Pesticides don’t just kill pests. New research from the Netherlands provides compelling evidence that a widespread class of insecticides has been linked to population declines in 14 species of birds.
These insecticides, called neonicotinoids, have been in the news lately because they harm bees and other pollinators. (Related to: “The plight of the honeybee.”)
This new paper, published online in Nature on Wednesday, explores a different angle of history – the ways these chemicals can indirectly affect other living things in the ecosystem.
Scientists from Radboud University in Nijmegen and the Netherlands Center for Field Ornithology and Bird Life (SOVON) compared long-term data sets for both farmland bird populations and chemical concentrations in surface water. They found that bird populations in areas where the water contained high levels of imidacloprid – a common neonicotinoid pesticide – tended to decline an average of 3.5 percent annually.
“I think we’re the first to show that this insecticide can have far-reaching, significant effects on our environment,” said Hans de Kroon, an expert on population dynamics at Radboud University and one of the study’s authors.
Second quiet spring?
Pesticides and Birds: If this story sounds familiar, it’s likely because Rachel Carson wrote about it back in 1962. Carson’s groundbreaking Silent Spring was the first popular attempt to warn the world that pesticides are contributing to “the sudden silence of birdsong.” “
“I think there is of course a parallel,” said Ruud Foppen, ornithologist at SOVON and co-author of the Nature Paper.
Foppen says that while Carson battled a completely different type of chemical – organophosphates like DDT – the effects he sees in the field are very similar. To be clear, neonicotinoids damage biodiversity.
“That way we can compare it to what happened decades ago,” he said. “And if you look at it that way, we haven’t learned our lessons.”
How neonicotinoids work
Over the past 20 years, neonicotinoids (pronounced nee-oh-NIK-uh-tin-oyds) have become the fastest growing class of pesticides. They are extremely popular with farmers because they are effective in killing pests and are easy to use.
Instead of loading gallons and gallons of insecticide into a grain vacuum and spraying it for hundreds of acres, farmers can buy seeds preloaded with neonicotinoid coatings. Scientists refer to neonicotinoids as “systemic” pesticides because they affect the whole plant rather than a single part. As the pre-treated seed grows, it incorporates the insecticide into each bud and branch, effectively turning the plant itself into a pest control machine.
This lock, stick and barrel method of plant protection means that the intruder, no matter where a grasshopper or a root worm likes to nibble – on the roots, on the stem, on the flower – gets a stomach full of neurotoxins.
“The crops become poisonous not only to the insects that farmers target, but also to beneficial insects like bees,” said Jennifer Sass, a senior scientist at the Natural Resources Defense Council (NRDC), who opposed the widespread use of neonicotinoids . Covering the pesticide from top to bottom means that the flowers, pollen, and nectar of the plants are also toxic.
Worse, Sass says, neonicotinoids can linger in the soil for years. This gives other growing plants a chance to come in contact with the chemicals and ingest them.
“So they actually end up in plants that grow on the edges of fields that should never be attacked,” she said.
Bye bye birdie
The new Nature paper shows strong evidence that neonicotinoids are dangerous even if not ingested.
The study examined population statistics of over a dozen bird species that are common on agricultural land in the Netherlands. Most of these species are wholly or partially dependent on insects for their food, but some also eat seeds and grains. This means that neonicotinoids can harm birds in the Netherlands in two ways.
The first is ingestion. Studies have shown that while neonicotinoids are considered safer for mammals and birds than for insects, they can be deadly in sufficiently high doses. And the best way to get a concentrated dose of neonicotinoids is to eat seeds coated with them. A 1992 study by the U.S. Environmental Protection Agency found that after consuming a tiny amount of imidacloprid, sparrows have difficulty flying and become immobile at higher doses.
The second way neonicotinoids can affect birds is to eliminate their food sources. Because these pesticides kill target and non-target species alike, there are fewer flies, grasshoppers, stink bugs and caterpillars for the birds to enjoy.
Causality vs. correlation
While the new paper shows a link between high levels of neonicotinoids and declining bird populations, it does not claim that the pesticides are a direct cause of the decline.
To make sure the correlation wasn’t accidental, the team analyzed a number of alternative explanations.
Caspar A. Hallmann is an ornithologist and population ecologist at SOVON and Radboud University. As lead author of the Nature paper, he explained that the causes of bird population decline are numerous, from changes in the types of plants grown in a given year and the amount of fertilizer used, to the urbanization of former farmland. But when the team looked at the data, none of these explanations held up.
Hallmann said that, as with any correlative study, caution should be exercised. “But still,” he says, “we believe we have a line of evidence that is building up.”
Pesticide manufacturers disagree
Bayer CropScience, the main manufacturer of imidacloprid, defends the use of neonicotinoids. In a statement to Hallmann and his colleagues, the company writes: “Neonicotinoids have undergone an extensive risk assessment which has shown that they are safe for the environment when used responsibly in accordance with the label instructions.”
The statement concludes by stating that the Nature paper does not establish a causal relationship and therefore “provides no substantiated evidence of the alleged indirect effects of imidacloprid on insectivorous birds”.
“We have indeed shown a negative connection that is very alarming,” said the Dutch scientists in response to Bayer CropScience’s criticism. “Proof of causal relationships at the ecosystem level would require experiments on a landscape scale,” which would be “difficult and probably very unethical”.
A third view
The Dutch scientists say that neonicotinoids negatively affect bird populations. According to Bayer CropScience, neonicotinoids are safe when used correctly. Who do we trust
Perhaps an independent group that has just completed a review of over 800 scientific studies on the effects of neonicotinoids on wildlife. The Task Force on Systemic Pesticides, made up of 29 multidisciplinary scientists, recently published its landmark report, Worldwide Integrated Assessment of the Impact of Systemic Pesticides on Biodiversity and Ecosystems.
Overall, the scientists came to the conclusion that even when neonicotinoids were used as intended and as intended, the concentrations of chemicals in the environment often exceeded the lowest levels known to be dangerous for a large number of species – and “therefore probably a wide range of negative biological ones and have environmental impact. “
Not just bees anymore
David Gibbons, member of the task force and head of the RSPB Center for Conservation Science, the largest conservation charity in Europe, stated that many European countries have already restricted three types of neonicotinoids – including imidacloprid – as there is increasing evidence that they harm the bees.
(So far, there are no similar safeguards in the U.S., even if it wasn’t due to a lack of testing – the NRDC only filed a petition this week asking the EPA to withdraw approval of neonicotinoid pesticides.)
“There have been a number of mass bee deaths in several European countries over the past decade,” Gibbons said.
When planting maize, the neonicotinoid coating can actually come off and the tractors throw the dust off the fields into the air.
“These dust clouds contain very high concentrations of neonicotinoids,” says Gibbons, “and are instantly fatal to bees.”
Part of the goal of the Worldwide Integrated Assessment Report, however, is to show that bees are not the only animals affected. The task force provides evidence that earthworms, aquatic invertebrates, lizards, fish and many other animals are attacked by systemic pesticides (direct or indirect).
Gibbons says it’s hard to tell whether we’ve entered a second “quiet spring”.
“However,” he adds, “[neonicotinoid] Its use is now so widespread – nearly 40 percent of the world’s insecticide market – that there is legitimate reason for concern. “