December 3, 2023


Exposure to pesticides also to insects in nature reserves

Even in nature reserves, insects are not protected from pesticides, as a study from 21 German protected areas revealed. The researchers found insecticides in all insect samples; On average, the animals carried 16 different pesticides. The insects had picked up these chemicals from the surrounding fields. In order to prevent this in the future, according to scientists, nature reserves should be surrounded by buffer zones with only ecological agriculture.

Over the past few decades, the number of insects has decreased sharply around the world. In Germany alone, the biomass of flying insects has decreased by 75% in 27 years, and other arthropods are also measurably lower, long-term studies have shown. In addition to habitat loss due to extensive land use, pesticides are also suspected as possible causes.

A research team led by Karsten Bruhl of the University of Koblenz-Landau investigated the extent to which such pesticides were introduced into nature reserves and the insect contamination there. To do this, they evaluated insect samples caught in so-called Malay traps for a year. Animals fly into a kind of net cage and fall into a container with alcohol. This not only preserves them, but also acts as a solvent for pesticides. This enabled scientists to analyze pollution directly in and on insects. “With our method, 92 pesticides currently approved in Germany can be analyzed in small quantities simultaneously,” explains Brull’s colleague Nikita Bakanov.

No sample without pesticides

The result: none of the 21 nature reserves examined were free of pesticides. Instead, the researchers found an average of 16.7 different chemicals in the animals — the range ranged from seven to 27 jointly detected insecticides. “Our data clearly shows that insects in nature reserves are contaminated with a mixture of pesticides,” Brull says. This can increase the harmful effect through interactions of factors with each other and biological effects that reinforce each other. Scientists have long suspected that this cumulative effect of pesticides could be critical to the insects’ decline.

Of the 47 pesticides detected, 13 were herbicides, 28 fungicides used against fungal attack, and six were insecticides. Scientists have even discovered the neonicotinoid thiacloprid, which has been banned outdoors since August 2020, in insects from 16 out of 21 nature reserves. “The frequent occurrence of tricloprid in our samples may reflect that farmers took the last opportunity to inject their stock of this agent,” Brull and colleagues explain. In order to enable farmers to do exactly that, they were given a transition period until February 2021 to “taper” from the agent. But this is precisely what led to the use of an especially large amount of harmful thiacloprid. “It therefore seems advisable not to allow such transition periods and to destroy stocks rather than releasing them despite the proven adverse effect,” the researchers say.

Buffer zones are necessary

But where do pesticides come from in the midst of nature reserves? In Germany, the use of nebulizers within these protected areas is prohibited. So the research team combined its data with an ecological spatial analysis. “We wanted to find out where the insects ingest the pesticides,” explains co-author Lisa Eichler of the Leibniz Institute for Eco-Spatial Development in Dresden. This showed that the source of the pollution is not the protected areas themselves, but the surrounding fields. The researchers explained that “the flight paths of insects vary from less than a hundred meters to several kilometers.” According to their data, the flight radius of the examined insects was on average two kilometers – and thus extended far into the traditionally cultivated landscapes.

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According to Brull and colleagues, this shows that improvements in nature reserve areas urgently need action. Since most nature reserves in Germany hitherto were fairly small and did not have a buffer zone for spray fields – these fields often directly abut protected areas. Based on their results, the scientists call for the establishment of buffer zones two kilometers wide around the protected areas in order to better protect the insects. “Habitats that are strictly protected under EU law will in fact also be protected from the effects of pesticides,” Brull says.

Source: Koblenz-Landau University. Technical Article: Scientific Reports, doi: 10.1038/s41598-021-03366-w