New findings on neonicotinoids have important implications as many food crops and wildflowers rely on bee pollination to reproduce

The world’s most widely used insecticides harm the ability of bumblebees to pollinate apple trees, scientists have discovered. The finding has important implications for agriculture and the natural world, say the researchers, as many food crops and wildflowers rely on bee pollination to reproduce.

There is good evidence that neonicotinoids harm bees but the new research, published in the journal Nature, is the first to show a negative impact on the vital pollination services bees provide.

In 2013 the EU suspended the use of three types of the pesticide for three years. But has since approved two new types, while the UK has partly lifted the suspension after lobbying from farmers.

“Bumblebees are major pollinators of apples and many crops around the world,” said Prof Nigel Raine, at the University of Guelph, Canada, and one of the research team. “The findings of this study have important implications for both society and the economy, as insect pollination services to crops are worth at least $361bn worldwide every year, and are vital to the functioning of natural ecosystems.”

The research, carried out at the University of Reading’s farm in Berkshire, exposed bumblebee colonies to different levels of neonicotinoid found in normal fields and then tested their ability to pollinate apple trees. Compared to unexposed colonies, the exposed bumblebees visited fewer trees and collected less pollen, resulting in apples with one-third less pips. The number of pips is an important sign of pollination success because it is associated with higher quality fruit, which are more valuable to farmers.

The exposed bees actually spent longer foraging, but were less effective, said Raine. “It is bizarre that they are not looking for food, which is what they should be doing,” he said. The study did not examine why the pesticide affected the bees’ behaviour, but other research shows neonicotinoids affect bees’ memory and ability to learn, which is vital in productive foraging.

Syngenta, the company that makes and sells the chemical (thiamethoxam) tested in the study, expressed doubt about the research. “The conclusion is premature and only representative of a single experiment conducted under artificial conditions,” said Peter Campbell, senior environmental risk assessor at Syngenta. In the study, all other pollinators were excluded. Also, the final number of apples was unaffected by whether the bees had been exposed to the pesticide or not. Raine said the apple quality was most important to growers, who often thin out orchards.

Prof Felix Wäckers, at Lancaster University and not involved in the research, said the impact on pollination in the study might actually be an underestimate, as wild bumblebees are likely to be exposed to neonicotinoids for longer than the two weeks tested. “It shows that farmers themselves bear an economic cost when using this group of crop protection products,” he said.

A separate study, also published on Wednesday, found that worker honeybees foraging in fields are more likely to die when exposed to Syngenta’s neonicotinoid. However, the field trial also found that the colony appeared to compensate for this by producing more workers and delaying the production of drones, the male bees that mate with new queens.

The results, published in the journal Proceedings of the Royal Society B, may explain why laboratory experiments showing harm to bees have not been replicated in the small number of field trials carried out to date.

The researchers, led by Mickaël Henry, at INRA in France, said: “It is urgent that risk assessors take into account the scientific evidence for behavioural disorders triggered by trace levels of neonicotinoids.” They said the changed behaviour might affect mating success. Cambell, from Syngenta, said the lack of effect at colony level was reassuring.

In 2013, Syngenta published research from a four-year field trial in the journal in PLOS ONE which concluded that thiamethoxam was safe for honeybees.

However, a new analysis, published in Environmental Sciences Europe, criticises the research. “We conclude the study has substantial scientific deficiencies,” wrote the authors. “These include limited exposure periods, the use of pure thiamethoxam instead of a commercial preparation, the failure to quantify colony losses in winter and the fact that 70% of colonies did not survive to the end of the experiment, as well as the lack of any statistical evaluation.”