How to Be concerned

Does anything eat a wasp? Despite the popularity of the question, which spawned a series of bestselling books, the answer is less interesting than one might think. Yes, many things eat wasps - big wasps, for starters. Then there's the bee-eater (don't blame it, we chose the name) and hundreds of other bird species. Perhaps instead one might ask, is there anything a wasp doesn't eat?

Many of these birds also eat bees and other insects. So it's worth asking a different question: If the numbers of these insects dwindle, will the birds that feed on them have enough to eat?

This suggestion is based on the observed correlation between the decline in populations of some agricultural land birds and the use of neonicotinoid insecticides in the Netherlands. The analysis indicates that pesticide use may have reduced the amount of prey insects available to birds, leading to the observed association, and suggests that neonicotinoids pose an even greater risk to wildlife than previously thought. We do.

Correlation, as every science blogger reporting this story will point out, is not the same as causation.

The evidence that agricultural chemicals may be to blame for the bird's loss is circumstantial, based on the finding that the sharpest decline occurred in areas of the country that also showed the highest water concentrations of imidacloprid, the most commonly used Known neonicotinoid. But the authors also rule out confounding effects from other land-use changes or pre-existing trends in bird declines.

Insects form a large part of the diet of many bird species during the breeding season and are important for producing offspring. Of the 15 species examined, nine eat insects exclusively, and all feed insects to their young, which supports the theory that pesticide use can negatively affect bird populations by reducing their food sources.

Used to be. Still, although many birds eat bees, none of the ones studied will generally eat them in any quantity. So a new question needs to be addressed: If pesticides are killing birds, how are they doing it?

In an accompanying News & Views article, ecologist Dave Goulson suggests one possibility (D. Goulson Naturehttp://dx.doi.org/10.1038/nature13642;2014). Almost all neonicotinoids used end up in soil and water as a pollutant. Some can be taken up by non-crop plants, such as hedgerows. Surrounded by contaminated food and water, aquatic insects and grasshoppers, beetles and caterpillars can be poisoned – as are bees – and therefore may not be around to feed the birds.

The picture is incomplete, and thus Goulson's call to Rachel Carson's Silent Spring, a tale of ecological destruction, may seem premature. But his voice is not alone.

An international assessment on the potential impact of neonicotinoids issued by scientists (including Goulson) late last month warned that the consequences for biodiversity and the human food supply could be dire (see go.nature.com/gzhg94). And Europe has already imposed a two-year moratorium on the use of three common neonicotinoids on flower crops.

So what eats a wasp? Yes, and we have to do more to ensure that.