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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Thursday 5th April 2012

The world of poisons, not exclusively poisonous plants, extends into a wide variety of areas of interest and, just occasionally, I see a link between two of them that may not be obvious or, to be fair, valid.

In the past week or so the issue of neonicotinoid pesticides has, again, been in the news with a number of new reports being published very close together. The main issue with these pesticides is whether they can harm bees and other pollinators. I’ve written before about bees and poisoning, first on the general topic of whether toxins can get into honey and later on the specific problem of Rhododendron poisoning of bees, so I was interested in these new reports.

Pulmonaria rubra 'Redstart'

A bee visits Pulmonaria rubra 'Redstart'

The term ‘neonicotinoid’ is not directly related to plants in the Nicotiana genus. When the receptors in the body that are affected by nicotine were identified they were named ‘nicotinic acetylcholine receptors’. The pesticides being discussed so widely act on the same receptors and, when first used in 1984, were called neonicotinoid. They are structurally similar to nicotine, in the same way that mephedrone is structurally similar to the cathinones found in Catha edulis, khat, but they are not obtained from the plant.

Extracts from Nicotiana plants have been used as insecticides, mostly home made by gardeners who would grow Nicotiana sylvestris, woodland tobacco, in order to soak the leaves in water for a couple of days and then use the water to spray onto other plants. These days such a use is illegal as all pesticides have to be approved for use by the UK government, even those described as ‘traditional’ home-made products. This abstract from 2004 shows what can go wrong with a nicotine pesticide.

The recent debate on the neonicotinoids has been sparked by three reports from three different countries. ‘Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production’ comes from researchers at two UK universities, French researchers published ‘A Common Pesticide Decreases Foraging Success and Survival in Honey Bees’ in the same edition of ‘Science’ and an American conservation group, The Xerces Society, published a report entitled ‘Are Neonicotinoids Killing Bees - A Review of Research into the Effects of Neonicotinoid Insecticides on Bees with Recommendations for Action’.

Aconitum napellus, monkshood with bees

Aconitum napellus, monkshood with bees

That last is the one that interested me most. For a long time, the pesticide industry and its supporters have argued that parasites are the cause of colony collapse disorder not the neonicotinoids. The Xerces Society report suggests that non-lethal doses of neonicotinoids weaken bees making them unable to resist the parasites. If true, that would explain why colony collapse disorder was not so common before the use of neonicotinoid pesticides.

I said ‘if true’ because none of these reports seems to be able to offer absolute proof that these pesticides are damaging to bee populations and at least two of the three call for further research. It is this continuing uncertainty that has led DEFRA to refuse an immediate ban on their use in the UK though some European countries have already imposed bans.

I started by saying that I sometimes see links between apparently entirely separate parts of the story of poison and poisonous plants and, later, I mentioned the situation with mephedrone. So, here’s my question – Why did the government think it was justified in banning mephedrone before the ACMD had completed its review of the evidence for harm but doesn’t feel justified in banning neonicotinoids, or even suspending their use, because, it says, the evidence isn’t strong enough to justify such action? 

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