Neonicotinoids – the group of pesticides now well-known for the risk they pose to bees – didn’t always have an image problem. First introduced in the 1990s, they were considered an environmentally friendly option due to the way they specifically target insects, making them safer for vertebrates, including humans. Unfortunately, this effectiveness makes them lethal, not just to the pests they are intended to tackle, but also to pollinating bees. As a result, in 2013, the European Union introduced a moratorium on the use of three neonicotinoids in bee-attractive crops. This was later followed by a total ban of the same three on all outdoor crops in 2018.

The problem is, these lethal pesticides haven’t gone away. The same properties that make them effective also ensure they are highly persistent. Not least, the fact that they are water-soluble (allowing them to move throughout the entirety of a plant) means they travel easily through the surrounding environment. Recent research on 291 oil seed rape fields in the west of France has revealed that between 2014 and 2018, the three neonicotinoids in question were all present in samples. One of the three, Imidacloprid, was detected each year in 43 per cent of the analysed samples (corresponding to 48 per cent of the fields), with no downward trend over the years.

As oil seed rape is a bee-attractive crop, these pesticides would not have been applied directly since 2013. The researchers therefore believe the neonicotinoids must have spread to the rape fields from other crops where their use was still allowed. ‘I believe that part of it stems from cereals planted a year before, or a couple of years before, sowed on a nearby field,’ says Dimitry Wintermantel, a researcher at the French National Centre for Scientific Research. ‘At the moment of sowing, the neonicotinoids can be blown away like dust clouds of a very high concentration. And then later they can transport through water.’

Having analysed the quantities of the pesticides, the researchers carried out an assessment of the resulting risk to bees, which revealed that for two out of five years, at least 12 per cent of the fields were sufficiently contaminated to kill 50 per cent of the bees and bumblebees foraging on them.

The ban imposed in 2018 should now prevent further contamination, but getting rid of the chemicals already present is more difficult. The researchers hope this will provide food for thought for any country considering reintroducing the pesticides and for the many countries outside the EU that still allow their use.

Get the best of Geographical delivered straight to your inbox by signing up to our weekly newsletter and get a free collection of eBooks!