Understanding the evolution of insecticide resistance in Brazilian crop pests: Towards effective Insecticide Resistance Management (IRM)

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Insect pests represent a major threat to current and future food security with an average of 20% of crops worldwide lost annually to herbivorous insects. This issue is particularly acute in Brazil where agriculture forms a key component of the economy accounting for 26% of gross domestic product (GDP). Synthetic insecticides are widely used by farmers and growers in Brazil in an attempt to reduce yield loss from insect pests. Unfortunately, the growing reliance on insecticides has resulted in the emergence of insect pest populations that are resistant to many of the chemicals used for control. Two of the most economically important species in this regard are the neotropical brown stink bug, Euschistus heros, and the fall armyworm, Spodoptera frugiperda. E. heros is a major pest of soybean and vegetable crops and causes severe damage to cotton and maize, while S. frugiperda feeds on more than 80 plant species but is particularly destructive on maize. Resistance to several important insecticides has now emerged in these species and threatens their sustainable control. Despite the seriousness of this issue very little research has been carried out to understand the evolution of resistance in E. heros and S. frugiperda and to use this knowledge to develop means to combat its emergence and spread. This is, in part, due to a lack of genomic resources for these key pest species - particularly in the case of E. heros. This project builds on key 'omic' (genomic and transcriptomic) and biological resources for E. heros and S. frugiperda generated in a stage 1 pump-prime project to understand the molecular basis of resistance in the two pest species. Specifically, we generated a high quality draft genome sequence of E. heros and strains of E. heros and S. frugiperda that share a common genetic background but differ in their susceptibility to several insecticides. These resources will be exploited in the stage 2 project to identify candidate genes and genetic variation associated with resistance and their causal role validated using transgenic approaches. Understanding the role of these genes in resistance will be facilitated by the generation of gene expression atlases for both species which will comprise databases and user-friendly web applications for studying the expression of genes in different tissues of adults or larvae. These resources will be used in the project to identify where candidate resistance genes are expressed in order to understand how they confer resistance. More broadly their publication will accelerate broad functional genomic research in these pest species beyond the scope of this project. Another key output of the stage 1 project was characterisation of the microbial community (the microbiome) present in the gut of both pest species and the identification of gut bacteria that degrade pesticides. The genomic and biological material generated will be used in the stage 2 project to understand how and to what extent these microbes contribute to resistance, and how they might be disrupted in order to overcome resistance.The data from these experiments will fundamentally advance our understanding of how insects evolve resistance to insecticides. Furthermore, the knowledge generated will be of direct applied importance in relation to the sustainable control of both pest species. To translate the knowledge gained in this project to combat resistance we will develop simple DNA-based diagnostics, and use these to determine the frequency and distribution of resistance in the field in order to inform rational control decisions and develop insecticide resistance management strategies. Furthermore, we will develop screening tools (recombinant enzyme assays or transgenic insect lines) that can be used by academia and industry to develop resistance-breaking chemistry.