Understanding resistance of key crop pests in Brazil

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 22% 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 Stage 1 pump-prime project has two aims, firstly it will generate key 'omic' (genomic and transcriptomic) resources and data for E. heros and S. frugiperda that will be a valuable asset to the community studying these species. These will include the first annotated draft genome for E. heros, sequence characterization of the entire microbial community (the microbiome) in the gut of E. heros and S. frugiperda, and tissue-specific gene expression data for both species that can be used to determine where candidate genes (such as those involved in resistance) are expressed. In the context of this proposal these data will greatly facilitate future characterization of genes and DNA markers associated with insecticide resistance in these species that can be used to develop tools to prevent, slow or overcome the development of resistance.

To ensure that the knowledge gained in this and follow on projects can achieve applied impact the second main aim of this pump-prime project is to develop a network of key stakeholder groups in Brazilian agriculture. This will be achieved by holding workshops with members of growers associations, government and industry including representatives of Insecticide Resistance Action Committee Brazil (IRAC-BR), the Brazilian Cotton Growers Association (ABRAPA), the Soybean and Maize Growers Association (APROSOJA), the Brazilian Ministry of Agriculture and the Technical Advisory Committee of Pesticides (CTA). These meetings will define the priorities of future research and develop routes for translation of the science into tools and strategies for resistance management and rational control of these two important insect pests of Brazilian agri-ecosystems.

The proposed research will be of direct and indirect benefit to several groups and end-users beyond the academic community. By providing underpinning resources and data to facilitate characterisation of the mechanisms of insecticide resistance in two highly damaging insect pests of some of the most economically important crops in Brazil, a primary beneficiary will be Brazilian agriculture. An improved understanding of the molecular basis of insecticide resistance (which detoxifying enzymes and target-site mutations confer insecticide resistance and to which chemical classes) will assist with anticipating resistance risks and cross-resistance profiles, and will thereby influence the design and monitoring of strategies for managing these pests while reducing selection pressure for specific resistance mechanisms. Furthermore the future translation of the knowledge generated in this project into tools that can be used to rapidly determine the frequency and distribution of resistance will help growers make rational control decisions. Farmers in other countries where these insects have recently emerged will also benefit from this work. For example the emergence of S. frugiperda in Africa represents a serious threat to maize, the most widely grown crop in Africa and a staple for around half the continent's people. The development of resistance management strategies in Brazil will provide a model that, with modification, would also assist stakeholders in affected African countries to prevent or slow the development of resistance.

The longer term goals of this proposal have additional benefits beyond those relating solely to the control of the target insect pests. Ineffective control due to resistance can result in the wasteful over-application of ineffective compounds leading to negative environmental and economic outcomes. The future development of diagnostics for specific resistance mechanisms will allow resistance to be detected at an early stage and avoid these off-target effects.

Another key beneficiary of our work is the agrochemical industry who recognise the responsibility of stewardship of current actives and are keen to prolong the life of these insecticides. The knowledge and deliverables derived from our study will inform the policy of IRAC (Insecticide Resistance Action Committee) international that works as a worldwide specialist technical group of the industry association CropLife providing a coordinated industry response to prevent or delay the development of resistance in insect and mite pests, and its national body in Brazil (IRAC-BR).

We envisage that a further impact of our research will be its potential influence on the policy and regulatory environment of insecticide registration and use. The ultimate outcomes of our work will be of direct relevance in defining which chemistry should be used for control of these species and how (i.e. how frequently, when and in combination with which other controls). A robust regulatory framework is extremely important in ensuring compliance with strategies that aim to manage resistance and extend the life-span of insecticides that retain efficacy.

The sequencing of a draft genome for E. heros and tissue-specific expression data for E. heros and S. frugiperda as part of this project has significant scope to result in wide ranging impacts beyond managing resistance. Many of the genes identified and annotated in the genome and transcriptomes represent potential targets for novel control strategies and their sequence characterisation is a prerequisite for strategies based on gene knockdown (RNAi) or genetic manipulation (i.e. gene drives). In the same way characterisation of the gut microbiome of these species and understanding the metabolic activity of these herbivore-associated microbes may assist in industrial development of novel pest-management strategies or may have application for biotechnological applications.