Agricultural pest insect control: combining genetics, resistance management and dynamics

Lead Research Organisation: University of Exeter
Department Name: Biosciences

Abstract

The public and consumers increasingly want to see more sustainable methods used to control pests and there is general concern to promote sustainability and biodiversity in agricultural ecosystems.
Diamondback moth (DBM) is a major worldwide pest of brassicas (e.g. broccoli, cabbage) causing economic losses of $4-5bn annually through management costs and crop damage. DBM has evolved resistance to all known classes of synthetic chemical insecticides and to at least two bio-pesticides based on Bt, Bacillus thuringiensis. Bt toxins typically have specific action against particular insect Orders (e.g. Lepidoptera), have unparalleled environmental safety and have been widely engineered into transgenic crops. The evolution of resistance to Bt toxins is a real challenge to the sustainable exploitation of this key bio-pesticide. DBM has not only evolved resistance to Bt many times in the field, but is also a proven laboratory system for testing evolutionary theory.
Our industry partner, Oxitec Ltd (an Oxford spin-out), is pioneering genetically engineered "sterile" insects to suppress populations of agricultural or public health pests. Released "RIDL" male insects find mates in the wild and their offspring inherit a genetic construct that prevents them developing to adulthood. Our theoretical work predicts that a female-specific version will not only reduce insect numbers (daughters die so there are fewer females to lay eggs) but also help dilute any resistance in the population (sons inherit Bt-susceptible alleles from released males).
Our cross-disciplinary research project brings together experts in ecology and evolution of the DBM-Bt system and world-leading biotechnologists to explore the management of insect resistance to bio-pesticides and the interplay with genetic insect control.
Novel RIDL strains of DBM will be developed, in addition to Oxitec's prototypes, and a phased series of experiments will be conducted on their biology, genetic traits, and performance for suppressing DBM populations and managing resistance to Bt. Key performance traits include male mating competitiveness, sperm competition with wild-type males, longevity, dispersal, the ability to find mates and suitability for mass-rearing. These will be analysed at increasing levels of detail and realism, from small laboratory cage experiments to experiments in simulated (field cage) and actual field conditions, progressively identifying and prioritizing the most suitable strains.
We will perform a series of experiments involving competition and selection to explore the effect of RIDL male releases on the evolution of DBM resistance to Bt bio-pesticides. The experiments will incorporate key features of existing resistance management strategies, such as Bt-free refuges to provide a source of Bt-susceptible genes alongside Bt diet (this is a key feature of current measures to manage resistance to Bt crops), populations with non-homogeneous spatial structure and various ecological conditions, and mixtures of different toxins (multiple toxins are used in spray treatments and engineered into some plants). These experiments will provide direct tests of theoretical predictions about the evolution of resistance and provide information about the system's dynamics to inform the formulation and parameterization of further mathematical models.
Our empirical experiments will be supported by a range of novel mathematical models to gain a fuller understanding of the bio-economics of integrated pest management approaches combining bio-pesticides with genetic pest control. We will explore the potential cost-effectiveness and policy options for integrated biologically-based management of agricultural pests such as DBM.

Technical Summary

This is a cross-disciplinary collaborative LINK project, with commercial partner Oxitec Ltd, with the objective of optimizing a biotechnological solution for the management of insect resistance to bio-pesticides. We will combine genetic technological developments with mathematical models, laboratory and field experiments to develop an integrated research approach for novel methods of insect pest management.
Oxitec pioneered the development of RIDL - Release of Insects carrying a Dominant Lethal genetic system - a novel approach to insect pest management based on the sterile insect technique.
Oxitec has recently developed transgenic RIDL DBM strains with female-specific lethality. Theoretical modelling has predicted that RIDL releases can mitigate resistance by reducing pest population size and driving pesticide-susceptible genes into a population through the male line.

Our project aims to build on these recent advances. We will test this novel theory using experimental evolution and competition assays to simulate existing resistance management strategies (work packages 1 and 2). We will extend testing to scenarios that are predicted to increase the impact of RIDL releases on resistance management. These scenarios will be increased spatial structure and exposure to multiple toxins. In work package 3 the fitness and field-suitability of new RIDL DBM strains will be investigated through fitness and mating competition assays. Performance of these strains will carefully evaluated in an experimental series that culminates in the field. This will be thoroughly supported by a range of novel mathematical models that will provide a detailed understanding of the evolution of resistance to Bt and its toxins in diverse and heterogeneous agro-ecosytems and also of the cost-effectiveness of genetic control methods for agricultural pests such as DBM (work package 4).

Planned Impact

see lead document

Related Projects

Project Reference Relationship Related To Start End Award Value
BB/L00819X/1 31/03/2014 29/02/2016 £275,764
BB/L00819X/2 Transfer BB/L00819X/1 01/03/2016 31/03/2017 £102,323
 
Description We have investigated experimentally how the release of genetically modified insects might be compatible with the dominant mode of resistance management for genetically modified crops. We have shown that self-limiting GM insects developed by Oxitec can slow or reverse the evolution of resistance and explored the parameter range under which they are compatible. Experiments have shown that moderate release rates and small refugia can work well together btu that impact of the evolution of resistance are critically dependent on the fitness of GM insects and their offspring. Furthermore, we have explored the efficacy of different strategies for GM insect release in structured insect populations and in populations under heterogeneous selection pressure.
Exploitation Route This is the first thorough experimental validation of the value of self-limiting insects insects in resistance management. It confirms that this could be a novel and valuable tool for combating the evolution of resistance and indicates the critical parameters (refuge size, release ratios, transgene fitness costs and their dominance) that are crucial to deploying these tools.
Sectors Agriculture, Food and Drink,Environment

 
Description Helped ADAS draft "Crop Action" document on control of diamondback moth during the 2016 outbreak: issue 29
Geographic Reach National 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Impact We anticipate that advice on the largest influx of a key Brassica pest for 40 years would have had some impact on farmer's ability to control this pest over that season, although these would be very hard to quantify
 
Description Membership of ACRE- DEFRA committee on release of GMOs and biological control agents
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
 
Description Microbial ecology and insect fitness 
Organisation Oxitec Ltd
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Private 
PI Contribution We have produced preliminary data indicating that intestinal microbiota make a significant contribution to insect fitness, especially the ability to compete for mates. This could have significant implications for the Oxitec's technology and plans to release insects for pest population reduction.
Collaborator Contribution The partner Oxitec provided GM insects and made suggestions for protocols/ rearing methods.
Impact At the moment we are considering options for how to follow up on these data- this may mean applying for additional grant/studentship funding.
Start Year 2016
 
Description Open days 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact The Penryn campus runs a series of open days throughtout the year designed to engage with prospective students and their families. This gives us a venue in which to talk about our research generally and that of the campus. In an event last summer, for instance, I discussed the recent invasion of diamond back moth and met with a local cabbage farmer and talked about pest control issues associated with this species.
Year(s) Of Engagement Activity 2016
 
Description Radio interviews relating to diamondback moth outbreak 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact We put out a press release relating to the 2016 diamonndback moth outbreak and since Cornwall is a Brassica growing region and this is a Brassica pest I also directly contacted local radio stations. This lead to a series of radio interviews on BBC Local Radio (Laurence Reed Show); Heart FM and was picked by the Mark Forrester show - a pick of local radio program broadcast nationally.
Year(s) Of Engagement Activity 2016
 
Description Science of Christmas 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact This is a children focussed event designed to build enthusiasm in a young / very young audience for science in general. The event is a series of Christmas themed talks- my contributution discussed gift giving in animals and bacteria and introduced the idea of unwanted presents and also touched on current antiobiotic resistance themes. As well as the regional audience parts of this show received some national media interest.
Year(s) Of Engagement Activity 2016