Photo Shutterstock Without intending to, bees collect all kinds of material when flying around. It is not just pollen that sticks to their bodies, helping fertilize plants, but also pesticides and other substances. That makes these insects potential biomonitors. A study using beekeepers in all the EU countries has shown that this actually works really well.
The principle that bees could be used as tell-tales had already been demonstrated nine years ago by the Wageningen bee researcher Sjef van der Steen. He got bees to enter their hive through narrow tubes lined with an adhesive. The bees were thereby ‘stripped’ of the cargo they were unknowingly carrying. Van der Steen got a PhD for his pioneering work.
Tenax
His method formed the basis for the European monitoring project, which WUR researchers Ivo Roessink and Bas Buddendorf worked on in addition to Van der Steen himself. This time, instead of the tubes, they used hard plastic strips with a layer of Tenax that binds volatile substances.
‘The strips were placed in the top of the beehive between the honeycombs,’ explains Roessink. ‘They were removed again after two weeks and analysed to see what substances were present. The bees were not bothered by this intervention at all. Normally they chuck everything out of the hive that they don’t recognize or trust, but they left this alone.’
The bee monitor is an example of citizen science: 315 beekeepers in the 27 EU countries took part in the experiment. The hives were sampled throughout the summer of 2023, and tests were carried out for over 400 different pesticides. A total of 188 pesticides were detected. None of the strips were without pesticide traces.
It is not really surprising the bees carried so much material. ‘If a bee flies onto a crop that has just been treated with a crop protection product, it’s only to be expected you’ll see that evidence,’ says Roessink. ‘To a large extent, the products we found match what is used in agriculture.’
But that was not always the case. The bee killer imidacloprid was found in one in three hives across Europe. With some exceptions, its use in field crops was banned ten years ago, although imidacloprid is still used in pet flea products.
Banned insecticides such as thiacloprid and chlorpyrifos were found in one in five hives. ‘Is that because people were being naughty,’ wonders Roessink, ‘or are those substances used in products that we didn’t know could get into the environment? Of course, we could also be seeing the residues of use in the past.’
DDT
A telling and worrying example of that last possibility is the fact that residues are still being found of the notorious product DDT, which has been banned for nearly 40 years. Despite, it was still found in one in four hives, albeit in very low concentrations. The detection threshold was down in fractions of a nanogram.
The bee monitor shows whether a pesticide is present, but not in what concentrations. This is inherent to the method. Roessink: ‘You only measure the amount of the substance on each strip. That substance comes from all the surrounding area and could have been brought in by a couple of bees or thousands. So you can’t deduce from this what the exposure is in the environment.’
The bee monitor provides qualitative information, which Roessink says can supplement the existing monitoring projects. He also sees possibilities in policy evaluation. ‘Imidacloprid is banned, so why are bees still returning with it on them? Is that policy actually working? This is a great method for determining that.’
