A major £2.7m study into a controversial type of nicotine-based pesticide has found it can cause harm to bees, prompting environmentalists and some scientists to call for an outright ban.

Funded by two major agrochemical companies, the researchers discovered neonicotinoids were associated with negative effects on bees at sites in the UK and Hungary. However, they also found it had some “positive” effects on bees in Germany.

Nevertheless, writing in the leading journal Science, they concluded that the chemicals reduced the ability of bees to establish new populations the following year with a 24 per cent reduction in the Hungarian populations.

Neonics, as they are known, are already the subject of a partial ban by the European Union, which is considering preventing their use completely.

Other studies have reached similar conclusions but there were claims that these were either too small-scale or had not been carried out in ‘real world’ conditions. The latest study was designed to put an end to the debate once and for all.

The Soil Association said the findings were the “final, fatal blow” to the idea that neonics were safe for bees. And one leading bee researcher, Professor Nigel Raine, of Guelph University, said that the overall message from the study was that the pesticides had “appreciable negative impacts”.

Syngenta, which provided some of the funding along with Bayer Cropscience, noted the researchers had found the “direct mortality effects” were “likely to be rare” and highlighted the “positive and beneficial impact” for bees at the German sites.

But it added that the study had also helped to identify issues that could be addressed to “improve agriculture productivity while taking care of the environment”.

Writing in Science, researchers said: “For honey bees, we found both negative (Hungary and United Kingdom) and positive (Germany) effects during crop flowering.

“In Hungary, negative effects on honey bees, associated with clothianidin [a type of neonic], persisted over winter and resulted in smaller colonies in the following spring (24 per cent declines).

“In wild bees, reproduction was negatively correlated with neonicotinoid residues. These findings point to neonicotinoids causing a reduced capacity of bee species to establish new populations in the year following exposure.”

Two leading bee scientists, who were not involved in the study, agreed that it showed neonics were damaging bees.

Professor David Goulson of Sussex University, said: “This is by far the largest field trial ever conducted on the impacts of neonicotinoids on bees. Exposure of bees was entirely field-realistic; indeed, farmers simply followed normal farming practice.

“The findings are in agreement with a number of earlier studies: field exposure to neonicotinoids has clear negative impacts on bumblebees and solitary bees.

“Effects on honeybees were also predominantly negative but more variable. Interestingly, analysis of residues of neonicotinoids in bee nests suggests that much bee exposure was not from the treated crop adjacent to the colony but was coming from other sources in the landscape, suggesting widespread contamination of the environment.

“In the light of this new study, continuing to claim that use of neonicotinoids in farming does not harm bees is no longer a tenable position.”

Professor Raine said the “long-awaited paper” revealed “varying impacts” of neonicotinoid exposure.

But he added: “The overall picture points towards appreciable negative impacts on these important pollinators across the time course of this study.

“It is concerning that bumblebee colonies produce fewer queens, and solitary bees (Osmia bicornis) produce fewer offspring, where higher levels of exposure to neonicotinoids were found.

“These bees represent the basis for the next generation of these species in the following year, and fewer of these important individuals could have significant impacts on population size and persistence.”

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

However Professor Lin Field, head of the Department of Biological Chemistry and Crop Protection at Rothamsted Research, said the results were “very mixed”.

“Overall most of the parameters tested show no significant differences and for those that do there are sometimes conflicting results, meaning that it is hard to draw any conclusions,” she said. “My feeling is that no firm conclusions can be drawn from these results.”

Environmental groups called for the EU ban to be extended to all crops.

Vito Buonsante, a legal expert at ClientEarth, said: “The fact that Bayer and Syngenta were involved in one of the studies will make it much harder for industry to trot out the traditional argument that the results can't be trusted as the methodology was wrong. This is yet more evidence that the EU should adopt a total ban on these chemicals.

“Bees and wild pollinators are fundamental to our food supply, and we know neonicotinoids are threatening their existence. To let companies keep selling them, and farmers keep spraying them, would cause irreversible harm to the planet.”

Sandra Bell, a Friends of the Earth nature campaigner, said the study showed neonics came with “a nasty sting in the tail for our under-pressure bees”.

“It’s time for a complete and permanent ban on these chemicals,” she said. “We can successfully grow crops without neonicotinoids, and without resorting to more pesticides. The UK government must now do more to help farmers grow the crops we need without harming Britain’s bees.”

And Louise Payton, a Soil Association policy officer, said: “This should now be the final, fatal blow to neonicotinoids.

“With neonics widely polluting farms, and with UK farmers still treating most wheat, an outright ban is needed immediately.”

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In a statement, Syngenta sounded a positive note about the results of the study, led by experts at the UK’s Centre for Ecology and Hydrology (CEH), but said it would seek to make improvements to their products.

Dr Peter Campbell, the company’s head of research collaborations, said: “We welcome the fact that the study concludes that ‘neonicotinoid residues were detected infrequently... [and] direct mortality effects by exposure to high concentrations of neonicotinoids are likely to be rare’.

“We were also pleased to see that in Germany during crop flowering, the use of neonicotinoid seed treatments has a positive and beneficial impact for both honeybees and bumblebees.”

The firm said other factors, such as beekeeping practices and planting wild flowers on field margins, could mean the impact of neonics was “minimal or in some cases even positive”.

Dr Campbell added: “Syngenta is absolutely committed to improving bee health as bees are critical for the sustainability of agriculture and our business.