Evaluating the efficacy of entomopathogenic nematodes for the biological control of crop pests: a nonequilibrium approach

The efficacy of entomopathogenic nematodes for biological control is assessed using deterministic models. Typically, the examination of such models involves stability analyses to determine the long-term persistence of control. However, in agricultural systems, control is often needed within a single season. Hence, the transient dynamics of the systems were assessed under specific, short-term control scenarios using stage-structured models. Analyses suggest that preemptive application may be the optimum strategy if nematode mortality rates are low; applying before pest invasion can result in greater control than applying afterward. In addition, repeated applications will suppress a pest, providing the application rate exceeds a threshold. However, the period between applications affects control success, so the economic injury level of the crop and the life history of the pest should be evaluated before deciding the strategy. In all scenarios, the most important parameter influencing control is the transmission rate. These findings are applicable to more traditional biological control agents (e.g., microparasites and parasitoids), and we recommend the approach adopted here when considering their practical use. It is concluded that it is essential to consider the specific crop and pest characteristics and the definition of control success before selecting the appropriate control strategy.     

Host-associated differentiation of target pests should be assessed before using gene drive as a pest control tool − an opinion

Advances in gene editing have made feasible the potential use of gene drive for pest control. Ecological risk assessments will certainly be required before this technology can be released into open fields. In this article, I argue for the importance to include host-associated differentiation (HAD) as part of ecological risk assessment models due to its potential to modulate gene drive spread and risk. Depending on the context, HAD may hamper or facilitate pest control efforts using gene drives. Overlooking HAD may impair pest suppression goals and inflate estimations of effective population sizes, whereas its inclusion within gene drive deployment strategies, as a form of ecological containment, may facilitate gene drive implementation under specific scenarios. Because HAD varies geographically and among closely related species, it will need to be assessed on a case-by-case basis. Failure to incorporate HAD within ecological risk assessment models may undermine pest control goals and diminish the accuracy of estimated ecological risks associated with gene drive releases.     

Multi-Objective Evolutionary Optimization of Biological Pest Control with Impulsive Dynamics in Soybean Crops

The biological pest control in agriculture, an environment-friendly practice, maintains the density of pests below an economic injury level by releasing a suitable quantity of their natural enemies. This work proposes a multi-objective numerical solution to biological pest control for soybean crops, considering both the cost of application of the control action and the cost of economic damages. The system model is nonlinear with impulsive control dynamics, in order to cope more effectively with the actual control action to be applied, which should be performed in a finite number of discrete time instants. The dynamic optimization problem is solved using the NSGA-II, a fast and trustworthy multi-objective genetic algorithm. The results suggest a dual pest control policy, in which the relative price of control action versus the associated additional harvest yield determines the usage of either a low control action strategy or a higher one.     

Management of orthopteran pests: a conservation perspective

Although the vast majority of orthopterans are not pests, some species have the potential to cause serious damage to human interests. Management of pest populations frequently conflicts with conservation of orthopteran species and processes, particularly when the pest species or its ecological processes are susceptible to extinction or when the pest population is coincident with non-target orthopterans. With respect to chemical control, the greatest hazards are the broad-spectrum, highly lethal properties of most agents, which can be mitigated with formulation and application methods. Biological control risks permanent, large-scale changes to orthopteran species and processes which can be minimized with bioinsecticidal and other short-lived or selective formulations and reliable host-range testing. Cultural control may have large-scale, broad-spectrum impacts to non-target orthopterans, but these hazards can be diminished by appropriate testing and monitoring. Mechanical control methods may be impractically labour intensive, but they are highly target specific and therefore warrant further consideration. Social control measures such as education, insurance and compensation programmes appear to have little direct potential for harm to orthopteran conservation, but the complex socioeconomic and, ultimately, environmental consequences of such programmes have not been assessed. The melding of orthopteran pest management and conservation requires that we perceive these insects and their ecological processes to be vital elements of sustainable agroecosystems. Our management of orthopterans (both non-target and pest populations) must focus on keeping good stewards on the land.     

The dynamics of plant disease models with continuous and impulsive cultural control strategies

Plant disease mathematical models including continuous cultural control strategy and impulsive cultural control strategy are proposed and investigated. This novel theoretical framework could result in an objective criterion on how to control plant disease transmission by replanting of healthy plants and removal of infected plants. Firstly, continuous replanting of healthy plants and removing of infected plants is taken. The existence and stability of disease-free equilibrium and positive equilibrium are studied and continuous cultural control strategy is given. Secondly, plant disease model with impulsive replanting of healthy plants and removing of infected plants is also considered. Using Floquet's theorem and small amplitude perturbation, the sufficient conditions under which the infected plant free periodic solution is locally stable are obtained. Moreover, permanence of the system is investigated. Under certain parameter spaces, it is shown that a nontrivial periodic solution emerges via a supercritical bifurcation. Finally, our findings are confirmed by means of numerical simulations. The modeling methods and analytical analysis presented can serve as an integrating measure to identify and design appropriate plant disease control strategies.     

试论拓宽生物防治范围，发展虫害可持续治理

该文针对我国生物防治资源极其丰富和农民经济实力薄弱的特点,结合我国微孢子虫治蝗和苹果园植被多样化持续治理虫害的成果,论述了应如何发展和拓宽具有我国特色的害虫生物防治,进一步提高综合防治水平,促进农业可持续发展。     

我国梨小食心虫综合防治研究进展

近年来,由于农业产业结构的调整,我国北方果树栽培种类日益增多、种植面积不断扩大。重要果树害虫梨小食心虫Grapholitha molesta(Busck)为害大幅回升、危害逐年增加。针对这一情况,在西北、东北和华北3个北方果树生产代表区域建立50余个监测示范点,开展了梨小食心虫的生物生态学规律及综合防治技术的研究、集成与示范。研究结果表明,气候变化和种植结构对梨小食心虫发生规律有显著影响。全球气候变暖条件下,梨小食心虫年发生世代呈增加趋势;在果树混栽区域,晚熟桃为梨小食心虫的主要越冬场所。防治技术方面,在对梨小食心虫常规农业防治、物理防治、生物防治、化学防治技术组装配套的基础上,重点开展了高效节水诱捕器、国产迷向产品研发及标准化应用技术、优势天敌饲养及释放技术、专用农药研发及农药减量化技术等研究工作。前瞻性地研发了植物源诱捕剂及迷向新剂型等贮备技术。最后针对当前梨小食心虫防治工作中存在的问题和不足,确定了下一步的研究方向:(1)全球气候变暖对梨小食心虫发生动态的影响;(2)梨小食心虫成虫不同寄主间的转移规律;(3)梨小食心虫的抗性监测技术和快速诊断试剂盒研制;(4)梨小食心虫的抗性分子机理与抗性治理技术。     

具有阶段结构和群体防卫的脉冲捕食系统

讨论了食饵具有群体防卫和捕食者具有阶段结构的脉冲控制捕食系统,根据Floquet乘子理论和脉冲比较定理,获得了食饵（害虫）灭绝周期解局部稳定与系统持续生存的充分条件．利用Matlab软件对害虫灭绝周期解和害虫周期爆发现象进行了数值模拟,并揭示了诸如高倍周期振荡,混沌,吸引子突变等复杂的动力学现象．得出的结论为害虫治理提供了可靠的策略依据．     

Mechanisms for flowering plants to benefit arthropod natural enemies of insect pests： Prospects for enhanced use in agriculture

Reduction of noncrop habitats, intensive use of pesticides and high levels of disturbance associated with intensive crop production simplify the farming landscape and bring about a sharp decline of biodiversity. This, in turn, weakens the biological control ecosystem service provided by arthropod natural enemies. Strategic use of flowering plants to enhance plant biodiversity in a well-targeted manner can provide natural enemies with food sources and shelter to improve biological control and reduce dependence on chemical pesticides. This article reviews the nutritional value of various types of plant-derived food for natural enemies, possible adverse effects on pest management, and the practical application of flowering plants in orchards, vegetables and field crops, agricultural systems where most research has taken place. Prospects for more effective use of flowering plants to maximize biological control of insect pests in agroecosystem are good but depend up on selection of optimal plant species based on information on the ecological mechanisms by which natural enemies are selectively favored over pest species.     

Optimal HIV treatment by maximising immune response

We present an optimal control model of drug treatment of the human immunodeficiency virus (HIV). Our model is based upon ordinary differential equations that describe the interaction between HIV and the specific immune response as measured by levels of natural killer cells. We establish stability results for the model. We approach the treatment problem by posing it as an optimal control problem in which we maximise the benefit based on levels of healthy CD4+ T cells and immune response cells, less the systemic cost of chemotherapy. We completely characterise the optimal control and compute a numerical solution of the optimality system via analytic continuation.Research supported by the Natural Science and Engineering Research Council (NSERC) and the Mathematics of Information Technology and Complex Systems (MITACS) of Canada     

Optimum timing for integrated pest management: Modelling rates of pesticide application and natural enemy releases

Many factors including pest natural enemy ratios, starting densities, timings of natural enemy releases, dosages and timings of insecticide applications and instantaneous killing rates of pesticides on both pests and natural enemies can affect the success of IPM control programmes. To address how such factors influence successful pest control, hybrid impulsive pest-natural enemy models with different frequencies of pesticide sprays and natural enemy releases were proposed and analyzed. With releasing both more or less frequent than the sprays, a stability threshold condition for a pest eradication periodic solution is provided. Moreover, the effects of times of spraying pesticides (or releasing natural enemies) and control tactics on the threshold condition were investigated with regard to the extent of depression or resurgence resulting from pulses of pesticide applications. Multiple attractors from which the pest population oscillates with different amplitudes can coexist for a wide range of parameters and the switch-like transitions among these attractors showed that varying dosages and frequencies of insecticide applications and the numbers of natural enemies released are crucial. To see how the pesticide applications could be reduced, we developed a model involving periodic releases of natural enemies with chemical control applied only when the densities of the pest reached the given Economic Threshold. The results indicate that the pest outbreak period or frequency largely depends on the initial densities and the control tactics.     

害虫生物防治的数学模型

文章讨论一类捕食者（天敌）具脉冲放养与食饵（害虫）具阶段结构时滞的捕食-食饵模型,得到了害虫灭绝周期解全局吸引的充分条件和害虫的密度可以控制在经济危害水平E（EIL）之下的脉冲存放周期．为现实的害虫管理提供一定的理论依据．     

Excitable Population Dynamics,Biological Control Failure,and Spatiotemporal Pattern Formation in a Model Ecosystem

Biological control has been attracting an increasing attention over the last two decades as an environmentally friendly alternative to the more traditional chemical-based control. In this paper, we address robustness of the biological control strategy with respect to fluctuations in the controlling species density. Specifically, we consider a pest being kept under control by its predator. The predator response is assumed to be of Holling type III, which makes the system’s kinetics “excitable.” The system is studied by means of mathematical modeling and extensive numerical simulations. We show that the system response to perturbations in the predator density can be completely different in spatial and non-spatial systems. In the nonspatial system, an overcritical perturbation of the population density results in a pest outbreak that will eventually decay with time, which can be regarded as a success of the biological control strategy. However, in the spatial system, a similar perturbation can drive the system into a self-sustained regime of spatiotemporal pattern formation with a high pest density, which is clearly a biological control failure. We then identify the parameter range where the biological control can still be successful and describe the corresponding regime of the system dynamics. Finally, we identify the main scenarios of the system response to the population density perturbations and reveal the corresponding structure of the parameter space of the system. A. Morozov is on leave from Shirshov Institute of Oceanology, Russian Academy of Science, Nakhimovsky Prosp. 36, Moscow 117218, Russia.     

Distribution of cryptic blue oat mite species in Australia: current and future climate conditions

• 1 Invertebrate pests, such as blue oat mites Penthaleus spp., cause significant economic damage to agricultural crops in Australia. Climate is a major driver of invertebrate species distributions and climate change is expected to shift pest assemblages and pest prevalence across Australia. At this stage, little is known of how individual species will respond to climate change.
• 2 We have mapped the current distribution for each of the three pest Penthaleus spp. in Australia and built ecological niche models for each species using the correlative modelling software, maxent . Predictor variables useful for describing the climate space of each species were determined and the models were projected into a range of future climate change scenarios to assess how climate change may alter species‐specific distribution patterns in Australia.
• 3 The distributions of the three cryptic Penthaleus spp. are best described with different sets of climatic variables. Suitable climate space for all species decreases under the climate change scenarios investigated in the present study. The models also indicate that the assemblage of Penthaleus spp. is likely to change across Australia, particularly in Western Australia, South Australia and Victoria.
• 4 These results show the distributions of the three Penthaleus spp. are correlated with different climatic variables, and that regional control of mite pests is likely to change in the future. A further understanding of ecological and physiological processes that may influence the distribution and pest status of mites is required.

     

The prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects

In this paper, we consider the prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects. By applying the Floquet theory of linear periodic impulsive equation, we show that there exists a globally asymptotically stable pest-eradication periodic solution when the impulsive period is less than some critical value, that is, the pest population can be eradicated totally. But from the point of ecological balance and saving resources, we only need to control the pest population under the economic threshold level instead of eradicating it totally, and thus, we further prove that the system is uniformly permanent if the impulsive period is larger than some critical value, and meanwhile we also give the conditions for the extinction of one of the two preys and permanence of the remaining species. Thus, we can use the stability of the positive periodic solution and its period to control insect pests at acceptably low levels. Considering population communities always are imbedded in periodically varying environments, and the parameters in ecosystem models may oscillate simultaneously with the periodically varying environments, we add a forcing term into the prey population's intrinsic growth rate. The resulting bifurcation diagrams show that with the varying of parameters, the system experiences process of cycles, periodic windows, periodic-doubling cascade, symmetry breaking bifurcation as well as chaos.     

Plant: soil interactions in temperate multi-cropping production systems

Background and scope

Multi-cropping approaches in production systems, where more than one crop cultivar or species are grown simultaneously, are gaining increased attention and application. Benefits can include increased production, effective pest, disease and weed control, and improved soil health. The effects of such practices on the range of interactions within the plant-soil system are manifest via plant interspecific competition, pest and disease attenuation, soil community composition and structure, nutrient cycling, and soil structural dynamics. Interplant diversity and competition effectively increases the nature and extent of root networks, tending to lead to more efficient resource use in time and space. Increased competitive ability at a system level, and allelopathic interactions, can reduce weed, pest and disease severity. Soil biotic communities are affected by plant diversity, which can increase abundance, diversity and activity of functional groups. Attendant rhizosphere-located processes can facilitate nutrient uptake between component crops. Whilst there are few studies into multi-cropping effects on soil structure, it is hypothesised that such processes are manifest particularly via the role which the belowground biota play in soil structural dynamics. A deeper understanding of eco-physiological processes affecting weed, pest and disease dynamics in the context of multiple cropping scenarios, and breeding cultivars to optimise mutualistic and allelopathic traits of crop mixtures could significantly increase productivity and adoption of more sustainable farming practices.

Conclusions

Wider consideration needs to be given to plant: soil interactions when crop plants are grown in the context of mixtures, i.e. as communities as opposed to monotonous populations. In particular, a better understanding is required of how root systems develop in the context of mixtures and the extent to which resultant interactions with the soil biota are context-dependent. A significant challenge is that crop cultivars or production systems optimised for monocultural circumstances should not be assumed to be most suited for multi-cropping scenarios, and hence alternative strategies for developing new production systems need to take this into account.     

诱集植物在害虫治理中的最新研究进展

诱集植物作为一种传统的害虫治理工具,在农业生产中的应用越来越广泛,其重要性也随着时间推移日益凸显。本文结合国内外研究现状,从特点、应用、优势和发展前景等方面综述了诱集植物在害虫生态控制中的重要作用。同时以香根草为例具体说明了诱集植物的应用方法,为诱集植物的利用与开发提供参考。     

Single species models with logistic growth and dissymmetric impulse dispersal

In this paper, two classes of single-species models with logistic growth and impulse dispersal (or migration) are studied: one model class describes dissymmetric impulsive bi-directional dispersal between two heterogeneous patches; and the other presents a new way of characterizing the aggregate migration of a natural population between two heterogeneous habitat patches, which alternates in direction periodically. In this theoretical study, some very general, weak conditions for the permanence, extinction of these systems, existence, uniqueness and global stability of positive periodic solutions are established by using analysis based on the theory of discrete dynamical systems. From this study, we observe that the dynamical behavior of populations with impulsive dispersal differs greatly from the behavior of models with continuous dispersal. Unlike models where the dispersal is continuous in time, in which the travel losses associated with dispersal make it difficult for such dispersal to evolve e.g., [25], [26], [28], in the present study it was relatively easy for impulsive dispersal to positively affect populations when realistic parameter values were used, and a rich variety of behaviors were possible. From our results, we found impulsive dispersal seems to more nicely model natural dispersal behavior of populations and may be more relevant to the investigation of such behavior in real ecological systems.     

Insects in agroecosystems – an introduction

Agroecology is the study of linkages in agricultural systems and it derives from the need to understand and restore natural connections and ecological complexity to control insect and other pest populations. The present special issue addresses a rich variety of agroecosystems spanning the globe, involving the roles of a range of insects on a great many crops. The overview will further improve our understanding of the complex ecology of the players and the ecological complexity of the crop systems.     

昆虫共生微生物及其功能研究进展

昆虫体内共生微生物能够占到昆虫生物量的1％～10％,主要包括细菌、真菌、古菌和病毒.昆虫与共生微生物共进化形成共生体,共生微生物在昆虫生物学性状、多样性形成、生态适应性与抗逆性等多方面发挥着重要的作用.昆虫中的农作物害虫严重影响农业生产.本文对2000年以来农业害虫共生微生物的多样性、研究方法和功能机制、共生微生物之间...