1. Observed lower levels of herbivory in mixed compared with monoculture stands have been hypothesized to depend on top‐down forces, through higher predation pressure by natural enemies or through bottom‐up mechanisms through plant quality effects on herbivore performance.
2. In this study, we compared the performance measured as host plant induced mortality, cocoon weight, and predation mortality of the European pine sawfly Neodiprion sertifer (Geoffroy) (Hymenoptera, Diprionidae) in mixed and monoculture forest stands.
3. We did not observe a difference in host plant induced mortality, cocoon weight, or predation mortality between mixed and monoculture forest stands. We did find an effect of local conditions around each experimental tree on pine sawfly performance. For example, the nitrogen content of pine needles is negatively affected by the proportion of pine around the experimental tree, which in turn increases the survival of sawfly larvae.
4. The results suggest that local conditions around individual trees are more important for the performance of the European pine sawfly than stand type, i.e. mixed or monoculture plant stands.
5. We conclude that the ongoing trend for diversification within commercial forestry calls for more research where the effects of both bottom‐up and top‐down effects are studied at several spatial scales.

中文翻译：

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林分类型对寄主植物品质的影响以及对松锯齿性能的直接和间接影响

1. 据推测，与单一栽培林相比，混合食草动物的食草水平较低，这取决于自上而下的作用力，天敌的更高捕食压力或自下而上的机制以及植物质量对食草动物性能的影响。
2. 在这项研究中，我们比较了混合和单一栽培林分中欧洲松树锯齿新di（Geoffroy）（膜翅目，双翅目）的寄主植物诱导的死亡率，茧重和捕食死亡率的表现。
3. 我们没有观察到混合和单一栽培林分之间寄主植物诱导的死亡率，茧重或捕食死亡率的差异。我们的确发现了每棵实验树周围的局部条件对松锯蝇性能的影响。例如，松针的氮含量受到实验树周围松树比例的负面影响，这反过来又增加了锯蝇幼虫的存活率。
4. 结果表明，相对于林分类型（即混合或单一种植的林分），单个树木周围的当地条件对于欧洲松锯齿的性能更为重要。
5. 我们得出的结论是，商业林业中的多样化趋势正在不断发展，需要进行更多的研究，其中要在几个空间尺度上研究自下而上和自上而下的效应。