London Independent: None flew over the cuckoo’s nest: A world without birds.

It is nearly 50 years since Rachel Carson wrote Silent Spring, the book that warned of environmental damage the pesticide DDT was causing. Today, DDT use is banned except in exceptional circumstances, yet we still don’t seem to have taken on board Carson’s fundamental message.

According to Henk Tennekes, a researcher at the Experimental Toxicology Services in Zutphen, the Netherlands, the threat of DDT has been superseded by a relatively new class of insecticide, known as the neonicotinoids. In his book The Systemic Insecticides: A Disaster in the Making, published this month, Tennekes draws all the evidence together, to make the case that neonicotinoids are causing a catastrophe in the insect world, which is having a knock-on effect for many of our birds.

Already, in many areas, the skies are much quieter than they used to be. All over Europe, many species of bird have suffered a population crash. Spotting a house sparrow, common swift or a flock of starlings used to be unremarkable, but today they are a more of an unusual sight. Since 1977, Britain’s house-sparrow population has shrunk by 68 per cent.

The common swift has suffered a 41 per cent fall in numbers since 1994, and the starling 26 per cent. The story is similar for woodland birds (such as the spotted flycatcher, willow tit and wood warbler), and farmland birds (including the northern lapwing, snipe, curlew, redshank and song thrush).

Ornithologists have been trying desperately to work out what is behind these rapid declines. Urban development, hermetically sealed houses and barns, designer gardens and changing farming practices have all been blamed, but exactly why these birds have fallen from the skies is still largely unexplained.

However, Tennekes thinks there may be a simple reason. “The evidence shows that the bird species suffering massive decline since the 1990s rely on insects for their diet,” he says. He believes that the insect world is no longer thriving, and that birds that feed on insects are short on food.

So what has happened to all the insects? In the Nineties, a new class of insecticide – the neonicotinoids – was introduced. Beekeepers were the first people to notice a problem, as their bees began to desert their hives and die, a phenomenon known as Colony Collapse Disorder (CCD).

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If that is so, then neonicotinoid insecticides could be the root cause of the problem. But why are they so much worse than other insecticides?

“Neonicotinoids are revolutionary because they are put inside seeds and permeate the whole plant because they are water-soluble (which is why they are called systemic insecticides). Any insect that feeds on the crop dies,” explains Tennekes.

Even small doses can kill. Recent research, carried out on honey bees in the lab, showed that these insecticides build up in the central nervous system of the insect, so that very small doses over a long time period can have a fatal effect. The reason that neonicotinoids can have such a powerful long-term effect is down to the way they work – binding irreversibly to receptors in the central nervous systems of insects.

“An insect has a limited amount of such receptors. The damage is cumulative: with every exposure, more receptors are blocked, until the damage is so big that the insect cannot function any more and dies,” explains van der Sluijs.

And unfortunately the robust nature of neonicotinoids means that they can travel far beyond the crops they were used to treat. “Neonicotinoids are water-soluble and mobile in soil. They can be washed out of soils and into surface and groundwater – as we’ve seen in the Netherlands since 2004. As a result, neonicotinoids are probably readily taken up by wild plants as well, and in this way spread throughout nature, causing irreversible damage to non-target insects,” says Tennekes.

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