农业景观格局与麦蚜密度对其初寄生蜂与重寄生蜂种群及寄生率的影响

农业景观格局与过程能够强烈影响寄生蜂对寄主的寻找及寄生作用,寄主密度亦是影响寄生蜂分布的重要因素,然而农业景观的格局和寄主密度对寄生蜂寄生率的相互影响是一项值得研究的工作。在简单与复杂2种麦田农业景观结构下,调查了麦蚜的分布格局与2种寄主密度下麦蚜的初寄生率与重寄生率,分析了景观结构对麦蚜密度的影响、景观格局与麦蚜密度对寄生蜂寄生率与重寄生率的影响及交互作用。结果表明:景观结构的复杂性对麦蚜分布和寄生蜂初寄生率与重寄生率的影响均不明显,但寄主密度与景观结构的复杂性对寄生蜂的影响存在着明显的交互作用,寄主密度与寄生率呈正相关,寄主密度较低时烟蚜茧蜂为优势种,寄主密度较高时燕麦蚜茧蜂为优势种。麦蚜初寄生蜂与重寄生蜂对寄主密度的反应与其形态学、体型大小以及生活史特征相关,初寄生蜂与重寄生蜂的群落组成显著影响其对麦蚜的寄生率,而与景观结构的复杂性关系不大。

Effects of host density on parasitoids and hyper-parasitoids of cereal aphids in different agricultural landscapes

Several studies have shown positive responses of parasitism to either host density or landscape complexity. Many semi-natural arable habitats (Grasslands, woodlands, and wetlands) have been shaped by centuries of farming in China and worldwide. Established parasitoid populations have been recognized to provide pest management due to their high rates of consumption and precedence in wheat fields. However, no previous experiments have manipulated host density in agricultural landscapes of various complexity. Here we report the results of a field experiment conducted to determine how agricultural landscape complexity affects cereal aphids and how host density and agricultural landscape complexity jointly affect the parasitism, hyper-parasitism, and species diversity of parasitoids. Parasitism and hyper-parasitism were assessed by experimentally adding cereal aphids at low and high densities to commercial wheat fields located in two different agricultural landscapes in order to detect parasitism therein. Results showed that landscape complexity did not influence population density in cereal aphids. Landscape structure also did not influence parasitism and hyper-parasitism, contrary to our expectations. Increased host densities caused a trend of increasing abundance and species diversity in parasitoids and hyperparasitoids. Aphidius avenae Haliday parasitized a significantly greater proportion of hosts at low-host densities, while the opposite effect occurred for Aphidius gifuensis Ashmead. The discrepancy in responses of these parasitoids and hyper-parasitoids to host density is discussed in relation to differences in morphological traits, body size, and historical characteristics. The specific composition of parasitoid and hyper-parasitoid assemblage could significantly alter parasitism at various host densities at which landscape complexity and habitat composition impart negligible influence. Future studies should both evaluate plants with a more diverse range of traits and behaviors in landscapes with non-crop herbivore densities and span over more years to fully understand the impact of agricultural landscapes on species diversity and biological control service of parasitoids.