Effects of Neonicotinoid Pesticides on Bumblebee Social Behaviour

Abstract

Social bees are the single most important group of pollinators, yet many populations are in decline and human activity is the likely cause. In agricultural landscapes, pollinating bees are unintentionally exposed to a diverse cocktail of chemical pesticides; such exposure is thought to be a significant driver in the decline of bee populations worldwide. Systemic neonicotinoid pesticides are of particular concern because they are widely used and they have a direct route of exposure to bees via the nectar and pollen of treated crops. Field-realistic sub-lethal doses of these insecticides disrupt nerve cells in the bee brain, leading to effects on individual behaviour and colony productivity. These effects are well described, but we do not understand the mechanisms by which effects on individuals scale up to colony-level failure. This thesis shows that social context modulates neonicotinoid-induced behavioural impairments in bumblebees (Bombus terrestris) and that colonies exhibit a certain level of resilience that could not have been predicted based on individual responses alone. High-throughput automated behavioural monitoring revealed that the movement speeds of bees decreased, but bees tended to cluster together to maintain social interaction rates. The nest behaviour of active foragers (relative to non-foraging workers) showed the greatest susceptibility to toxic effects and did not recover post- exposure. However, total colony-level foraging effort remained relatively unchanged. Foragers also showed normal interactions patterns with non- foragers and temporal network flow simulations suggested this would maintain information flow across the colony. Additionally, behaviourally dominant bees seemed to be relatively more strongly affected, but again, group-level social organisation (dominance hierarchy formation) was not affected. These results demonstrate the importance of assessing the risks of pesticide exposure to bumblebees in a social context. Furthermore, the emergence of social organisation through the self-organising patterns of pair- wise interactions may be a key mechanism providing social resilience to pesticides. Understanding the responses of complex social systems, as found in insect societies, is vital to predicting how insects will cope with increasing agricultural intensification.

Date of Award	23 Jan 2019
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Jane Memmott (Supervisor), Seirian Sumner (Supervisor) & Richard James (Supervisor)