Changes in thermal regimes that disparately affect hosts and parasitoids could release hosts from biological control. When multiple natural enemy species share a host, shifts in host-parasitoid dynamics could depend on whether natural enemies interact antagonistically versus synergistically. We investigated how biotic and abiotic factors influence the population ecology of larch casebearer (Coleophora laricella), a non-native pest, and two imported parasitoids, Agathis pumila and Chrysocharis laricinellae, by analyzing (i) temporal dynamics in defoliation from 1962-2018 and (ii) historical, branch-level data on densities of larch casebearer and parasitism rates by the two imported natural enemies from 1972-1995. Analyses of defoliation indicated that, prior to the introduction of parasitoids (1962 to ~1980), larch casebearer outbreaks occurred in 2 to 6 year cycles. This pattern was followed by a >15-year period during which populations were at low, apparently stable densities undetectable via aerial surveys, presumably under control from parasitoids. However, since the late 1990s and despite the persistence of both parasitoids, outbreaks exhibiting unstable dynamics have occurred. Analyses of branch-level data indicated that growth of casebearer populations, A. pumila populations, and within-casebearer densities of Ch. laricinellae - a generalist whose population dynamics are likely also influenced by use of alternative hosts - were inhibited by density-dependence, with high intraspecific densities in one year slowing growth into the next. Casebearer population growth was also inhibited by parasitism from A. pumila, but not Ch. laricinellae, and increased with warmer autumnal temperatures. Growth of A. pumila populations and within-casebearer densities of Ch. laricinellae increased with casebearer densities but decreased with warmer annual maximum temperatures. Moreover, parasitism by A. pumila was associated with increased growth of within-casebearer densities of Ch. laricinellae without adverse effects on its own demographics, indicating a synergistic interaction between these parasitoids. Our results indicate that warming can be associated with opposing effects between trophic levels, with deleterious effects of warming on one natural enemy species potentially being exacerbated by similar impacts on another. Coupling of such parasitoid responses with positive responses of hosts to warming might have contributed to the return of casebearer outbreaks to North America.

中文翻译：

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温暖的温度增加了非本地落叶者的种群增长并抑制了寄生蜂的人口反应

对寄主和寄生物有不同影响的热状态变化可能会使寄主脱离生物控制。当多个天敌物种共享一个宿主时，寄主-寄生物动力学的变化可能取决于天敌是对抗性相互作用还是协同性相互作用。我们通过分析 (i) 1962 年至 2018 年落叶的时间动态，研究了生物和非生物因素如何影响落叶松个案承载者 (Coleophora laricella)、一种非本地害虫和两种进口寄生蜂的种群生态学(ii) 1972-1995 年两种输入天敌的落叶松承载体密度和寄生率的历史、分支级数据。落叶分析表明，在引入寄生蜂之前（1962 年至 1980 年），落叶松病例爆发发生在 2 至 6 年的周期内。这种模式之后是一个 > 15 年的时期，在此期间，通过航空调查无法检测到人口处于低密度、明显稳定的密度，大概是受到寄生蜂的控制。然而，自 1990 年代后期以来，尽管两种寄生蜂持续存在，但仍发生了表现出不稳定动态的爆发。对分支级数据的分析表明，Ch. 的 casebearer 种群、A. pumila 种群和 casebearer 内密度的增长。laricinellae - 一种多面手，其种群动态可能也受到使用替代宿主的影响 - 受到密度依赖性的抑制，一年内的高种内密度会减缓下一年的增长。Casebearer 种群的增长也被 A. pumila 的寄生所抑制，但不受 Ch. 的抑制。落叶松属，并随着秋季气温升高而增加。A. pumila 种群的增长和 Ch。laricinellae 随着 casebearer 密度的增加而增加，但随着年最高温度的升高而减少。此外，A. pumila 的寄生与 Ch 的病例​​内密度的增加有关。laricinellae 对其自身的人口统计学没有不利影响，表明这些寄生蜂之间存在协同相互作用。我们的结果表明，变暖可能与营养水平之间的相反影响有关，变暖对一种天敌物种的有害影响可能会因对另一种天敌物种的类似影响而加剧。将这种寄生物反应与宿主对变暖的积极反应相结合，可能导致病例爆发回到北美。