Super insecticide imidacloprid has dramatic impact on insect richness in and around water

Insect numbers have been declining in recent years. Research by Utrecht University has found a link between the super insecticide imidacloprid and a decline in abundance of insects and other invertebrates in surface-water . Scientists are ringing international alarm bells. “Stricter standards alone are not enough. This insecticide is so harmful and remains in the environment for so long that an international ban is definitely warranted.”

Insecticide impacts on surface waters

In just over ten years, imidacloprid has become the most widely used insecticide in the world. Some 20,000 tons are produced annually and used on agricultural land and gardens to combat pests and insects that transmit plant diseases. However, the insecticide is used so widely, leaches so easily and is so poisonous and broad-acting that its lethal effect is not restricted to pests in fields and gardens. Research by Utrecht University’s Copernicus Institute of Sustainable Development has found the use of imidacloprid to have a highly adverse impact on insect abundance in and around surface waters.

Smartly combining monitoring data

Utrecht University scientists were the first to combine two long-term sets of monitoring data in a smart way to study the impact of imidacloprid on aquatic life in Dutch surface-water. As Jeroen van der Sluijs explains, “We see a strong link between situations in which imidacloprid levels in surface water exceed the standards and reduced abundance of aquatic insects such as dragonflies, mayflies, nonbiting midges, dipteran insects, and of snails and crustaceans. We were surprised to find, however, that there was one species that seemed to benefit from the poison: the higher the imidacloprid concentration, the more water mites there are.”

Fewer invertebrates

The pesticide was found to have adverse effects on surface-water ecosystems. The concentration of imidacloprid in the water was too high in almost half the sites monitored in the Netherlands in the past eight years. “On average we found three times less invertebrates in these locations than in water that meets the standard.”

25,000 times above the standard

In order to protect the environment, the government has established environmental quality standards that set risk limits for substances in surface water. The Utrecht study found these standards to have been grossly exceeded for many years. Some monitoring data showed the imidacloprid concentration in surface water to be 25,000 times above the standard. “That ditch water contained so much insecticide that it could actually be used directly as a lice-control pesticide. A bee or bumblebee drinking that water would die within a day.”Standards were found to have been exceeded in large parts of the Netherlands, based on the maximum permissable risk (MPR). However, even the MPR standard for imidacloprid (13 nanogram per litre) provides too little protection for insect larvae with a long aquatic stage, such as mayflies. The scientists found that even below the limit of 13 nanogram per litre, imidacloprid still adversely affected aquatic insect life. The substance has been used too widely and as a result the present standards have not been met for many years. As Van der Sluijs says, “Better enforcement or stricter standards alone are not enough. This insecticide is so toxic and remains in the environment for so long that its use needs to be cut back drastically. An international phase out is definitely warranted.”

International ban

The ecological impacts of imidacloprid have led to wide-ranging debates in many other European countries, as well as in the US and Japan, where a possible ban on neonicotiniode insecticides is being discussed. Europe decided earlier this week to restrict its use in crops attractive to bees. As Van der Sluijs explains, “We hope that the clear and convincing evidence that our study provides promotes the insight that this far too broad-acting poison is severely affecting our planet’s insect wealth. We are risking far too much to combat a few insect pests that might threaten agriculture. That is why this substance should be phased out internationally as soon as possible.”

The paper written by Tessa van Dijk, Marja van Staalduinen and Jeroen van der Sluijs on their research has been published in PLOS ONE. The research was financed by a grant from the Triodos Foundation, which has set up a special fund for independent research on this controversial group of insecticides.