Department of Biology, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland.
J Anim Ecol. 2011 Nov;80(6):1324-9. doi: 10.1111/j.1365-2656.2011.01866.x. Epub 2011 May 25.
1. Natural enemies may direct the host use of herbivorous insects on those hosts that ensure highest survival, thus creating enemy-free space. Host structure may contribute to enemy-free space if the current host ensures better refuge from natural enemies than other potential hosts. So far, however, direct evidence of the role of host structure for enemy-free space is lacking. 2. This study looks at the effect of physical host structure on the previously demonstrated enemy-free space of a lichen-feeding moth, Cleorodes lichenaria by manipulating the structure of host lichens and the access of natural enemies to larvae in the field. It was predicted that if larvae receive enemy-free space on Ramalina lichens because of their shrubby appearance, larvae should survive better on shrubby than on flat lichens in the presence of natural enemies but not in the absence of natural enemies. 3. Larvae survived better on shrubby than flat lichens and when the access of natural enemies to larvae was prevented than in the presence of them. According to the prediction, larvae in the presence of natural enemies survived better on shrubby compared with flat thalli but not in the absence of natural enemies. Thus, shrubby host structure promotes survival of larvae and underlies the enemy-free space on Ramalina species in natural conditions. 4. Host structure as a mechanism for enemy-free space and the direct impact of host structure for the performance of C. lichenaria larvae are discussed. Other potential reasons, such as lichen secondary chemicals and host-induced colouration of larvae as a basis of enemy-free space, are also discussed.
自然天敌可能会引导草食性昆虫选择那些能够确保最高存活率的宿主，从而创造出无天敌的空间。如果当前的宿主比其他潜在的宿主能更好地躲避天敌，那么宿主结构可能有助于创造无天敌的空间。然而，到目前为止，还缺乏宿主结构对无天敌空间作用的直接证据。
本研究通过在野外操纵宿主地衣的结构和天敌接触幼虫的方式，考察了宿主物理结构对先前证明的食藓蛾Cleorodes lichenaria 无天敌空间的影响。预测如果幼虫因为其灌木状的外观而在地衣 Ramalina 上获得无天敌的空间，那么在有天敌存在的情况下，幼虫在灌木状地衣上的存活率应该比在平坦地衣上更高，但在没有天敌的情况下则不然。
幼虫在灌木状地衣上的存活率高于平坦地衣，而且当阻止天敌接触幼虫时，其存活率高于有天敌存在的情况。根据预测，有天敌存在时，幼虫在灌木状地衣上的存活率高于平坦地衣，但在没有天敌的情况下则不然。因此，灌木状的宿主结构促进了幼虫的存活，并为 Ramalina 物种在自然条件下的无天敌空间提供了基础。
讨论了作为无天敌空间机制的宿主结构以及宿主结构对 C. lichenaria 幼虫表现的直接影响。还讨论了其他潜在的原因，例如地衣次生化学物质和幼虫作为无天敌空间基础的宿主诱导变色。
