Neonicotinoids are one of the types of pesticides in the spotlight for their effects on beneficial insects in ecosystems and crops . Some of these, in particular imidacloprid, thiamethoxam and clothianidin have recently been banned by the European Commission for use in open agroecosystems due to their affection to honey bees .
The non-specificity of these pesticides makes them potentially harmful and their risks were reviewed by the EFSA (European Food Safety Agency). The analysis routes were three: residues in pollen and nectar, dust residues during sowing / application of the treated seeds; and water consumption.
However, in these cases , molasses , which is more abundant than nectar and can be another route of exposure to insecticides by beneficial insects, as well as pollinators in a wider range than the previous ones, had not been considered.
This new study published in the PNAS journal financed by the National Institute of Agrarian Research and the Conselleria d’Agricultura, Pesca i Alimentació de la Generalitat Valenciana, has shown that they can also affect plant molasses.
Melaza from mealybugs can carry traces of pesticides
The molasses is a sticky liquid produced by insects such as mealybugs , aphids, psyllids and whiteflies, which feed on plant tissues containing sugars. The insects leave the honeydew on the plants they visit, and other insects such as pollinating flyflies and parasitic wasps feed on them.
The main problem is that the insects that consume the contaminated honeydew and kill them are not the intended targets of the neonicotinoids , and include beneficial insects.
The researchers made this discovery by applying neonicotinoids to citrus trees, both directly as a spray and in irrigation water on the ground.
They then collected honeydew made from citrus mealybugs that fed on them and fed two types of beneficial insects: flies and parasitic wasps.
Most of the flies and almost half of the wasps died within three days of consuming the molasses. It is a data that is contrasted with the deaths in the control, within the same period of time only 6 to 15% of the flies and wasps died.
The researchers also took a closer look at the molasses samples and found detectable levels of neonicotinoids in a significant fraction of them . The molasses samples from the control trees did not show signs of neonicotinoids.
The results of the experiment show that beneficial insects may be killed by eating honeydew contaminated with neonicotinoids, suggesting a new source of danger to them, according to the researchers. For this reason, this route of exposure should be examined in the next risk analyzes carried out.