Neonicotinoids are neuro-active insecticides which derive their toxicity to target species from acting mainly agonistically on nicotinic acetylcholine receptors (nAChRs) on the post-synaptic membrane. This means that normal nerve impulses become impaired. Among neonicotinoids, imidacloprid shows a selective toxicity for insects or at least it should!
An interesting research, published by Tessa C. Van Dijk, Marja A. Van Staalduinen and Jeroen P. Van der Sluijs in the journal PLoS One, found that 70% less invertebrate species were found in water polluted with the insecticide imidacloprid compared to clean water. There were also far fewer individuals of each species in the polluted water so that this is the first study showing a clear effect in the field.
According to Van Dijk and colleagues:
Our regression analysis showed a significant negative relationship (P<0.001) between macro-invertebrate abundance and imidacloprid concentration for all species pooled. A significant negative relationship was also found for the orders Amphipoda, Basommatophora, Diptera, Ephemeroptera and Isopoda, and for several species separately. The order Odonata had a negative relationship very close to the significance threshold of 0.05 (P = 0.051). However, in accordance with previous research, a positive relationship was found for the order Actinedida.
… that means that this comound is killing mayflies, midges and molluscs and we can not exclude that the pollution could have a knock-on effect on birds such as swallows that rely on flying insects for food.
In an interview to The Guardian, Julian Little, spokesman for Bayer Cropscience, which manufactures imidacloprid, said that “There doesn’t appear to be anything hugely surprising in this article. It shows the presence of high levels of insecticide in water can have effects on aquatic insects and other invertebrates. Should we have strong stewardship of insecticides to minimise any contamination of water? Yes we should and yes we do.”
It is true that the problem is not the molecule itself, but its use or better its abuse, but we have to understand what is happening in the several reported cases of extreme pollution, with imidacloprid levels 25,000 times the limit where the water contained so much insecticide that it could actually be used directly as a lice-control pesticide!
Van Dijk, T., Van Staalduinen, M., & Van der Sluijs, J. (2013). Macro-invertebrate decline in surface water polluted with Imidacloprid PLoS ONE, 8 (5) DOI: 10.1371/journal.pone.0062374