Apple trees pollinated by bumblebees exposed to neonicotinoid pesticides contained 36 per cent fewer seeds than those pollinated by unexposed bees.

The results are the first to show that neonicotinoids impair the insects’ ability to pollinate plants.

Previous studies have found that the controversial pesticides can affect bees and bumblebees, but haven’t measured whether it disrupts their ability to pollinate plants.

About 30 per cent of agricultural crops depend on pollination by insects or other animals, with an estimated global value to farmers of $360 billion a year.

“Our work highlights the importance of pollination services, and including that in the debate about whether to ban or restrict neonicotinoids is very important,” says Dara Stanley of Royal Holloway, University of London.

Pollen decline
Stanley and her colleagues exposed colonies of bumblebees to nectar that either contained a type of neonicotinoid known as thiamethoxam at levels typically found in nectar and pollen from treated crops and contaminated wild flowers. The bees exposed to neonicotinoids collected less pollen from apple trees and visited apple flowers less frequently than the other group.

This behaviour resulted in a reduction in the number of seeds found in the apples, an important indicator of the extent of pollination.

For several years, debate has raged about the size of the effect neonicotinoids have on bees. A temporary moratorium on their use on certain crops pollinated directly by bees – such as oilseed rape – is in place in Europe while the European Food Safety Authority undertakes a review of all the evidence.

In the US, a court ruling in September overturned the US Environmental Protection Agency’s earlier approval of a newer type of neonicotinoid.
“With apples, we consumers don’t care if it has fewer pips, but it’s very important for apple growers as there is evidence linking the number of seeds with apple quality,” says Stanley. And if neonicotinoids are disrupting pollination of apples, they are likely to also be disrupting pollination of many other crops, including strawberries, raspberries, oilseed rape, field beans and peas, as well as wild flowering plants.

Artificial conditions
“The obvious conclusion is that farmers using these chemicals could potentially experience reduced crop yields, as could their neighbours who may not be using the chemicals,” says Dave Goulson of the University of Sussex, UK. “There may also be knock-on effects for pollination of wild flowers growing on or near farms.”

Syngenta, a company that manufactures thiamethoxam, says the design for the experiment, with bee colonies only allowed to forage for an hour a day and apple trees placed in experimental tunnels, didn’t represent real-life conditions.

This means the results are not conclusive, says Peter Campbell of Syngenta. “They are premature and only representative of a single experiment conducted under artificial conditions both for the apple trees being pollinated and the method of exposing the bumblebees,” he says.

Another paper published this week by French researchers found that while neonicotinoid pesticides harm individual honeybees, whole colonies were able to recover in the wild.

Mickael Henry of the French National Institute for Agricultural Research in Avignon and his team found that honeybees foraging around treated crops die off at a faster rate than normal – but colonies were able to make up by boosting the number of worker bees in the hive.

Journal reference: Nature, DOI: 10.1038/nature16167; Royal Society journal Proceedings B; DOI: 10.1098/rspb.2015.2110