The effect of neonicotinoid pesticides on non-target organisms

There is widespread concern over the use of neonicotinoid pesticides in agro-ecosystems, and their effects on the wider environment. This is due in part to their high solubility in water which can lead to widespread contamination of non-target areas including standing surface water, soil, and non-target vegetation. The contribution of neonicotinoid exposure to the ongoing wild pollinator population declines has been the focus of considerable in-depth recent research, focused on the impacts on honeybees, bumblebees, and more recently on solitary bees. However, relatively little research has examined the impacts of exposure on other beneficial non-target organisms. This thesis investigates the impact of field-relevant concentrations of two neonicotinoids: thiamethoxam and clothianidin, on a range of non-model organisms. Model systems were developed for laboratory based experiments on three species: the hoverfly Eristalis tenax; the butterfly Polyommatus icarus; and the earth worm Lumbricus terrestris. A further semi-field experiment investigated the colonisation of contaminated microcosms by aquatic invertebrates. An additional review and analysis of UK time series data tested the relationship between agricultural change (including neonicotinoid usage) and changes in multi-species farmland bird populations. Principally, the results corroborate previous research on non-target organisms and neonicotinoid exposure, showing a negative effect on mortality, food consumption and growth across a range of organisms. Clothianidin decreased the survival of Lumbricus terrestris, exposed via treated soil. Field-realistic exposure also had a significant but temporary effect on food consumption. Sublethal – and sometimes lethal – impacts of clothianidin were also found on the larvae of Polyommatus icarus. Both clothianidin and thiamethoxam showed significant negative effects on Diptera and Ostracoda, with clear differences between the effects of the two chemicals. In contrast, the larval stage of the hoverfly Eristalis tenax was unaffected by field realistic doses of thiamethoxam, with no observed effects on survival or development, nor showed any latent effects on adult activity budgets resulting from exposure to lower concentrations. The re-analysis of the relationship between agricultural change and bird population changes confirmed that evolving agricultural practices continue to affect farmland birds; a moderately significant negative relationship was found between bird population change and neonicotinoid exposure risk. This thesis shows that neonicotinoids have a range of varying and unpredictable negative impacts on diverse invertebrate taxa; and demonstrates that it is possible to develop new model systems to test the effects of pesticides on often-overlooked taxa.