Birds May Be Suffering Indirectly From The Use Of Neonicotinoid Insecticides

Declines in insect-eating bird populations on farmlands in the Netherlands that have coincided with the increased use of neonicotinoid insecticides suggest that the chemicals may pose a greater risk to the environment than previously believed.

Neonicotinoids are insect neurotoxins designed to wipe out pests that damage crops. The insecticides, manufactured by Bayer CropScience and Syngenta Crop Protection, are usually applied as seed dressings and are absorbed by seedlings and spread throughout the plants as they grow, protecting them from herbivorous insects.

Neonicotinoids have been linked to the decline of beneficial nontarget pollinating species such as honeybees. The chemicals are thought to be nontoxic to mammals and birds. However, Caspar A. Hallmann and colleagues of Radboud University, in the Netherlands, argue that neonicotinoids might be indirectly responsible for the observed decline in bird populations (Nature 2014, DOI: 10.1038/nature13531).

Bayer CropScience spokesman Utz Klages tells C&EN that the company’s scientists believe the study is inconclusive about the indirect effects of neonicotinoids, as the researchers “make no proper attempt to account for other possible sources of the reported declines, such as climate change.”

Hallmann’s team examined Dutch bird-monitoring data and surface-water quality measurements and found that 15 insect-eating bird species have been declining by 3.5% on average annually. The declines began in the 1990s and coincide with the introduction of imidacloprid, the most common neonicotinoid. The bird declines are most noticeable in areas where surface-water concentrations of the insecticide are above 20 ppt.

In December, the European Commission instituted a two-year ban on using neonicotinoids on flowering crops because of the concern over their effects on honeybees and other pollinators. Bayer CropScience and Syngenta Crop Protection have challenged the ban on the grounds that there is insufficient evidence to prove their useful products are to blame.

Yet the new study confirms what has been observed for years in Europe, says Jean-Marc Bonmatin of France’s National Center for Scientific Research, who has studied the environmental impact of neonicotinoids. Bonmatin notes that the study results are echoed in a soon-to-be-published global biodiversity assessment report by the independent scientific Task Force on Systemic Pesticides.

“The most important fact is that the researchers demonstrate a clear correlation of a cascading effect with imidacloprid contamination—it is beyond the direct effects that are already known on pollinators and soil invertebrates,” Bonmatin says. “This is a serious threat for the biodiversity of birds and probably of numerous insect-dependent species.”

Klages notes that Bayer is working with Dutch authorities and the agricultural community “to ensure the safe use of imidacloprid-containing crop protection products and to preserve the environment.”