Neonicotinoids also poison beneficials via honeydew

08-08-2019    02:00   |    Tessa Louwerens/Resource

Neonicotinoids can also be harmful to beneficial insects through honeydew. It was already known that this group of insecticides could reach bees via nectar and pollen, but this happens only when the crops are blossoming. Honeydew, however, is available all year round.

Neonicotinoids are the most widely used group of insecticides worldwide. They are used to combat harmful insects that eat plants, for example. ‘Recent studies have shown that insect populations are declining rapidly’, says Marcel Dicke, professor of Entomology. ‘An important question is how much of a role the insecticides play in this. The debate regarding side effects on beneficial insects mainly concerns bees, but it also affects many other species of beneficial insects. The effects of these insecticides are probably much further reaching than thought previously.’


The researchers discovered that beneficial insects are also exposed to neonicotinoids via honeydew, which is a sweet fluid produced by aphids, mealybugs and whiteflies, amongst others, and is an important food source for many insects. The study was conducted by researchers of WUR, the Instituto Valenciano de Investigaciones Agrarias and the Universitat de València and is published today in the prestigious journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).


The researchers treated orange trees with two different commonly used neonicotinoids. They then introduced mealybugs, which produce honeydew, on the leaves. ‘If the plant has been treated with neonicotinoids, the mealybugs will ingest it through the saps, and the neonicotinoids will then also end up in the honeydew’, Dicke explains. Chemical analyses showed that the Neonicotinoids were indeed present in the honeydew, and the researchers observed that parasitic wasps and hoverflies perished after they had ingested the honeydew.

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Photo credit: Staticd via Wikimedia Commons, Creative Commons Attribution-Share Alike 3.0 Unported license.

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