Klemola Tero, Andersson Tommi, Ruohomäki Kai
Section of Ecology, Department of Biology, University of Turku, 20014, Turku, Finland,
Oecologia. 2014 Aug;175(4):1211-25. doi: 10.1007/s00442-014-2984-9. Epub 2014 Jun 24.
Many populations of forest Lepidoptera exhibit 10-year cycles in densities, with impressive outbreaks across large regions. Delayed density-dependent interactions with natural enemies are recognized as key factors driving these cyclic population dynamics, but emphasis has typically been on the larval stages. Eggs, pupae and adults also suffer mortality from predators, parasitoids and pathogens, but little is known about possible density relationships between mortality factors and these non-feeding life stages. In a long-term field study, we experimentally deployed autumnal moth (Epirrita autumnata) eggs and pupae to their natural enemies yearly throughout the 10-year population cycle in northern Norway. The abundance of another geometrid, the winter moth (Operophtera brumata), increased in the study area, permitting comparisons between the two moth species in predation and parasitism. Survival of autumnal moth eggs and pupae was related to the moth abundance in an inverse and delayed manner. Egg and pupal parasitoids dominated as density-dependent mortality factors and predicted the subsequent growth rate of the host population size. In contrast, effects of egg and pupal predators were weakly density dependent, and generally predation remained low. Parasitism rates did not differ between the autumnal and winter moth pupae, whereas predators preferred winter moth pupae over those of the autumnal moth. We conclude that parasitism of the autumnal moth by egg and pupal parasitoids can be related to the changes of the moth density in a delayed density-dependent manner. Furthermore, egg and pupal parasitoids cannot be overlooked as causal factors for the population cycles of forest Lepidoptera in general.
许多森林鳞翅目昆虫种群的密度呈现出10年的周期，在大片区域会出现令人瞩目的爆发式增长。与天敌之间延迟的密度依赖相互作用被认为是驱动这些周期性种群动态的关键因素，但通常重点都放在幼虫阶段。卵、蛹和成虫也会遭受捕食者、寄生蜂和病原体造成的死亡，但对于死亡因素与这些非取食生命阶段之间可能的密度关系却知之甚少。在一项长期的野外研究中，我们在挪威北部10年的种群周期内，每年都将秋尺蠖（Epirrita autumnata）的卵和蛹实验性地投放给它们的天敌。研究区域内另一种尺蛾——冬尺蠖（Operophtera brumata）的数量增加了，这使得我们能够比较这两种尺蛾在被捕食和被寄生方面的情况。秋尺蠖卵和蛹的存活率与尺蛾数量呈反比且存在延迟关系。卵和蛹的寄生蜂作为密度依赖的死亡因素占主导地位，并预测了宿主种群数量随后的增长率。相比之下，卵和蛹捕食者的影响对密度的依赖性较弱，而且总体捕食率仍然较低。秋尺蠖和冬尺蠖蛹的被寄生率没有差异，而捕食者更喜欢捕食冬尺蠖的蛹而非秋尺蠖的蛹。我们得出结论，卵和蛹的寄生蜂对秋尺蠖的寄生可能以延迟的密度依赖方式与尺蛾密度的变化相关。此外，一般而言，卵和蛹的寄生蜂作为森林鳞翅目昆虫种群周期的因果因素不能被忽视。
