温室白粉虱(Trialeurodes vaporariorum (Westwood))(同翅目:粉虱科)，是遍布于全世界的、十分常见的、高度多食性的有害昆虫。它对农业生产会造成极大的经济损失。尽管使用杀虫剂，但在许多温室生产中，温室白粉虱的危害仍然严重。拟寄生蜂一丽蚜小蜂 (Encasia formosaGahan)(膜翅目:蚜小蜂科)是温室白粉虱的一种自然天敌。如今，作为最有效的天敌昆虫，丽蚜小蜂已经在世界范围内被广泛地应用于控制温室作物上的温室白粉虱。 众所周知，在温室中引入了丽蚜小蜂后，温室白粉虱仍然能够以较低密度持续生存几个月(Burnett 1964,1967)。丽蚜小蜂对白粉虱的影响不仅会抑制白粉虱处于较低的密度，而且还会稳定白粉虱的种群。这是由于白粉虱对丽蚜小蜂的种群反应导致温室白粉虱的死亡产生的(Yano,1987)。因此研究温室白粉虱一丽蚜小蜂的种群动态是十分关键的。 在这篇论文中，详细介绍 了我们分别利用模型和实验两种方法对温室白粉虱一丽蚜小蜂系统所进行的研究工作。首先，为 了解种群动态复杂性产生的机制，我们建立了一个宿主一拟寄生蜂模型，模型包括温室白粉虱和它的寄生蜂丽蚜小蜂种群间的相互作用。由于，在一些实验中观察到，丽蚜小蜂寄生和取食温室白粉虱幼虫的两个反应都属于 Holling type II 功能反应(Arakawa,1981;Fransen,1987;Yano,1987)。所以，我们应用时间结构模型建立方程的时候，在其中加入Holling type II 功能反应。同时，在模型中，我们利用影响系数a和β对holling type II 功能反应进行修正，以体现在寄生蜂数目增多时，搜寻率的降低以及寄生和取食的比值的下降。 通过改变参数对这个宿主一拟寄生蜂模型进行模拟，我们得到如下重要结论:①丽蚜小蜂和温室白粉虱在初始时刻的数量比值对这种群动态会产生影响;②随着丽蚜小蜂密度的升高，丽蚜小蜂对温室白粉虱的捕食和寄生行为 产生的变化的强度对 于种群动态起了至关重要的作用;通过这个模型，我们再一次证实:外部环境条件不变时，自然种群会出现复杂性特征，如平衡态、周期振荡和混沌现象(不规则振荡)。 Roermund(1995)通过模型研究表明:当白粉虱的分布更加聚集时，拟寄生蜂受到的吸引越大，接 下来在已被白粉虱寄生的叶片上搜寻的强度越大，白粉虱种群被抑制的程度也就越强。受到这个模拟结果的启发，我们设计了一个实验，以便更进一步地了解影响丽蚜小蜂寄生白粉虱的空间动态的一些因素。更确切地说就是想要了解，在种群水平上，丽蚜小蜂寄生温室白粉虱幼虫的空间动态与温室白粉虱幼虫的密度大小或丽蚜小蜂的迁移距离是否有关。 通过对实验结果的统计分析，我们得出了如下结论:① 丽蚜小蜂寄生温室白粉虱幼虫的种群空间动态会受到两种因素的影响:距离因素和宿主幼虫的密度因素;② 距离因素的影响会随着丽蚜小蜂的扩散而消失;③ 宿主温室白粉虱幼虫的密度则一直会对 丽蚜小蜂的种群空间动态造成影响。

The greenhouse whitefly,Trialeurodes vaporariorum (Westwood),(Homoptera:Aleyrodiae),is a very common,highly polyphagous pest insect distributed all over the world.It can lead to serious economic losses in agriculture.Despite available insecticides,whiteflies are still a major economic problem in greenhouse crop production.The parasitoid Encasia formosa Gahan (Hymenoptera, Aphelinidae)is one of its natural enemies.Throughout world,as the validest enemy insect,E.formosa has been widely and successfully used for biological control of whiteflies on greenhouse crops. It is well known that the greenhouse whitefly population in a greenhouse persists for several months at low density when Encasia formosa is introduced (Burnett 1964,1967).The whitefly population is not only suppressed to low density but also is stabilized by E.formosa.These effects are caused by the mortality of whiteflies by which are the results of population responses of formosa (Yano,1987).So it is important to study the population dynamics of whitefly-E.formosa system. In this article,the study about whitefly-E.formosa system by modelling and experimentation is described in detail. In order to understand the mechanisms for generating dynamic complexity of the host-parastoid system,we formulated a pest-parasitiod model including interactions between greenhouse whitefly and its parastoid E.formosa population.Both responses of parasitization and host feeding by parasitoids to whitefly larvae showed a Holling type II responses in several experiments(Arakawa,1981;Fransen,1987;Yano,1987).So we formulated the temporally-structured model to simulate the population dynamics of whitefly-E.formosa system with Holling type II responses.Variations of Holling type II responses as modfied by the coefficient a and B so can show the decline of “the searching rate”and ratio of parasitization to host feeding in the attack by a parasitoid,with the increase of the number of parasitoid. By changing the coefficients,we simulate the population dynamics of whitefly-E.formosa system with the model.The main conclusions are:1.The rate of the number of whitefly to E.formosa at the initial phase,can influence the population dynamics;2.The behavioral changes in parasitization and host feeding when attacked by parasitiods,will appear with the increase of the number of parasites,the ranges of which are essentially important to influence the population dynamics;3.After model simulation,it will be verified that nature systems can generate complex behavior,e.g.,fixed points, periodic cycle and aperiodic oscillations in population abundance without any environmental change. According to modelling study,Roermund (1995)suggest that the stronger whitefly reduction when whiteflies are more aggregated is caused by a stronger parasitoid arrestment and sunsequent increase in the relative number parasitoids searching on infested leaflets.So we designed a experiment to understand the factors which affect the spatial dynamics of parasitization by E.formosa. That is to say,we want to estimate whether the spatial dynamics is related to the density of whiteflies or the distance between E.formosa and whitefly larva. According to statistics analysis,some conclusions can be made:①The spatial dynamics of parasitization by E.formosa is affected by two factors:distance and the density of whitefly larva;② Distance effect is diminished with the dispersal of E.formosa; The density of whitefly larva affect the spatial dynamics throughout the whole period.