The effects of understudied agrochemicals and parasites on bumble bee (Bombus terrestris) health: How co-formulants, glyphosate and Crithidia bombi affect a wild pollinator species.

In the wild, bees face a number of distinct threats to their continued existence. This is of concern because bees play an essential role as pollinators in both agriculture specifically, and more broadly in non-agricultural ecosystems. To humans, bees are particularly important for pollinating nutritionally rich foods like fruits. The threats facing bees are multifactorial with habitat destruction/fragmentation, agricultural intensification, monoculture, climate change and pesticides all cited as drivers of their declines.

The work presented in this thesis focusses on elucidating the role of pesticides in bee declines by using laboratory testing to measure the effects of pesticide exposure on the buff-tailed bumble bee, Bombus terrestris. The usage and history of pesticides is detailed in the introductory chapter, as well as the effects of parasites on bee health. I have focussed on lesser studied agrochemicals like herbicides, fungicides, adjuvants and co-formulants because their effects on bees are poorly understood.

Chapters 2 and 4 present novel experimental research finding severe mortality effects of co- formulants present in herbicides and a fungicide respectively. In both instances the mortality and sublethal effects observed were not detected by regulators, highlighting that regulatory testing poorly characterises the impacts of co-formulants on bees. These experiments both challenge the notion that co-formulants are toxicologically ‘inert’. Stemming from these results, several recommendations for policy makers are made on how to regulate co- formulants better.

In Chapter 5 of my thesis, I present a systematic review summarising the current state of knowledge on the effects of co-formulants or adjuvants on bees. The review finds several key knowledge gaps, particularly highlighting a lack of understanding of what real world exposure to co-formulants and adjuvants looks like.
Much like the field of co-formulant and adjuvant research, how multiple concurrent stressors affect bees’ health is often overlooked, despite considerable exposure to multiple stressors in the wild. To address this, I undertook a series of experiments exposing bumble bees to two very common stressors, the world’s most used pesticide active ingredient, glyphosate, and a highly prevalent trypanosome parasite, Crithidia bombi. No effects of glyphosate on any metric recorded were found, and, contrary to prior research, no effect of C. bombi either. Further, no interaction between stressors was found.

The overarching results are synthesised in the concluding chapter, alongside a series of recommendations on how to better protect and study pollinators. Overall, the most compelling result was that co-formulants and adjuvants are a potential threat to bees. However, the research presented here alone is insufficient to conclusively determine if they are damaging as used in the field. Instead, this research presents progress towards determining the real-world impacts of co-formulants and adjuvants, and points to where future research should be allocated.