500 dead bumblebees – pesticides leave their deadly trace

Earlier this year, Sheila Horne was walking at Hacton Parkway, a public park and conservation area in Havering, East London. April is normally a good time to see insects in their prime so she was very surprised to find many dead and dying bees near the path. She alerted local naturalist, Tony Gunton who identified the insects as bumblebee queens from three species, red-tailed, buff-tailed and common carder. This was not a minor incident, there were as many as 500 bees affected.

Natural England was appointed to investigate the insect deaths and samples of dead bees were sent to FERA in York for analysis. The results were released a few weeks ago and showed that the bees were contaminated with the neonicotinoid insecticide imidacloprid and two fungicides, flusilazole and epoxiconazole. Imidacloprid is very poisonous to bees with bumblebees being more susceptible to this chemical than honeybees. Imidacloprid is now subject to a two year partial ban for some agricultural uses. Neither fungicide on its own is especially toxic to bees although flusilazole is due to be phased out this October because of its high toxicity to fish and because of other potential toxic effects.

But where did the bumblebees pick up these chemicals? We cannot be sure but as so many dying bees were found together in one place, it seems likely that the source of the poisoning was close by. Hacton Parkway lies alongside arable farmland and at the time of the poisoning some of the land was planted with flowering oil seed rape, so it is a reasonable conclusion that the bees had been feeding there. It is thought that the crop had been sown in autumn 2013 using seed treated with imidacloprid, just ahead of the ban. According to John Rennie of Natural England there had been no spray applications of insecticides or fungicides since the beginning of 2014.

So, why did these bees die? Because there are so many unanswered questions we cannot be sure. The imidacloprid used on the oil seed rape has been blamed by some but I can’t see how this could be a problem if the farmer followed safety guidelines. There is good evidence that exposure to typical agricultural levels of imidacloprid does not kill bumblebees although there is also good evidence for sub-lethal effects on behaviour and reproduction. It is, however, becoming apparent that neonicotinoids such as imidacloprid accumulate in soil so perhaps exposure levels of the dead bees were higher than expected. Soil testing would be informative here.

There is also the question of how the bees were exposed to the two fungicides if no spraying was performed during the flowering season? Does this mean that these chemicals persist for long periods or has there been spraying elsewhere? Perhaps the fungicides weakened the bees or made them more susceptible to the imidacloprid. There is some evidence for such interactions for other insecticide/fungicide pairings.

Although the investigation continues, it may be quite difficult to resolve some of these questions. Despite this uncertainty, the results of the chemical analysis stand. These bees died with three chemicals in their bodies: one insecticide and two fungicides. This was no laboratory experiment; this reflects what is happening around us when these chemicals are used. Our agricultural practices have led to this and the result is the deaths of important pollinators. How often is this occurring on a lower level but not being noticed or reported?

With thanks to Tony Gunton for talking to me about this incident

9 thoughts on “500 dead bumblebees – pesticides leave their deadly trace”

  1. You summed it up, it has happened – how, we do not know but it can be assumed it is not an isolated incident. Such a large number of bees and queens at this time of year is shocking. At least it has been notified and hopefully it has been noted. There are too many unknowns about these insecticides and fungicides and the last people who want to know more are the producers. Amelia

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  2. Thanks for your comment, Amelia. I agree with all you say but I believe that there is more to be learnt about this incident if it is investigated properly and fully. Currently neither Natural England nor FERA will give me any more details because the “investigation is ongoing”. I hope they will investigate it fully and publish their findings. Philip

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  3. Nobody feels responsible… but insectes & birds are just being wiped away. Buterflies are nearly gone.

    If it is not the chemicals, what can wipe them at such scale.

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  4. Loss of habitat is also a very serious issue, I believe some of the effects of chemicals could be mitigated by replacement of habitat; this would cost farmers money but it might be a worthwhile price to pay.

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  5. Tragic. And without the observant eyes of Sheila and Tony sending samples for testing it would have gone unrecorded. Like you say, it seems likely these incidents are happening around the country.

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    1. Thanks Emily. What concerns me is that there is something significant to be learnt from what happened and the authorities are not really looking at this. For example I wonder if this is an example of chemical overload or chemical synergism leading to the deaths. If this were true it would be important information for farmers.

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