农业景观生物多样性与害虫生态控制

现代农业的一个重要特征就是人类对农田生态系统的干扰强度及频率不断增加,严重影响农业景观的结构及其生物多样性.农业景观结构的变化及其生物多样性的丧失,必然引起生态系统服务功能的弱化,不利于实施以保护自然天敌为主的害虫生态控制.农业的集约化经营导致自然生境破碎化,减少了农业景观的复杂性,使得作物和非作物变成一种相对离散化的生境类型和镶嵌的景观格局;破碎化的生境不仅会减少某些物种的丰度,还会影响物种之间的相互关系及生物群落的多样性和稳定性.非作物生境类型如林地、灌木篱墙、田块边缘区、休耕地和草地等,是一种比较稳定的异质化环境.非作物生境较少受到干扰,可以为寄生性和捕食性节肢动物提供适宜的越冬或避难场所以及替代猎物、花粉和花蜜等资源,因此,非作物生境有利于自然天敌的栖息和繁衍,也有利于它们迁入邻近的作物生境中对害虫起到调节和控制作用.景观的格局-过程-尺度影响农田生物群落物种丰富度、多度、多样性以及害虫与天敌之间的相互作用.从区域农业景观系统的角度出发,运用景观生态学的理论和方法来研究作物、害虫、天敌等组分在不同斑块之间的转移过程和变化规律,揭示害虫在较大尺度和具有异质性的空间范围内的灾变机理,可为利用农业景观生物多样性来保护农田自然天敌,实施害虫的区域性生态控制提供新的研究思路和手段.     

农田非作物生境调控与害虫综合治理

就害虫综合治理的研究而言,农田生态系统可以区分出作物生境和邻近作物的非作物生境。昆虫从作物生境迁移到非作物生境,与作物生境缺乏食物或受人类栽培活动干扰而引起的自然迁移、转换寄主和寻求庇护场所有关。许多研究表明,与特定作物田块相联系的植被类型和结构可影响害虫及其天敌迁居的种类、数量和时间。因此,我们可以通过改变大田周围非作物生境的植被组成及特征来调控农业生态系统中害虫与天敌的相互关系,提高天敌对害虫的控制效能。由于景观的空间格局对节肢动物的生物学特性有直接或间接的影响,所以,以景观为单元要比以同类作物的田块为单元更加适于害虫综合治理的研究和实施。在现代农业景观区域内重新引入和相嵌一些非栽培植物或廊道,可为众多有益节肢动物的繁殖、取食和避害提供多种类型的非作物栖境。     

农业活动及转基因作物对农田生物多样性的影响

农田生物多样性是生态系统生物多样性的重要组成部分,但较少受到关注.近50年来,由于农业活动引起的环境污染、生境破碎和单一化种植等严重威胁着农田生物多样性.为了了解各因素对农田生物多样性的影响程度,优化农田管理措施,以提高农作物产量并降低环境影响,本文综述了种植方式、地膜覆盖、农药和化肥使用等农业活动及转基因作物对我国农田生物多样性的影响.农药和化肥的过度使用对农田生物多样性的影响最大;而转基因作物对农田生物多样性的影响受诸多因素影响,如携带的转基因性状等.需要加强转基因作物生态环境影响评价研究,特别是对农田生物多样性的潜在影响.农业生产活动应当与农田生物多样性保护密切结合,不仅有利于提高农作物产量,同时也可减少对环境的负面影响.     

利用生物多样性控制作物害虫的理论与实践

生物多样性是人类可持续发展的重要基础,保护和利用生物多样性是国际社会普遍关注的问题。近年来,通过改善农田生物多样性和强化农田生态系统保益控害的服务功能,实现作物病虫害生态调控已成为国内外研究的热点。本文在总结分析国内外利用生物多样性控制害虫理论研究和实际应用的基础上,综述了该领域的研究进展、实践成果和发展前景。文中介绍了生物多样性的基本概念及其与害虫综合治理的关系,系统概述了利用农田生物多样性控制作物害虫的各种理论假说,包括天敌假说、资源集中假说、联合抗性假说、"推-拉"假说、中度复杂假说、景观缓冲假说等;从提高天敌多样性、作物多样性、非作物多样性和景观多样性等方面综合评述了利用农田生物多样性控制作物害虫的应用实践,重点介绍了我国的一些典型的实际应用案例,旨在充分展示中国昆虫学科技工作者在该领域做出的贡献;针对现代农业集约化经营导致农田生态系统结构简单、农田生物多样性不断下降等特点,对如何以农田景观为单元进一步做好利用生物多样性控制作物害虫的理论研究和应用实践进行了讨论和展望。     

基于服务功能的昆虫生态调控理论

鉴于昆虫在植物传粉授精、害虫生物控制、土壤有机物分解中提供多种生态系统服务功能,本文在害虫生态调控、区域性害虫生态调控与生境管理的基础上,进一步提出基于多种生态服务功能的农田景观昆虫生态调控理论、方法与实践。认为:昆虫管理不仅仅是害虫的管理,还应包括有益昆虫(如传粉昆虫、天敌昆虫、分解昆虫)的管理,这种管理应从单一农田生态系统扩展到农田景观生态系统,充分考虑农田景观中昆虫的传粉功能、生物控害功能和分解功能,通过对功能植物、作物与非作物生境的空间布局以及时间序列上的生态设计,从空间上明确昆虫(包括害虫、天敌、传粉昆虫、分解昆虫)在不同生境中的转移扩散动态,从时间上掌握昆虫在不同寄主植物与非作物生境上的演替过程,从技术上着重发挥有利于昆虫的传粉功能、生物控害功能和分解功能的综合措施,在研究方法上突出使用稳定同位素、生态能量学、化学生态学等定量分析手段,研究景观区域内中"植物-昆虫"互作过程及其生态调控措施的作用,寻求不同时空条件下控害保益的关键措施,设计和组装出维持多功能的农田景观昆虫生态调控技术体系,创造有利于天敌控害、蜜蜂传粉、土壤分解的环境条件,以发挥昆虫类群在农田景观中最大的生态服务功能。     

多尺度空间下害虫生态调控理论与应用

不同尺度空间下农田生态系统具有不同的生境斑块组成结构,尺度性也是生态系统的重要特征之一.近年来,北美和欧洲等地区用农田生境管理与区域性景观设计相结合的研究方法实施多尺度空间下害虫生态调控,实现复合生态系统服务.其核心思想是以大区域景观设计和农田作物布局与农事管理的有机结合,通过农业景观格局的空间配置,调节种植模式、管理技术、乃至改变农业景观格局的空间配置等以切断害虫种群的生活史,建立和恢复天敌种群库与转移通道,从而最大程度地提高农业生态系统自身的控害功能.近年来,北美和欧洲对多尺度空间下农业复合生态系统服务功能都做了大量工作,尤其是田间尺度与景观尺度相结合的研究方法更是当前生境管理研究的重要内容.本文总结了多尺度空间下生态系统环境条件与天敌种群间的作用机制及假说,包括田间尺度上主要通过轮作与间套作、覆盖作物、减免耕及发展有机农业等方式提高天敌种群,景观尺度上通过生境斑块的空间配置来改变植物资源布局,最终提高天敌的控害作用.以期为深入地解析景观格局及复杂性对生物多样性的影响,揭示农业景观变化对昆虫种间关系的作用机制,在实践上为利用农田景观格局控制害虫种群发生提供新的途径与方法.     

半自然农田边界与相邻农田步甲和蜘蛛的时空分布

分别于小麦、玉米收获前后,采用陷阱法调查了华北地区典型农业景观中具有不同植被结构的农田边界及其相邻农田中两类重要天敌类群步甲和蜘蛛的多样性.通过比较农田生境及相邻农田边界间两类天敌群落的时空分布格局及其与相邻半自然生境植被群落的相关关系,探讨半自然农田边界对两类天敌类群的保护作用.结果表明: 整个取样季节农田边界处蜘蛛的多度显著高于农田内部;而步甲多样性在农田与边界间无显著性差异,仅呈现不同的群落结构;作物收获后蜘蛛分科数在边界处的增加以及在农田的减少,显示了蜘蛛在农田和边界之间的迁移活动.边界植被结构对蜘蛛和步甲多样性有不同影响:边界较高的草本层盖度和较低的乔木层盖度有利于增加农田中某些步甲优势种的多样性;而较高的草本层盖度有利于增加皿蛛科蜘蛛的多样性.因此,半自然生境的存在可以通过天敌在农田和边界之间的迁移运动促进农田天敌多样性的维持;但不同类型半自然生境植被群落结构可能影响其对不同天敌群落多样性的维持和保护作用.为促进农业景观对天敌的保护作用,提高其害虫控制功能,需要深入了解不同天敌的生境需求及食物需求,精心设计有利于天敌多样性维持的半自然生境.     

农田景观格局变化对昆虫的生态学效应

景观格局变化是全球变化的一个重要内容。农田是由人类赖以生存所种植的人工栽培作物组成的生态系统。在该景观系统中,多种植物-害虫-天敌相互作用、相互制约,形成有机整体。研究农田景观格局对害虫和天敌种群动态影响,不仅在害虫生物防治的实践中有重要意义,而且对于揭示人类活动对生物多样性结构与功能的影响,阐明农田景观中生物多样性整合、维持机理有重大的理论意义。本文从农田景观格局的"质、量、形、度"4个方面,系统地论述了农田景观格局变化对害虫和天敌的作用,分析了农田景观的生物控制服务功能,指出了未来研究发展的方向。     

农业生物多样性控制作物病虫害的方法与原理

农业生物多样性作为一种重要的作物病虫害防治手段,主要基于自然界生物间相生相克的平衡关系,充分利用了原生态的各种控制因子,将病虫害调控在生产可允许范围,对减肥减药以及提高农业生态系统自我功能具有重要的意义。本文将农业病虫害发生融为一体,从种内遗传多样性、物种多样性、农田景观多样性3个层次,系统阐述了利用农业生物多样性控制作物病虫害的重要意义、主要内容和方法、控害原理、影响因素以及作物品种多样性种植的增产效应,为充分发挥农业生物多样性调控作物病虫害提供参考。     

生境管理——保护性生物防治的发展方向

生境管理是近年来保护性生物防治的重要研究方向,也是利用农业景观格局进行生物防治的重要策略。生境管理是指从农田景观的角度,在大时空尺度范围内进行多种作物与非作物生境的设计与布局,创造有利于天敌的环境条件,抑制害虫种群发生,达到减小环境污染、增强农业生态系统的控害保益功能,最终实现害虫种群控制的可持续性。景观尺度下的生境管理不仅强调单一农田生物控害作用,而是以多生境农业景观整体布局为指导,探索各种生境功能的整合利用,以发挥各种生境最大的生物控害潜能,为实现多目标生态服务价值管理提供重要的理论基础和现实依据。本文系统地总结了生境管理的研究内容与实现途径,论述了农业景观格局与过程对害虫种群控制的机理,并对作为保护性生物防治发展方向的生境管理研究趋势进行了展望。     

Entomofauna associated to horticultural crops under organic and conventional practices in Córdoba, Argentina

Farming practices and the addition of chemical synthetic substances in conventional agroecosystems are detrimental mainly to natural enemies of phytophagous insects, diminishing the natural regulation of pest insects. On the other hand, in organic agriculture, biological processes and care of the environment are favoured, hence an increase in insect biodiversity is predicted in this type of systems. In this work, abundance, richness of insects and proportion of functional groups were compared through a single quantitative sampling of insects in horticultural crop fields, three under organic and three under conventional management practices. Insect species richness, total and for guilds (phytophagous and entomophagous insects) were significantly higher in organic orchards, and also was the abundance of entomophagous insects. Richness and abundance of all insect orders (with exception of Homoptera abundance), were higher in orchards under organic management, being significative the differences for richness of Coleoptera and richness and abundance of Hymenoptera. Similar tendencies were observed in data obtained through sweep net in weeds. These results suggest that organic practices increase the diversity of species, particularly that of natural enemies.     

Diversity and abundance of lepidopteran stem borers and their host plants in Ethiopia

Lepidopteran stem borers are among the most important insect pests of maize, sorghum and sugarcane in sub‐Saharan Africa. Except for Chilo partellus, the other stem borer pests in Ethiopia are indigenous to Africa and are assumed to have coevolved with some native grasses and sedges in the natural habitat. In addition to pest species, natural habitats harbour diverse non‐economic stem borer species, some of which are new to science. However, with the growing threats to natural habitats, some non‐economic stem borer species may switch or expand their host ranges to include cultivated crops and evolve as “new” pests. Besides host switch, some of the unknown species currently limited to natural habitats may disappear. We examined the diversity, abundance and interactions of lepidopteran stem borers and their wild host plants in five different vegetation mosaics in Ethiopia. The stem borer species diversity varied among vegetation mosaics and host plants. Forty‐four stem borer species belonging to 14 different genera in the families of Noctuidae, Crambidae, Pyralidae and Tortricidae were recorded from 34 wild host plants and through light trap. Among these families, Noctuidae was the highest in species richness in which 31 species were identified, out of which 15 species and two genera were new to science. This paper discusses the ecological interpretation of host plant–stem borer species interactions, particularly in relation to habitat disturbances.     

Multi-Season Regional Analysis of Multi-Species Occupancy: Implications for Bird Conservation in Agricultural Lands in East-Central Argentina

Rapid expansion and intensification of agriculture create challenges for the conservation of biodiversity and associated ecosystem services. In Argentina, the total row crop planted area has increased in recent decades with the expansion of soybean cultivation, homogenizing the landscape. In 2003 we started the first long-term, large-scale bird monitoring program in agroecosystems of central Argentina, in portions of the Pampas and Espinal ecoregions. Using data from this program, we evaluated the effect of land use and cover extent on birds between 2003-2012, accounting for imperfect detection probabilities using a Bayesian hierarchical, multi-species and multi-season occupancy model. We tested predictions that species diversity is positively related to habitat heterogeneity, which in intensified agroecosystems is thought to be mediated by food availability; thus the extent of land use and cover is predicted to affect foraging guilds differently. We also infer about ecosystem services provisioning and inform management recommendations for conservation of birds. Overall our results support the predictions. Although many species within each guild responded differently to land use and native forest cover, we identified generalities for most trophic guilds. For example, granivorous gleaners, ground insectivores and omnivores responded negatively to high proportions of soybean, while insectivore gleaners and aerial foragers seemed more tolerant. Habitat heterogeneity would likely benefit most species in an intensified agroecosystem, and can be achieved with a diversity of crops, pastures, and natural areas within the landscape. Although most studied species are insectivores, potentially beneficial for pest control, some guilds such as ground insectivores are poorly represented, suggesting that agricultural intensification reduces ecological functions, which may be recovered through management. Continuation of the bird monitoring program will allow us to continue to inform for conservation of birds in agroecosystems, identify research needed to reduce key uncertainties, and anticipate the effects of changes in agriculture in central Argentina.     

Insect declines and agroecosystems: does light pollution matter?

Drastic declines in insect populations, ‘Ecological Armageddon’, have recently gained increased attention in the scientific community, and are commonly considered to be the consequence of large‐scale factors such as land‐use changes, use of pesticides, climate change and habitat fragmentation. Artificial light at night (ALAN), a pervasive global change that strongly impacts insects, remains, however, infrequently recognised as a potential contributor to the observed declines. Here, we provide a summary of recent evidence of impacts of ALAN on insects and discuss how these impacts can drive declines in insect populations in light‐polluted areas. ALAN can increase overall environmental pressure on insect populations, and this is particularly important in agroecosystems where insect communities provide important ecosystem services (such as natural pest control, pollination, conservation of soil structure and fertility and nutrient cycling), and are already under considerable environmental pressure. We discuss how changes in insect populations driven by ALAN and ALAN itself may hinder these services to influence crop production and biodiversity in agricultural landscapes. Understanding the contribution of ALAN and other factors to the decline of insects is an important step towards mitigation and the recovery of the insect fauna in our landscapes. In future studies, the role of increased nocturnal illumination also needs to be examined as a possible causal factor of insect declines in the ongoing ‘Ecological Armageddon’, along with the more commonly examined factors. Given the large scale of agricultural land use and the potential of ALAN to indirectly and directly impact crop production and biodiversity, a better understanding of effects of ALAN in agroecosystems is urgently needed.     

Conservation biological control and enemy diversity on a landscape scale

Conservation biological control in agroecosystems requires a landscape management perspective, because most arthropod species experience their habitat at spatial scales beyond the plot level, and there is spillover of natural enemies across the crop–noncrop interface. The species pool in the surrounding landscape and the distance of crop from natural habitat are important for the conservation of enemy diversity and, in particular, the conservation of poorly-dispersing and specialized enemies. Hence, structurally complex landscapes with high habitat connectivity may enhance the probability of pest regulation. In contrast, generalist and highly vagile enemies may even profit from the high primary productivity of crops at a landscape scale and their abundance may partly compensate for losses in enemy diversity. Conservation biological control also needs a multitrophic perspective. For example, entomopathogenic fungi, plant pathogens and endophytes as well as below- and above-ground microorganisms are known to influence pest-enemy interactions in ways that vary across spatiotemporal scales. Enemy distribution in agricultural landscapes is determined by beta diversity among patches. The diversity needed for conservation biological control may occur where patch heterogeneity at larger spatial scales is high. However, enemy communities in managed systems are more similar across space and time than those in natural systems, emphasizing the importance of natural habitat for a spillover of diverse enemies. According to the insurance hypothesis, species richness can buffer against spatiotemporal disturbances, thereby insuring functioning in changing environments. Seemingly redundant enemy species may become important under global change. Complex landscapes characterized by highly connected crop–noncrop mosaics may be best for long-term conservation biological control and sustainable crop production, but experimental evidence for detailed recommendations to design the composition and configuration of agricultural landscapes that maintain a diversity of generalist and specialist natural enemies is still needed.     

Edges in Agricultural Landscapes: Species Interactions and Movement of Natural Enemies

Agricultural landscapes can be characterized as a mosaic of habitat patches interspersed with hostile matrix, or as a gradient of patches ranging from suitable to unsuitable for different species. Arthropods moving through these landscapes encounter a range of edges, with different permeability. Patches of native vegetation in these landscapes may support natural enemies of crop pests by providing alternate hosts for parasitic wasps and/or acting as a source for predatory insects. We test this by quantifying species interactions and measuring movement across different edge-types. A high diversity of parasitoid species used hosts in the native vegetation patches, however we recorded few instances of the same parasitoid species using hosts in both the native vegetation and the crop (canola). However, we did find overall greater densities of parasitoids moving from native vegetation into the crop. Of the parasitoid groups examined, parasitoids of aphids (Braconidae: Aphidiinae) frequently moved from native vegetation into canola. In contrast, parasitoids of caterpillars (Braconidae: Microgastrinae) moved commonly from cereal fields into canola. Late season samples showed both aphids and parasitoids moving frequently out of native vegetation, in contrast predators moved less commonly from native vegetation (across the whole season). The season-long net advantage or disadvantage of native vegetation for pest control services is therefore difficult to evaluate. It appears that the different edge-types alter movement patterns of natural enemies more so than herbivorous pest species, and this may impact pest control services.     

Composition of stem borer communities in selected vegetation mosaics in Kenya

Busseola fusca (Fuller), Sesamia calamistis Hampson, Chilo partellus (Swinhoe) and Chilo orichalcociliellus (Strand) are important stem borer pests of maize and sorghum in East Africa. Persistence of these pests in crop fields is blamed on the influx of diaspore populations from the neighbouring natural habitats. In addition to pest species, natural habitats support numerous non-economic stem borer species, some not known to science. However, due to growing human populations and accompanying global change, some of the natural habitats are undergoing rapid changes, a process that may result in the evolution of “new” pest species. In this study, we investigated stem borer species diversity in four different vegetation mosaics in Kenya, with an aim of establishing the differences in species composition and distributions in both wild and cultivated habitats. We identified 33 stem borer species belonging to 14 different genera in the four families; Noctuidae, Crambidae, Pyralidae and Tortricidae from 37 plant species. In addition to the above stem borer pest species, we found three more species, Busseola segeta Bowden, Pirateolea piscator Fletcher and Eldana saccharina Walker, in the cultivated fields. Together, stem borer pests varied in distribution among vegetation mosaics, suggesting differences in ecological requirement. Despite the variations in distribution patterns, stem borer pests co-existed with non-economic species in the natural habitats, communities that are facing threats due to ongoing habitat changes. This paper discusses the likely impacts of habitat changes on both pest and non-economic species.     

Relationships between biodiversity and biological control in agroecosystems: Current status and future challenges

Agricultural systems around the world are faced with the challenge of providing for the demands of a growing human population. To meet this demand, agricultural systems have intensified to produce more crops per unit area at the expense of greater inputs. Agricultural intensification, while yielding more crops, generally has detrimental impacts on biodiversity. However, intensified agricultural systems often have fewer pests than more “environmentally-friendly” systems, which is believed to be primarily due to extensive pesticide use on intensive farms. In turn, to be competitive, less-intensive agricultural systems must rely on biological control of pests. Biological pest control is a complex ecosystem service that is generally positively associated with biodiversity of natural enemy guilds. Yet, we still have a limited understanding of the relationships between biodiversity and biological control in agroecosystems, and the mechanisms underlying these relationships. Here, we review the effects of agricultural intensification on the diversity of natural enemy communities attacking arthropod pests and weeds. We next discuss how biodiversity of these communities impacts pest control, and the mechanisms underlying these effects. We focus in particular on novel conceptual issues such as relationships between richness, evenness, abundance, and pest control. Moreover, we discuss novel experimental approaches that can be used to explore the relationships between biodiversity and biological control in agroecosystems. In particular, we highlight new experimental frontiers regarding evenness, realistic manipulations of biodiversity, and functional and genetic diversity. Management shifts that aim to conserve diversity while suppressing both insect and weed pests will help growers to face future challenges. Moreover, a greater understanding of the interactions between diversity components, and the mechanisms underlying biodiversity effects, would improve efforts to strengthen biological control in agroecosystems.