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

公众和消费者越来越希望看到更可持续的方法来控制害虫，人们普遍关注促进农业生态系统的可持续性和生物多样性。小菜蛾(DBM)是甘蓝(如西兰花、卷心菜)的一种世界性主要害虫，每年因管理成本和作物损害而造成40-50亿美元的经济损失。DBM已经进化出对所有已知类别的合成化学杀虫剂以及至少两种以苏云金芽孢杆菌为基础的生物杀虫剂的抗药性。Bt毒素通常对特定的昆虫目(如鳞翅目)具有特定的作用，具有无与伦比的环境安全性，并已被广泛应用于转基因作物。对Bt毒素的抗药性的演变对这种关键生物杀虫剂的可持续开发是一个真正的挑战。DBM不仅在田间多次进化出对Bt的抗药性，而且还是一个经过验证的用于测试进化理论的实验室系统。我们的行业合作伙伴Oxitec有限公司(牛津大学的一个分支机构)正在率先开发转基因“不育”昆虫，以抑制农业或公共卫生害虫的数量。被释放的“RIDL”雄性昆虫在野外寻找配偶，它们的后代继承了阻止它们发育到成年的基因结构。我们的理论工作预测，雌性特有的版本不仅将减少昆虫的数量(女儿死亡，因此产卵的雌性更少)，还有助于稀释种群中的任何抗性(儿子从释放的雄性中继承Bt敏感等位基因)。我们的跨学科研究项目汇集了DBM-Bt系统的生态学和进化专家以及世界领先的生物技术专家，以探索昆虫对生物杀虫剂的抗性管理以及与基因控制的相互作用。除了Oxitec的原型外，还将开发新的DBM RIDL菌株，并将对它们的生物学、遗传特性、以及抑制DBM种群和管理对Bt的抗性的性能。关键的性能特征包括雄性交配竞争力、与野生型雄性的精子竞争、寿命、传播性、寻找配偶的能力以及是否适合大规模饲养。这些分析将越来越详细和真实，从小型实验室笼子实验到模拟(田间笼子)和实际田间条件下的实验，逐步确定和优先选择最合适的品系。我们将进行一系列涉及竞争和选择的实验，以探索RIDL雄性释放对DBM对Bt生物杀虫剂抗性进化的影响。这些实验将纳入现有抗性管理策略的主要特征，例如无Bt避难所，以提供Bt敏感基因源和Bt饮食(这是目前管理Bt作物抗性的措施的关键特征)，空间结构和生态条件不同的种群，以及不同毒素的混合(在喷雾处理中使用多种毒素，并将其改造到一些植物中)。这些实验将提供关于抗性进化的理论预测的直接测试，并提供关于系统动态的信息，以便为进一步的数学模型的制定和参数化提供信息。我们的经验实验将得到一系列新的数学模型的支持，以更全面地了解结合生物农药和遗传防治的害虫综合治理方法的生物经济学。我们将探索以生物为基础的农业害虫综合管理的潜在成本效益和政策选择，如DBM。

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.