Production of many field crops including vegetables is at risk if neonicotinoid pesticides are more widely restricted or banned completely, Rothamsted Research argues in a position statement published this week.
"Furthermore, if groups of chemistries are limited by legislation, the remaining groups will be more widely used, resulting in an increased risk of pests developing resistance to them," it adds.
The institute's concern follows draft proposals by the EU to replace its temporary restriction on the use of three neonicotinoids on flowering crops with a widespread ban across Europe, potentially covering all field crops, not just flowering ones.
Rothamsted says it "laments the lack of evidence for the pesticide restrictions" and reiterates its 2014 call for "a proper science-led risk assessment to ... help us balance the risks and benefits for crop protection, crop pollination, ecosystem function and our health appropriately".
The NFU is urging farmers and growers to make political representatives aware of the "devastating" results of a blanket neonicotinoid ban on outdoor crops. The union has written to the European Commission outlining the consequences that it says such a ban would have on farmers.
NFU vice-president Guy Smith says: "A blanket ban of neonicotinoids would not only impact major crops such as cereals but also sugar beet and vegetables, as there are no effective alternatives to neonicotinoid seed treatments which form an incredibly important part of integrated pest management. By denying UK farmers these key crop production tools, our competitors who have access to these products are being gifted a market."
The calls have coincided with the publication of further research that is critical of the pesticides. A recent study by Royal Holloway University of London on the neonicotinoid insecticide thiamethoxam found that it reduces ovary development in queens of four bumblebee species when present at "field-realistic levels".
Lead author Dr Gemma Baron says: "Previous studies have focused on a single bumblebee species and examined impacts in workers and established colonies. But bumblebee populations rely on spring queens to succeed and by looking at the impacts of thiamethoxam on multiple species of spring queens we have gained a step change in our understanding."
Co-author Professor Nigel Raine adds of the EU's proposals: "This work adds significantly to the evidence base on which to make such important policy decisions."
NFU horticultural policy adviser Dr Chris Hartfield says of the research, published in Proceedings of the Royal Society B: "This is another interesting piece to an unsolved puzzle about how neonicotinoids affect bees. But it does not show that under real-life field conditions, where bees forage naturally on treated crops, neonicotinoids are causing widespread declines in pollinator populations. Farmers are well aware of the importance of bees and would not want to cause population declines."
On the EU proposals, he adds: "There are still knowledge gaps and a limited evidence base to guide and inform policymakers on this issue."
Meanwhile, a report published this month by the US Center for Food Safety has found "continued widespread water contamination from neonicotinoid insecticides ... at levels known to be toxic to several aquatic invertebrates", which it says can lead to "rippling negative effects throughout the food web".
A University of Iowa study earlier this year found neonicotinoids in local drinking water. It concluded that the chemicals "are likely present in other drinking water systems across the US". The main use of neonicotinoids, as seed coatings, remains unregulated by the US Environmental Protection Agency.