TWO ENZYMES, one found in honeybees and the other in bumblebees, may hold the keys to a new generation of insecticides that can protect crops without threatening pollinators.

Work led by Rothamsted Research, the University of Exeter and Bayer AG, has concluded that not all neonicotinoids are harmful to bees, and set about finding out why some of this chemical family get a clean bill of pollinator health – and if that property can be built upon.

“Some neonicotinoids are highly toxic to bees but others have very low acute toxicity; in public debate, they tend to get tarred with the same brush,” said Rothamsted's head of Biointeractions and Crop Protection, Lin Field, who led the project. “Each insecticide needs to be considered on its own risks and merits, not just its name.”

The research has been looking at bees' biochemical defence systems, and the specific enzymes that define their sensitivity to insecticides by enabling them to metabolise the chemicals safely. It's findings, published this week, extend previous work by other researchers, who had linked immunity to rapid metabolism, by pinpointing the specific genes, and their enzymes, involved. The discovery opens up the opportunity to design bee-friendly insecticides.

“Identifying these key enzymes provides valuable tools to screen new pesticides early in their development to see if bees can break them down,” said Exeter's Professor of Applied Entomology, Chris Bass. “It can take a decade and $260 million (£190M) to develop a single pesticide, so this knowledge can help us avoid wasting time and money on pesticides that will turn out to be harmful to bees. The knowledge from our study can also be used to predict and prevent harmful effects that result from inadvertently blocking these key defence systems.”

The EU introduced restrictions on the use of neonicotinoids in 2013 and, at the end of last month, the European Food Safety Authority published a review of research assessing the risks to bees that EFSA’s Pesticides Unit began in 2015, with the result that an extension to those restrictions is now being considered.

“Identifying the mechanisms that contribute to inherent tolerance helps us, and regulators, to better understand why certain insecticides have a high margin of safety in bees,” said insect toxicologist Ralf Nauen, who led the research group at Bayer.

The three main neonicotinoids are imidacloprid, thiamethoxam and thiacloprid – the first two contain derivatives of nitroguanidine, an organic compound, and can be as toxic to bees as they are to the pests they target. The third contain derivatives of cyanoamidine, another organic compound, which honeybees can digest. Bumblebees show similar responses.