From pesticides to pollination: Conserving beneficial insects in agroecosystems

Beneficial invertebrates are essential to healthy ecosystem functioning. In particular, pollinators and natural enemies provide economically valuable services in agro-ecosystems, through improving yields when pollinating important crops, and suppressing crop pests that may cause economic damage. Agricultural intensification, including the widespread use of pesticides, poses challenges to pollinator and natural enemy communities, many of which are facing population declines. The aim of this thesis was to assess the risk of exposure to beneficial communities in agriculture and examine the potential hazards of pesticides to pollinators, specifically bees.
Visiting several mass-flowering crop fields (oilseed rape, Brassica napus), I surveyed beneficial pollinator and natural enemy communities between winter and spring sown varieties, which differ in their flowering phenology (early and late flowering). I found that pollinator communities differed in abundance, diversity and composition between the two crop types and that natural enemies (carabid beetles and spiders) only differed in community composition. Using spray information for each field, I estimated that all beneficial communities are at risk of pesticide exposure in winter and spring oilseed rape, and that most of this risk occurs around the time of peak flowering. I then focussed on bees, due to their importance as pollinators, and investigated the potential hazards that widely used pesticides may impose if bees were to be exposed in the field. I conducted a laboratory study to investigate the potential implications of exposure to field realistic concentrations of a fungicide, insecticide and combination, on queen bumblebees (Bombus terrestris). I found that exposure did not affect the diapause survival of queens, but the insecticide treatment before and after diapause found negative effects on queen longevity and colony development. In my final two experiments, I used a cage study design to investigate the potential effects of insecticide exposure on the foraging behaviour and pollination service delivery of solitary mason bees (Osmia bicornis) and bumblebees (Bombus terrestris). Bumblebee foraging behaviour did not differ at the individual level, nor did their pollination of potted oilseed rape, however, insecticides altered colony activity and the return of pollen provisions to the nest by workers. In contrast, solitary bee foraging behaviour was altered by pesticide exposure in addition to their delivery of pollination services depending on the number of chemical exposures they received. In all three of these laboratory and cage experiments, I found that insecticide-driven effects may differ depending on the bee taxa and the chemical class. Finally, I conclude with a synthesis of results and some methodological considerations. I propose some suggestions for the management of crop pollination services and recommendations for improvements of pesticide risk assessments and regulatory testing. I also highlight some potential areas for further research.