Pollinator research continues to flourish

Update provided by Prof. Jane Stout, Trinity College Dublin


This blog is part of the ‘Dispatches from Researchers’ series, which features guest articles written by experts in pollination and related fields.


In 2022, we published a research update for World Bee Day, including highlights from the Irish Pollinator Research Network.  This year, I’m thrilled to announce that EIGHT pollinator PhDs have been completed by students who are part of the network in the last 12 months. They all completed their studies, despite severe Covid-19 restrictions during the key data collection and analysis phases of their PhDs. And so a massive congratulations to them all!

So here they all are and what they have been working on…  


Elena Zioga 

Title of PhD - Characterizing pesticide residues in floral resources for bees 

Supervisors - Jane Stout (Trinity College Dublin) and Blanaid White (Dublin City University) 

Key findings from PhD  

Pesticide residues were found in plant pollen, nectar, and bee pollen, not only in crops but also in nearby non-target wild plants 

Bees may be exposed to combinations of pesticides from different chemical groups, with potentially severe negative impacts on their health. 

Neonicotinoid insecticides were detected in plant pollen and nectar several years after their outdoor ban in Europe, highlighting the need for constant and long-term monitoring.  

Glyphosate, a herbicide, was detected for the first time in wild plant nectar and pollen when used as a desiccant on crops, emphasizing the need to re-evaluate its use and necessity 

More research is needed to understand how different compounds behave in different climates and landscapes, including herbicides and fungicides apart from insecticides.  

Links to published papers - 1st author: Plant protection product residues in plant pollen and nectar: A review of current knowledge/ Glyphosate used as desiccant contaminates plant pollen and nectar of non-target plant species/ Pesticide mixtures detected in crop and non-target wild plant pollen and nectar / Co-authored: Bumblebees can be Exposed to the Herbicide Glyphosate when Foraging / Improving pesticide-use data for the EU 

What I am doing now – I am discussing future projects and collaborations towards safeguarding pollinators from pesticide use. 


Irene Bottero  

Title of PhD - Impact of landscape characteristics on flower-visiting insects in agricultural environments across Europe 

Supervisor – Jane Stout (Trinity College Dublin) 

Key findings from PhD  

The characteristics of the landscape (configuration and composition) and the climate (temperature and precipitation) impact on the abundance of flower-visiting insects in cultivated crops across Europe (oilseed rape crops and apple orchards), even though this effect is taxon-dependent. 

Semi-natural habitats and non-cultivated features positively impact different groups of insects in the two target cultivated crops, at different spatial and temporal scales. Higher abundance of insects in agricultural crops were related to habitat diversity and to the presence of non-crop and less-intensively managed habitats, at a 1 km radius, across Europe. When comparing different locations in cultivated crops in Ireland, we found more hover flies and butterflies along the margins of the crops, compared with their centre, across different seasons, suggesting that flowering margins might provide alternative food resources to the main crop.  

There is an indirect role of the habitats at shaping insects communities. Higher percentages of pollen of non-crop origin were found in those nests of Osmia bicornis, located in sites surrounded by abundant non-crop areas and by diverse habitats. Because more adults hatched in those sites where a higher percentage of non-crop pollen was found, we assumed that non-crop habitats could indirectly support the fitness of O. bicornis, providing high quality pollen or lower insecticide risk. 

Some types of cultivation can positively impact on the abundance of some insect groups. More insects (with the exception of bumble bees) were recorded across Europe in those sites located in oilseed rape crops, rather than in apple orchards. Similarly, O. bicornis nests located in oilseed rape crops were associated with higher rates of occupation and with more adults hatching. However, some contradicting results emerged, showing that crop effect is taxon-specific.  

Our results suggest a positive response to maintaining non-crop habitats and semi-natural features for supporting insect abundance in different types of agricultural contexts. Such features can be constituted by floral strips and hedgerows of non-cultivated plants in the immediate vicinity of the cultivated field, or by meadows.  

Links to published papers- 1st author: Impact of landscape configuration and composition on pollinator communities across different European biogeographic regions / Taxon-specific temporal shifts in pollinating insects in mass-flowering crops and field margins in Ireland / Co-authored: Monitoring bee health in European agro-ecosystems using wing morphology and fat bodies/ Design and Planning of a Transdisciplinary Investigation into Farmland Pollinators/ Stem-nesting Hymenoptera in Irish farmland: empirical evaluation of artificial trap nests as tools for fundamental research and pollinator conservation  

What I am doing now – I am currently studying the impact of pesticides on a solitary bee species known as red mason bee (Osmia bicornis). In particular, I am investigating the impact that pesticides, found in the pollen stock in the red mason bee nests, can have on the pupae and the adults of this species. 


Merissa Cullen 

Title of PhD - Investigating the effects of non-insecticide pesticides widely used in Irish agriculture on the bumblebee Bombus terrestris 

Supervisors – Jim Carolan (Maynooth University) and Dara Stanley (UCD) 

Key findings from PhD  

The herbicide glyphosate does not alter bee survival, but can cause sub-lethal impacts on the brain, digestive tract, and fat body at the molecular level at a low concentration.  

The fungicide prothioconazole does not alter bee survival but leads to some sub-lethal alterations on the brain, digestive tract, and fat body at the lower level at a field-realistic concentration.  

Both glyphosate and prothioconazole alter the digestive tract microbiota, with the common formulation RoundUp Optima+® altering the fungal microbiota differentially to glyphosate alone.  

Commercial formulations used by agricultural workers and homeowners may have alter bumblebees at the molecular level differentially to the pesticide active ingredient alone, leading to differential impacts on cell structural integrity, metabolism, and neural functioning in the digestive tract, fat body, and brain, respectively.  

There is a lack of research on the impacts of herbicides and fungicides on bees, particularly on bumblebees and solitary bees. Further, we know very little about the impact of ingredients found in pesticide formulations on the market on bees.  

Published papers:  

Fungicides, herbicides and bees: A systematic review of existing research and methods 

What I am doing now – I have recently successfully passed my PhD Viva!


Alison O’Reilly 

Title of PhD – From pesticides to pollination: conserving beneficial insects in agroecosystems 

Supervisor – Dara Stanley (UCD) 

Key findings from PhD  

We found that abundance and type of pollinators found in Irish oilseed rape fields vary depending on the time of year that the crop flowers and that these pollinators might come into contact with pesticides used in these fields. 

When bumblebees were exposed to certain insecticides and then forage, they collected less pollen to bring back to their nest which is needed for the colony to grow and develop more bees. 

When solitary bees were exposed to certain insecticides, their behaviour when foraging changed and they are a bit more ‘excited’ than normal bees. When they were exposed to these insecticides several times, their delivery of pollination services was reduced, and fewer apples were produced after being pollinated by these bees. 

We found that exposure to pesticides didn’t affect the survival success of bumblebee queens that went into hibernation, however, if they were exposed again once they woke from hibernation, this reduced the lifespan of the queens, meaning they didn’t live long enough to produce a full colony. 

What I am doing now – I am a post-doctorate researcher, continuing to investigate how pesticides and other stressors affect bees.  I hope to continue in this field of research and answer questions that may help with bee conservation and moving towards more sustainable agricultural systems. 


Linzi Jay Thompson  

Title of PhD - Behavioural and reproductive responses of bumblebees to pesticides 

Supervisors – Dara Stanley (UCD) and Jane Stout (TCD) 

Key findings from PhD  

We found that non-insecticidal pesticides (fungicides and herbicides) are very understudied in relation to bee health, and as such we have little understanding of what these pesticides may do to bees. We found that the weedkiller glyphosate (i.e. the active ingredient in formulations such as Roundup) had mixed effects on bee health, but that it may have the potential to reduce their motivation to forage and maybe even disrupt their sensory systems. We found that the fungicide prothioconazole may reduce a bees ability to grow and reproduce at the colony level – which may have consequences over repeated generations. These results indicate that even though these pesticides are not designed to target insects, they may still have negative consequences for insects such as bees.  

Published papers:  

Contrasting effects of fungicide and herbicide active ingredients and their formulations on bumblebee learning and behaviour / Bumblebees can be Exposed to the Herbicide Glyphosate when Foraging  

What I am doing now – I’m working in insect farming, where we rear maggots on waste food, to feed to hens as a sustainable alternative to soy based animal feed.  



Cian White 

Title of PhD - Nature and People in Anthropogenic Landscapes: an ecological perspective. 

Supervisor – Jane Stout and Marcus Collier (TCD) 

Key findings from PhD  

Nature-based Solutions can be created when ecosystem services, the benefits that flow from nature, contribute most to solving the problem at hand.  

Agriculture and urbanisation strongly structure the types of plants that occur in a landscape, which in turn structures the foodwebs between plants and pollinators. 

Semi-natural habitats like hedgerows are very important refuges for pollinators in intense agricultural landscapes, providing shelter to 50% of the pollinator population on just 5% of the land area 

Conserving lots of small semi-natural habitats is better than conserving an equal area of a few large semi-natural habitats in agricultural regions, but not cities. 

Florally diverse wildflower meadows are more aesthetically pleasing, provide better pollination to plants and are home to a higher diversity of pollinator species, thus increasing floral diversity provides multiple benefits. 

People who are ecologically knowledgeable tend to prefer more florally diverse meadows, while people who are not familiar with wild plant species do not prefer meadows that are florally diverse, suggesting that ecologically knowledgeable form inner critics and become more discernible.  

Published papers:  

Using ecosystem services to measure the degree to which a solution is nature-based / Anthropogenic Induced Beta Diversity in Plant–Pollinator Networks: Dissimilarity, Turnover, and Predictive Power / Conserving diversity in Irish plant–pollinator networks  

What I am doing now – I’m working as a postdoctoral researcher on the ‘FarmZeroC’ – a project that is creating a carbon neutral and biodiversity rich dairy farming model, demonstrating that dairy farming can become sustainable for people, planet and profit. 


Sarah Larragy 

Title of PhD - Evaluating wild and commercial populations of Bombus terrestris ssp. audax (Harris, 1780): from genotype to phenotype  

Supervisor – James Carolan (MU) and Jane Stout (TCD) 

Key findings from PhD  

My thesis research found that Irish populations of B. t. audax, the buff tailed bumblebee, show genetic distinctions from British populations of the same. We also found that the immune genes of the Irish population of B. t. audax are undergoing different selective pressures i.e. evolution is acting to change some genes, while conserving others. Finally, my thesis found a behavioural and proteomic differences between colonies of lab-reared wild and commercial buff tailed bumblebees.  

Published papers:  

Signatures of Adaptation, Constraints, and Potential Redundancy in the Canonical Immune Genes of a Key Pollinator  

What I am doing now – I have just passed my viva and am working on getting some of my work from my PhD research published.  


Arrian Karbassioon 

Title of PhD – How weather and time influence pollinator activity: implications for pollination services and agricultural management 

Supervisor – Dara Stanley (UCD) 

Key findings from PhD  

While honeybees are most active in dry and warm weather, bumblebee and hoverfly flower visitation may compensate for a lack of honeybee activity in colder, windier, and wetter conditions 

Wild insects such as solitary bees and hoverflies carry the most pollen in warm and cold weather, respectively, and warrant further consideration as potentially important pollinators 

While honeybees, bumblebee, and hoverfly activity largely overlaps throughout the day, bumblebees and hoverflies are active earlier and later than honeybees; we should be conscious that wild pollinators may be present in fields during times it is recommended to apply pesticide (usually in the morning or evening) 

Published papers:  

Responses in honeybee and bumblebee activity to changes in weather conditions  

What I am doing now – I will be researching the effects of extreme heat on bumblebees visiting crops and wild plants, and how surrounding vegetation density influences field temperatures.