We sampled outbreak populations of western spruce budworm, Choristoneura occidentalis (Lepidoptera: Tortricidae), between 1997 and 2016 in Douglas-fir forests in the interior of British Columbia, Canada. Annual rates of change in population densities were correlated with generation survival, modulated by egg recruitment via dispersal of moths. Most temporal variation in generation survival was the result of variation in survival of small, non-feeding larval stages. Survival rates of feeding larval and pupal stages determined the magnitude of generation survival but contributed little to temporal trend. Survival of small larvae was the product of density-related losses of larvae dispersing to and from hibernation sites and weather-related stress caused by warm temperatures in late summer and early spring. Overwinter survival improved in cooler years and at higher elevations. Survival of feeding larvae and pupae was associated with mortality by natural enemies, in particular a few species of dominant, ubiquitous endoparasitoids, and an episodic, virulent baculovirus. Recruitment of eggs indicated emigration of gravid moths independent of defoliation but proportional to density of local moths. During periods of increasing and decreasing population densities over a large outbreak area, a marked differential in adult densities among locations resulted in greater than expected per-capita egg recruitment to areas of relatively low density and vice versa, indicative of net exchange of gravid moths from high- to low-density populations. The result was homogenization of egg densities among locations, apparent synchrony of the outbreak at the large scale, and extended duration of the outbreak at some locations, despite declining generation survival. These results are compared with field studies of the closely related spruce budworm, Choristoneura fumiferana. We suggest our interpretation applies more generally and outbreaks of conifer-feeding budworms are maintained for several years by compensatory survival of sequential life-history stages and spatio-temporal smoothing of densities via dispersal of gravid moths. Parasitoids and pathogens can cause sudden declines in densities, but populations inevitably wane as a result of cumulative degradation of their resource. The interaction and temporal sequence of bottom-up and top-down factors explain the similarities and differences in outbreak characteristics within- and among-budworm species.

中文翻译：

---

西部云杉蚜虫爆发种群的生态学

我们对西部云杉 budworm、Choristoneura occidentalis 的爆发种群进行了采样（鳞翅目： Tortricidae），1997 年至 2016 年间在加拿大不列颠哥伦比亚省内陆的花旗松森林中。种群密度的年变化率与世代存活率相关，通过飞蛾散布的卵子募集进行调节。世代存活率的大多数时间变化是小型非摄食幼虫阶段存活率变化的结果。摄食幼虫和蛹阶段的存活率决定了世代存活的大小，但对时间趋势的影响很小。小型幼虫的存活是由于幼虫分散到冬眠地点和从冬眠地点散布的密度相关损失以及夏末和早春温暖温度引起的与天气相关的压力的产物。在较冷的年份和较高的海拔地区，越冬存活率有所提高。摄食幼虫和蛹的存活与天敌的死亡率有关，特别是一些占优势的、普遍存在的内寄生物和一种偶发性、剧毒的杆状病毒。卵的募集表明妊娠蛾的迁徙与落叶无关，但与当地蛾的密度成正比。在大爆发区域的人口密度增加和减少期间，不同地点成虫密度的显着差异导致人均卵子募集到密度相对较低的地区大于预期，反之亦然，表明来自不同地区的孕蛾的净交换高密度到低密度的人群。其结果是各地鸡蛋密度均一，大规模爆发明显同步，部分地点爆发持续时间延长，尽管世代生存率下降。这些结果与密切相关的云杉芽虫的实地研究进行了比较，Choristoneura fumiferana。我们建议我们的解释更广泛地适用，并且通过连续生活史阶段的补偿存活和通过传播妊娠蛾的密度的时空平滑，将针叶树芽虫的爆发维持数年。寄生蜂和病原体会导致密度突然下降，但由于其资源的累积退化，种群不可避免地会减少。自下而上和自上而下因素的相互作用和时间顺序解释了芽虫物种内部和之间爆发特征的异同。