in decline Humphead Wrasse (Cheilinus undulatus) Where: the Indo-Pacific, from the Red Sea to South Africa and to the Tuamoto Islands (Polynesia), north to the Ryukyu Islands (south-west Japan), and south to New Caledonia. Why: Illegal, Unregulated and Unreported (IUU) fishing and trading of the species

Paul de Zylva, nature campaigner at Friends of the Earth, said the study “adds a huge new peak to the existing mountain of evidence showing the risk these chemicals pose to our bees”.

“This is the strongest ever evidence of harm to bees from neonicotinoid pesticides in British fields,” he said.

“If the government genuinely wants to safeguard Britain’s bees, it must keep the ban on neonicotinoid pesticides regardless of what happens with Brexit – and tighten the way pesticides are tested and licensed for use.”

However the NFU insisted farmers had to use neonicotinoids or something similar.

Dr Chris Hartfield, the NFU’s “bee health specialist”, said: “This study is another interesting piece to an unsolved puzzle about how neonicotinoid seed treatments affect bees.

“It does not show that neonicotinoids are causing widespread declines in pollinator populations and it certainly does not show that neonicotinoid use has caused any extinction of bees in England.”

He added that without many “plant protection products” farmers’ ability “to produce wholesome, affordable food for the nation will continue to stagnate”.

“While this study claims to provide an important contribution to the evidence base underpinning the current EU moratorium on some uses of neonicotinoids, experts reviewing all the evidence have concluded that there are still major gaps in our knowledge and a limited evidence base to guide policymakers,” Dr Hartfield said.

Neonicotinoids are a class of pesticides that are similar to nicotine.

And Nick Mole, of the Pesticide Action Network UK, said the current debate was similar to the situation in the 1950s when the tobacco industry attempted to deny that smoking harmed human health.

“How much more proof, more evidence, does the NFU need? Are they waiting until there are no more bees?” he said.