Pesticides drifting to unintended flowers could harm pollinators, study finds

Being exposed to multiple pesticides is concerning for the health of bees and could have serious implications for crop production, the function of ecosystems and human health.


Bees need a balanced diet of nectar, which gives them carbohydrates in the form of sugars, and pollen, which provides fat and protein, from a wide variety of plant sources. Different bee species have their own nutritional needs, but no healthy bee diet includes pesticides.

According to new findings by scientists from Trinity College Dublin and Dublin City University (DCU), pesticides have been found in the nectar and pollen of flowers that were not targeted with the toxins, and this could be an extra, underestimated hazard for pollinators.

“This is the first time that a multi-field survey of pollen and nectar from crops and wild plants has been undertaken in Ireland and is critical to our understanding of pesticide residues in the Irish context,” said co-lead author of the study professor Jane Stout of Trinity’s School of Natural Sciences, according to a press release from Trinity College Dublin.

The study, “Pesticide mixtures detected in crop and non-target wild plant pollen and nectar,” was published in the journal Science of the Total Environment.

For the study, thousands of flowers were collected and analyzed by Trinity doctoral student Elena Zioga from agricultural fields throughout Ireland.

The researchers checked for the presence of residues from the herbicides fluroxypyr and glyphosate, as well as the fungicides azoxystrobin, boscalid and prothioconazole, in the pollen and nectar of crop and hedgerow plants that were not targeted with the chemicals.

The scientists also checked for the neonicotinoid insecticides acetamiprid, imidacloprid, clothianidin, thiacloprid and thiamethoxam, some of which — imidacloprid, clothianidin, thiacloprid and thiamethoxam — had not been applied recently and were not even approved in Ireland anymore. However, these toxins may persist in the environment for extended periods of time.

The research team detected and recorded several chemical compounds, most of which came from fields where there hadn’t been a recent application of the pesticides. The most common combination was residues from boscalid, azoxystrobin and clothianidin, with the latter seeming to remain for several years post-application.

“The research takes place in the context of Ireland reaching the ambitious European Commission target in the Farm to Fork Strategy of reducing the use and risk of chemical pesticides by 50%,” said co-lead author of the study professor Blánaid White of the School of Chemical Sciences at DCU, according to the press release.

In Ireland, insecticides, herbicides and fungicides are the most commonly used categories of pesticides. Crops that frequently attract pollinators, such as rapeseed, are likely to have been treated with pesticides from all these groups.

“Application of various pesticide compounds from different pesticide categories, at multiple time intervals throughout the cropping period, increases the risk of pollinator exposure to pesticide mixtures through pollen and nectar with unknown consequences in pollinator’s health,” said Zioga.

Some neonicotinoids that were banned by the European Commission in 2018 — which are known threats to pollinators — still linger in the environment.

“We found clothianidin residues in pollen and nectar of both plant species even though it hasn’t been applied for years. The fact that it remains present in pollinators’ food sources for so long is a concern,” Zioga said.

The pesticides detected by the scientists were more often mixtures of different types of pesticides rather than single compounds, which means understanding the effects these mixtures have on pollinators and other organisms not targeted by the toxins is crucial.

“Our findings can help us to understand which are the more hazardous pesticides in an Irish context, and also help us to understand what the risks associated with the different chemical pesticides are, so that we can more effectively reduce the risk associated with them,” White said in the press release.

Being exposed to multiple pesticides is concerning for the health of bees and could have serious implications for crop production, the function of ecosystems and human health.

“We don’t know the full impact on pollinators of consuming foods contaminated with multiple pesticides, and most of what is known is compound specific,” White said.

Zioga added that the effects on bee species other than honey bees needed to be studied as well.

“Moreover, the toxicity of single compounds is mainly being tested on honey bees, while we have scarce toxicity data on other wild bee species like bumble bees and solitary bees,” Zioga said.

Stout said the long-term effects of different compounds on pollinators also needed to be looked into.

“We need to understand how different compounds move through the environment, and the rate at which these compounds degrade, so that we can understand the extent of their persistence,” White said in the press release.


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