Insecticide Blamed for Bee Decline also Lethal to Aquatic Organisms

A new study shows neonicotinoid insecticides are lethal to freshwater invertebrates following low but constant exposure. This group of insecticides are in the headlines again following a partial EU–wide ban agreed in April 2013, as evidence of their toxicity to bees became indisputable. Thirty studies have now linked neonicotinoid insecticides to the global demise of bees and is a likely cause of the Colony Collapse Disorder as ISIS was among the first to suggest.

New evidence has now emerged of their toxicity to another species, the arthropod Gammarus pulex, a freshwater shrimp; a predictable effect of a highly water- soluble chemical present in surface waters.

The study, conducted by Dr Roman Ashauer and colleagues from Eawag (the Swiss Federal Institute of Aquatic Science and Technology, Switzerland) looked at how different exposures of Imidacloprid, made by Bayer, would impact feeding activity, lipid content, immobility and survival of the fresh water shrimp. They looked at both pulsed exposure – two high concentration pulses of 90 µg/L with either short or long intervals between pulses – aimed at mimicking natural fluctuations of water contamination, as well as constant low level exposures of the same overall amount as used in the pulse experiments, at 15 µg/L. The shrimp, collected from a stream in Switzerland, were exposed for either 14 or 21 days, revealing effects not seen in routine toxicology tests that do not include long-term exposure.

The results showed significant mortality with constant low-level exposure: 92 and 95 % of insects died in the 14 and 21 day experiments respectively, the remaining 8 and 5 % of living animals were immobilised by the insecticide. There was a reduction in the proportion of mobile animals over the entire course of the experiment compared with controls.

Feeding behaviour, as measured by the mass of leaf material eaten was significantly affected, consistent with reduced lipid content in the animals. The untreated animals had a lipid content of 1.4 % compared to exposed animals at 0.7 %, consistent with a significant reduction in feeding. Significant effects are more pronounced after 14 day experiment due to possible variability in background mortality, lipid reserves or fitness levels at different times of the year, the 14 and 21 day experiments being conducted in November and February respectively.

The decreased feeding rate implies that starvation is at least partially responsible for imidacloprid lethality.

High-level exposure immobilised the animals, but they recovered fast upon transfer to clean water after the pulses, and therefore no significant effect on feeding or lipid content was observed.

Read the rest of this report on the Institute of Science In Society website.

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