Pesticides detected in Irish pollen and nectar may pose long-term hazard for bees

Neonicotinoid insecticides found in wild flowers despite being banned in 2018

Commonly-used pesticides used in agriculture production have been detected in wild Irish flowers in what could be “an additional, underestimated threat to pollinators”, according a study by scientists at Trinity College and Dublin City University.

The researchers looked for pesticide residues in the nectar and pollen of both crop and nearby “non-target hedgerow plants”.

“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 Prof Jane Stout, of TCD, who led the research with Prof Blánaid White in DCU.

It takes place in the context of Ireland trying to reaching the ambitious European Commission target in the farm to fork strategy of reducing use and risk of chemical pesticides by 50 per cent, Prof White said.


“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,” she added.

Pesticides are widely used to maximise food production by preventing crop damage and disease. The most widely applied pesticide categories in Ireland are herbicides, fungicides and insecticides. Crops attractive to pollinators – like oilseed rape – are likely to receive a pesticide input from all these categories.

“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 PhD researcher Elena Zioga.

Levels of the fungicides azoxystrobin, boscalid and prothioconazole and herbicides fluroxypyr and glyphosate, which are among the most applied pesticides, were evaluated in the study published in Science of the Total Environment.

The researchers also looked for the neonicotinoid insecticides, some of which have not been recently applied, as their approval has expired but may stay in the environment for long periods.

They found several compounds, the majority of which originated from fields where there was no recent application of these insecticides. The combination of azoxystrobin, boscalid and clothianidin residues in pollen and nectar of both oilseed rape and non-target bramble flowers, was the most common – with clothianidin appearing to linger for several years after its application on sampled sites.

Ms Zioga collected thousands of flowers from agricultural fields across Ireland, and carried out chemical analysis at DCU Water Institute.

Finding neonicotinoids, known to threaten pollinators, still lingering despite a 2018 ban by the European Commission “is a worry”, she added.

There was a need to know the extent of their presence in the environment, and at what concentrations, she said. “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.”

“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,” Prof White noted.

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

Bees and other pollinators can benefit from food sources provided by certain crops, however exposure to multiple pesticides applied on crops is of concern for bee health and for the sustainable delivery of pollination services, which consequently may have significant implications for ecosystem function, crop production, and human health.

“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,” Prof White said.

The study was part of PROTECTS (protecting terrestrial ecosystems through sustainable pesticide use) project, which was funded by the Department of Agriculture and Food.

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times