多空间尺度下农田景观格局对玉米田天敌瓢虫种群动态影响机制的研究

Agricultural intensification has significantly altered the landscape patterns, and this will inevitably affect the population dynamics of natural enemy in agricultural ecosystem. Our present project will assess the effects of agricultural landscape pattern changes on predatory ladybeetles, Propylaea japonica and Harmonia axyridis, and their prey, Rhopalosiphum maidis in maize fields in North China. Agricultural landscape characteristics were obtained by using satellite remote sensing image and land cover classification. Predatory ladybeetles and R. maidis densities were monitored by using direct observation and yellow sticky cards together. The temporal and spatial distribution of predatory ladybeetles and R. maidis were analyzed by using spatial statistics related methods. DNA barcode technology was adopted to build trophic links between predatory ladybeetles and R. maidis in different landscapes. The relationships among the composition, configuration and complexity of landscape and abundance of predatory ladybeetles and R. maidis, and predation frequency on R. maidis were analyzed by using partial least squares regression (PLS). The goal of this project is to study the temporal and spatial distribution, population dynamics, and the biological control services of natural enemies in regional agricultural landscape at multiple spatial scales. All these findings will clearly reveal the mechanism that agricultural landscape pattern changes drive the population dynamics of natural enemy. Additionally, this is also the basis of ecological control of maize insect pests by using habitat management in practice.

农业生产的集约化导致农田景观发生了显著的变化，这种变化势必影响到农田生态系统中自然天敌种群的动态过程。本项目拟以我国华北农田景观格局变化为作用因素，以玉米田的捕食性天敌（龟纹瓢虫和异色瓢虫）及其猎物（玉米蚜）为研究对象，基于卫星遥感影像和土地覆盖分类，解析农田景观格局特征，结合田间调查数据，采用空间统计学方法研究异质性的景观中天敌瓢虫种群和猎物种群的时空分布特征及二者的空间关系；基于DNA分子标记技术，定量评价不同景观中两种捕食瓢虫对玉米蚜的捕食频率；应用偏最小二乘回归法（PLS）分析农田尺度和景观尺度下农田景观的组成、结构和多样性与天敌瓢虫和猎物种群数量及捕食频率的关系。阐明区域性农田景观中玉米田天敌瓢虫的时空分布特征、种群变化规律及控害作用。由此，理论上揭示农田景观格局变化驱动天敌瓢虫种群数量变化的机制，实践上为基于生境管理强化天敌控制玉米害虫种群提供新的思路和方法。

农田景观变化势必影响到生活在其中的害虫和天敌种群。本项目以农田景观格局变化为作用因素，以玉米田主要害虫和天敌瓢虫为研究对象，研究了多空间尺度下昆虫分布和农田景观因子对昆虫种群的驱动效应。结果表明玉米蚜、玉米螟、桃蛀螟、龟纹瓢虫、异色瓢虫种群均呈空间聚集分布，两种瓢虫之间的空间分布正相关，且均与玉米蚜正相关，玉米螟和桃蛀螟则呈现空间上的负相关。相比种间作用，不同尺度下景观因子对蚜虫和瓢虫种群的影响较小，瓢虫种群数量均与蚜虫种群正相关。1km下草地面积比例显著负影响龟纹瓢虫种群，而2.0、2.5和3.0km下水体面积比例显著正影响异色瓢虫，异色瓢虫也受到2.5km和3.0km尺度下玉米面积比例的负影响。玉米螟种群密度与玉米种植面积比例显著正相关，但是桃蛀螟则与玉米种植面积呈负相关。当玉米种植面积比例小于31%时，玉米螟种群低于经济阈值；但当玉米种植面积比例大于27%或23%时，桃蛀螟种群数量低于经济阈值。玉米面积是玉米螟种群数量的主要决定因素，而桃蛀螟种群则受益于非作物生境中的其他资源。H2、H12和H23是玉米螟线粒体DNA中主要的单倍型，其他类型发生频率非常低。155个单倍型可以分成三个类别Cluster 1~3，其中H12与玉米面积比例显著正相关，而与其他非玉米作物面积负相关。Cluster 2的主要单倍型为H23，该类与半自然生境显著负相关，Cluster 3没有占据优势的单倍型，也没有受到景观因子的影响。H12可能是与玉米种植面积有关的单倍型。总之，玉米田主要害虫和天敌瓢虫呈现聚集性空间分布及紧密的空间关系，种间作用显著影响蚜虫和瓢虫的种群密度，农田景观单一化导致不同食性害虫的反应不一致，并显著影响到害虫的种群遗传结构。这些结果丰富了农田景观-害虫-天敌互作的理论，也为通过优化景观控制害虫奠定了基础。