Understanding the molecular determinants of bee sensitivity to pesticides

Bees are among the world's most environmentally and economically important group of insects, pollinating a remarkable diversity of flowering plants and playing a key role in the production of a wide range of food and commodity crops. However, while carrying out this ecosystem service bees can be exposed to a variety of potentially harmful toxins. These include both natural compounds, such as the defensive chemicals produced by plants, and synthetic compounds such as pesticides. Bees are often considered to be highly sensitive to such toxins, however, they have evolved sophisticated metabolic systems to detoxify many of the natural toxins encountered in their environment. Our recent work on four managed bee species has shown that these biotransformation pathways can also protect bees against certain synthetic insecticides. Specifically, we showed that a small number of bee enzymes belonging to the cytochrome P450 superfamily can efficiently detoxify certain insecticides. However, not all bee species have such P450 enzymes, and we have shown that one species of leafcutter bees that lacks them is thousands of times more sensitive to certain insecticides than other managed bee species that have them. This finding has significant implications for the safe use of insecticides, and thus it is now imperative to understand which species of bees have P450 enzymes that provide protection against certain insecticides and which do not.

This project will address this knowledge gap by harnessing the dramatic increase in genome and transcriptome sequences available for bees to understand the evolution and function of key cytochrome P450 enzyme families in this group of insects. In the first objective of the project we will use a comparative genomic approach (comparing the complement and relationship of P450s in different bee species) to predict which bee species have P450s that are preadapted to detoxify certain insecticides. These predictions will be tested by functionally expressing candidate bee P450s in the laboratory and examining their capacity to detoxify insecticides. Our preliminary work on a managed solitary bee species has identified significant genetic variation in the genes encoding the P450s that metabolise certain insecticides, however, the consequences of this on bee sensitivity to insecticides is unclear. Thus, the second objective of the project will identify genetic variation in insecticide metabolising P450s in a model solitary and social bee species. The consequences of this genetic variation on the ability of the encoded P450s to detoxify insecticides will be established using our functional pipeline. The work conducted in Objective 1 and 2 will provide an extensive dataset on the efficiency of different bee P450 enzymes in metabolising insecticides. In the third objective this will be leveraged to understand why certain P450s can metabolise insecticides but not others. We will identify amino acid residues in bee P450 enzymes that are critical in determining insecticide metabolism and the key structural groups of insecticide chemistry they interact with.

The data generated in this project will fundamentally advance our understanding of the evolution of P450 enzymes in bees, and will have significant applied impact in relation to safeguarding bees from potentially harmful pesticide exposure. A key outcome of the project will be the development of a robust framework that can be used to predict the sensitivity of bee species to existing and future insecticides. This is of value as it can be used to identify pesticide use that poses high risks to bees, and will directly inform the development of more accurate pesticide risk assessment frameworks. Finally, the knowledge and tools generated in the project will greatly accelerate the development of next-generation bee-safe insecticides.

Pesticides continue to play a key role in modern agriculture by controlling plant pests and diseases and securing quality and yield in plant production. However, there is an urgent need to ensure that non-target organisms such as bee pollinators are not harmed by existing pesticides, and develop new compounds that show high efficacy against crop pests but low toxicity to non-target beneficial insects. We have recently demonstrated that some managed bee species have P450 enzymes that provide strong protection against certain insecticides. However, we have also shown that these enzymes are not ubiquitous across all bee species, and that species that lack them can be several orders of magnitude more sensitive to certain insecticides. Thus it is now imperative to understand which species of bees have P450 enzymes that can detoxify insecticides and which do not. This project will meet this need by characterising the evolution and function of key P450 subfamilies in bees and developing a robust framework that can be used to predict the sensitivity of bee species to existing and future insecticides. We will use genomic and functional approaches to: a) Understand how P450s involved in detoxification have evolved across bee pollinators, and which bee species encompassing key bee genera have P450s that metabolise insecticides, b) characterise the level of genetic variation in key P450 subfamilies within model bee populations and how this affects insecticide metabolism, and c) identify key structure/function determinants of bee P450/insecticide interactions, i.e. which amino acid residues in bee P450s are critical in determining insecticide metabolism and which structural groups of insecticide chemistry they interact with. The knowledge generated will allow us to predict and avoid negative outcomes of pesticide use, inform the development of robust pesticide risk assessment frameworks for bees, and facilitate the development of next-generation bee-safe insecticides.