Pesticides decimating dragonflies and other aquatic insects

Jeremy Hance
June 18, 2013

While recent research (and media attention) has focused on the alleged negative impacts of pesticides on bees, the problem may be far broader according to a new study in the Proceedings of the US Academy of Sciences (PNAS). Looking at over 50 streams in Germany, France, and Australia, scientists in Europe and Australia found that pesticide contamination was capable of undercutting invertebrate biodiversity by nearly half.

"Pesticide use has not decreased in the last decade [...] and is predicted to increase in the next decades due to climate change and thus may be a more important driver of biodiversity loss in the future," the scientists write.

By comparing freshwater species in uncontaminated streams with those in highly-contaminated streams, the researchers found that invertebrate biodiversity dropped by 42 percent in polluted streams in Europe. Meanwhile in Australia, freshwater biodiversity fell by 27 percent between clean and contaminated streams.

Pesticide contamination hit some invertebrate groups the hardest including dragonflies, stoneflies, caddisflies, and mayflies. Such species did not necessarily disappear altogether, but saw their abundance plunged. While, many of the decimated species may not be well-known to the general public, they play a major role in the food chain, including as prey for birds and fish.

Notably, current regulations in Europe are not strong enough to protect these species, according to the scientists. They found that even in those contaminated sites that met EU regulations, biodiversity had plunged. This points to a rising controversy over proper testing and risk assessments for pesticides before they released into the public's hands.

"The current practice of risk assessment is like driving blind on the motorway," says co-author, Matthias Liess, an ecotoxicologist with the Helmholtz Centre for Environmental Research in Germany.

In April, the EU banned three pesticides for two years in a bid to stem bee losses on the continent. A flood of recent studies have shown an increasingly convincing connection between a type of pesticides, known as neonicotinoids, and colony collapse disorder (CCD) in bees. The pesticides likely don't kill the bees outright, but instead impair brain functioning leading to navigational and other problems, which is exacerbated by habitat and food loss as well as disease.

Insect species such as the Common Bluetail (Ischnura senegalensis) are particularly threatened by pesticide entries in their habitat. Photo by: André Künzelmann/UFZ (Place: Banaue/Phillippines).
Insect species such as the Common Bluetail (Ischnura senegalensis) are particularly threatened by pesticide entries in their habitat. Photo by: André Künzelmann/UFZ (Place: Banaue/Phillippines).

CITATION: Beketov, M., Kefford, B., Schäfer, R., & Liess, M. PNAS. Pesticides reduce regional biodiversity of stream invertebrates. 2013.

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Jeremy Hance
mongabay.com (June 18, 2013).

Pesticides decimating dragonflies and other aquatic insects.