Bayer and Syngenta criticised for secrecy after unpublished research obtained under freedom of information law linked high doses of their products to damage to the health of bee colonies

Unpublished field trials by pesticide manufacturers show their products cause serious harm to honeybees at high levels, leading to calls from senior scientists for the companies to end the secrecy which cloaks much of their research.

The research, conducted by Syngenta and Bayer on their neonicotinoid insecticides, were submitted to the US Environmental Protection Agency and obtained by Greenpeace after a freedom of information request.

Neonicotinoids are the world’s most widely used insecticides and there is clear scientific evidence that they harm bees at the levels found in fields, though only a little to date showing the pesticides harm the overall performance of colonies. Neonicotinoids were banned from use on flowering crops in the EU in 2013, despite UK opposition.

Bees and other insects are vital for pollinating three-quarters of the world’s food crops but have been in significant decline, due to the loss of flower-rich habitats, disease and the use of pesticides.

The newly revealed studies show Syngenta’s thiamethoxam and Bayer’s clothianidin seriously harmed colonies at high doses, but did not find significant effects below concentrations of 50 parts per billion (ppb) and 40ppb respectively. Such levels can sometimes be found in fields but concentrations are usually below 10ppb.

However, scientists said all such research should be made public. “Given all the debate about this subject, it is hard to see why the companies don’t make these kinds of studies available,” said Prof Dave Goulson, at the University of Sussex. “It does seem a little shady to do this kind of field study - the very studies the companies say are the most important ones - and then not tell people what they find.”

Prof Christian Krupke, at Purdue University in Indiana, said: “Bayer and Syngenta’s commitment to pollinator health should include publishing these data. This work presents a rich dataset that could greatly benefit the many publicly funded scientists examining the issue worldwide, including avoiding costly and unnecessary duplication of research.”

Ben Stewart, at Greenpeace, said: “If Bayer and Syngenta cared about the future of our pollinators, they would have made the findings public. Instead, they kept quiet about them for months and carried on downplaying nearly every study that questioned the safety of their products. It’s time for these companies to come clean about what they really know.”

Syngenta had told Greenpeace in August that “none of the studies Syngenta has undertaken or commissioned for use by regulatory agencies have shown damages to the health of bee colonies”. Goulson said: “That clearly contradicts their own study.”

Scientists also noted that the companies have been previously been critical of the research methods they themselves used in the new studies, in which bees live in fields but are fed sucrose dosed with neonicotinoids.

In April 2016, in response to an independent study, Syngenta said: “It is important to note that the colony studies were conducted by directly feeding colonies with spiked sucrose, which is not representative of normal field conditions.”

In 2014, commenting on another independent study, Bayer told the Guardian the bees “are essentially force-fed relatively high levels of the pesticide in sugar solutions, rather than allowing them to forage on plants treated with” pesticide.

“If someone had done this type of study and found harm at more realistic levels, the industry would have immediately dismissed it as a rubbish study because it was not what happens naturally to bees,” said Goulson. “So it is interesting that they are doing those kinds of studies themselves and then keeping them quiet.”

Utz Klages, a spokesman for Bayer, said: “The study [Bayer] conducted is an artificial feeding study that intentionally exaggerates the exposure potential because it is designed to calculate a ‘no-effect’ concentration for clothianidin. Although the colony was artificially provided with a spiked sugar solution, the bees were allowed to forage freely in the environment, so there is less stress - which can be a contributing variable - than if they were completely confined to cages. Based on these results, we believe the data support the establishment of a no-effect concentration of 20ppb for clothianidin.”

He said a public presentation would be made at the International Congress of Entomology next week in which the new results would be discussed.

Two of the world's top three insecticides harm bumblebees – study Read more

A spokesman for Syngenta said: “A sucrose-based mechanism was used on the basis that it was required to expose bees artificially to thiamethoxam to determine what actual level of residue would exert a toxic effect.”

Given the lower concentration usually found in fields, he said: “The reported ‘no adverse effect level’ of 50ppb indicates that honey bee colonies are at low risk from exposure to thiamethoxam in pollen and nectar of seed treated crops. This research is already in the process of being published in a forthcoming journal and is clearly already publicly available through the FOI process in the US.”

Matt Shardlow, chief executive of conservation charity Buglife, said: “These studies may not show an impact on honeybee health [at low levels], but then the studies are not realistic. The bees were not exposed to the neonics that we know are in planting dust, water drunk by bees and wildflowers, wherever neonics are used as seed treatments. This secret evidence highlights the profound weakness of regulatory tests.”

Researchers also note that pollinators in real environments are continually exposed to cocktails of many pesticides, rather than single chemicals for relatively short periods as in regulatory tests.