An investigation into the synergistic impact of sublethal exposure to industrial chemicals on the learning capacity and performance of bees

The continual pressure for increased efficiency that has driven the spread of large crop monocultures has in turn increased the risk of pest damage to crops and driven down the density and diversity of natural pollinators and predators. As a result, we find ourselves critically dependent upon pesticides to protect vulnerable crops and the bees to pollinate them. Honeybee populations worldwide are in crisis and bumblebees species and populations are in decline. For honeybees, identified threats include changing climatic conditions and attack by various mites and diseases. Exposure to the varied cocktail of pesticides upon which we rely to protect crops could also be harming beneficial pollinators. Ironically, the miticides used to protect honeybees from mites may also be harmful to bees. The nervous system of all animals operates by the rapid transmission of information between brain cells (neurons) across the brain. Neurons communicate using chemical messengers (e.g. acetylcholine, ACh), to which a neighbouring neuron responds using specific receptors (e.g. ACh receptors, AChRs). To ensure that the message is received only once, excess ACh is rapidly inactivated. The recipient neuron passes this information on to the next neuron and so information spreads rapidly across the brain. This 'excitatory' brain activity is tempered by opposing (inhibitory) activity, whereby some neurons do not respond. Balancing these two opposing signals provides control and limits dangerous hyperactivity in the brain. Many pesticides act by interfering with information flow in the insect brain. Some increase ACh release, or inhibit its removal, while others directly stimulate AChRs or remove the brake by blocking the inhibition. Collectively and at sub-toxic levels, pesticides may act together to alter brain activity as seen for two miticides; Checkmite and Apistan. At low levels, pesticides might trigger hyperactivity to initiate epileptic seizures, mood disorders or altered learning and memory. These sub-toxic effects are poorly understood and the potential for synergy between pesticides is largely unknown. We hypothesise that the chronic exposure of honeybees to miticides combines with sub-toxic agricultural pesticides to disturb critical bee behaviours such as foraging, navigation and communication. Understanding the molecular mechanisms involved in potential synergistic actions of pesticides on behaviour requires a simplified, yet robust, model. To achieve this, we will perform studies directly on neurons purified from bee brains and cultured in the laboratory. These cultures will be used to analyse neuronal responses to pesticides, both alone and in combination. For more long-term and widespread utility (screening and monitoring), we propose to develop novel honeybee cell lines. Results from the neuronal screening approach will be validated using brain slices to monitor electrical brain activity. Using these techniques, we can study the molecular basis of learning and memory and how this is affected by pesticide exposure. To explore the consequences of combined sub-toxic exposures on honeybee and bumblebee health we will investigate their ability to perform learning tasks. We will also assess their navigation, foraging and communication skills using a range of techniques including radio frequency identification tagging of individual bees and decoding the honeybee waggle dance. In addition, we will work in partnership with the Scottish Beekeepers Association (SBA) on a 3-year survey of the impact of environmental chemicals on colony performance. SBA members will also support our data collection with regard to honeybee foraging. This project is a unique opportunity to develop a network of UK scientists with complementary skills and shared goals to address the issues of insect pollinator loss.

Many industrial and household pesticides act on the insect nervous system. However, significant 'off-target' toxicity can also occur in beneficial insects, including bees. The major classes of nervous system insecticide used in the UK act on synaptic transmission. They include potentiation of voltage-gated sodium channels (pyrethroids), inhibition of acetylcholinesterase (organophosphates & carbamates), activation of nicotinic acetylcholine receptors (neonicotinoids) or blocking inhibitory receptor function (thymol, fipronil, avermectins). If present in combination, such agents have potential for additive or synergistic effects. Similarly, fungicides and herbicides have been reported to exhibit unexplained synergy with insecticides. Our multi-disciplinary study will investigate the potential synergistic interactions of industrial agents on bee health using a diverse range of experimental approaches. At the molecular level, quantitative fluorescence assays will use medium throughput screening of cultured bee brain neurons to investigate interactions at the cellular level. These studies will be complemented by brain slice electrophysiology to investigate interactions at the neural network level and the consequences for synaptic plasticity. Results from these screening techniques will feed into behavioural tests of individuals and colonies using a range of learning paradigms in both honeybees and bumblebees. Potential effects of pesticide exposure on bee locomotion, foraging ability and navigation will be determined in laboratory and field experiments. Information generated by the coordinated efforts of all 5 laboratories will be augmented by a survey of experienced amateur beekeepers. Results from this programme will contribute significantly to the development of a co-ordinated strategy on pesticide use to minimise harmful effects to bees. Finally, we aim to develop several bee cell lines that are desperately needed for the rapid screening of future pesticides.

Our goal is to obtain a better understanding of factors contributing to the decline in insect pollinators, including native pollinators such as bumblebees and cultivated honeybees. Success in this goal will have a profound impact on agriculture and in sustaining agricultural diversity. It is hard to overstate the importance of insect pollinators such as bees. It has been estimated that pollination by managed honeybees contributes £165 million per year to the UK economy. Given that many wildflowers also rely on native insect pollinators, our research will also have an impact on environmental biodiversity and food security. Success in reversing the decline in insect pollinators will have widespread benefits, from commercial farming to domestic honey production by amateur beekeepers. Preservation of insect pollinator density and diversity will have a major impact on UK food yields and economic strength. It is hoped that the information generated from this study will enable strategic decisions to be taken with respect to the development of a coordinated policy on the local use of pesticides. Such policies may empower local authorities to orchestrate the use of diverse pesticides with the intention of maximising their effectiveness, whilst limiting their potential for additive toxicity on non-target species, such as bees. We will also provide advice for beekeepers on best practice of the administration of miticides, from the point of view of minimising potential synergistic effects with the most commonly encountered agricultural and domestic pesticides. It is hoped that the initiation of such policy planning will be provoked by our findings within 5 years. A timely response is essential given the consequences of a continued decline in bee populations. Our research may reveal that pesticides do not appear to contribute significantly to bee species decline. Nevertheless, our contribution to the knowledge base will be both significant and valuable. Furthermore, we will have formed a new research network bridging the gap between molecular neuroscience and ecology, which will provide a driving force to facilitate the advancement of our understanding of insect pollinators in the environment. If we identify major synergistic interactions between miticides and pesticides, these would have an immediate impact on our economy and food security. Moreover, novel synergistic interactions amongst household pesticides could also have significant implications for human health should they also occur in mammals. There are also implications for synergistic interactions that may occur between multiple natural toxins (possibly interacting with pesticides) produced by toxic blooms of algae and cyanobacteria. These blooms are becoming increasingly common as a result of climate change and may become a major environmental challenge in the future. Key outputs from this research will be the production of novel honeybee cell lines and the publication of our findings in international peer-reviewed journals. The provision of cell lines for screening was a goal that was encouraged at the Insect Pollinator Initiative meeting. To ensure rapid dissemination of our published findings, the applicants will engage the public via University and funding agency press Offices and by presentations to the general public in Dundee, Newcastle and London. We also plan to deliver our findings directly to our collaborators, the Scottish Beekeepers Association (SBA). Results obtained from the SBA surveys will be collated on a yearly basis and a summary will be posted on the SBA's website for open access. With the SBA so intimately involved in this project, they will be perfectly placed to disseminate advice among their ~1000 members particularly with regard to any miticide contribution to the current honeybee problems.