Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Ecology. 2010 Nov;91(11):3284-93. doi: 10.1890/09-1314.1.
Phytophagous insects commonly interact through shared host plants. These interactions, however, do not occur in accordance with traditional paradigms of competition, and competition in phytophagous insects is still being defined. It remains unclear, for example, if particular guilds of insects are superior competitors or important players in structuring insect communities. Gall-forming insects are likely candidates for such superior competitors because of their ability to manipulate host plants, but their role as competitors is understudied. We investigate the effect of invasive populations of an oak gall wasp, Neuroterus saltatorius, on a native specialist butterfly, Erynnis propertius, as mediated by their shared host plant, Quercus garryana. This gall wasp occurs at high densities in its introduced range, where we stocked enclosures with caterpillars on trees that varied in gall wasp density. Biomass production of butterflies was lower in enclosures on high-density than on low-density trees because overwintering caterpillars were smaller, and fewer of them eclosed into adults the following spring. To see if the gall wasp induced changes in foliar quality, we measured host plant quality before and after gall induction on 30 trees each at two sites. We found a positive relationship between gall wasp density and the percentage change in foliar C:N, a negative relationship between gall wasp density and the percentage change in foliar water at one site, and no relationship between the percentage change in protein-binding capacity (i.e., phenolics) and gall-wasp density. Additionally, there was a negative relationship between foliar quality and butterfly performance. Our results provide evidence for a plant-mediated impact of an invasive oak gall wasp on a native butterfly and suggest that gall wasps could act as superior competitors, especially when they occur at high densities.
植食性昆虫通常通过共享的宿主植物相互作用。然而，这些相互作用并不符合传统的竞争范式，植食性昆虫的竞争仍在定义之中。例如，某些昆虫类群是否是优越的竞争者或在昆虫群落结构中扮演重要角色仍不清楚。瘿蜂是可能成为优越竞争者的候选者，因为它们能够操纵宿主植物，但它们作为竞争者的角色仍未得到充分研究。我们研究了入侵的栎瘿蜂种群（Neuroterus saltatorius）对其共同宿主植物鹅耳枥（Quercus garryana）上的本地专食性蝴蝶（Erynnis propertius）的影响，这种栎瘿蜂在其引入的范围内密度很高，我们在树上的封闭环境中饲养了毛毛虫，这些树的栎瘿蜂密度不同。由于越冬幼虫较小，并且次年春天更少的幼虫孵化成成虫，因此蝴蝶的生物量在高密度树上的封闭环境中比在低密度树上的要低。为了了解栎瘿蜂是否诱导了叶片质量的变化，我们在两个地点的 30 棵树上分别测量了诱导瘿瘤前后的宿主植物质量。我们发现，栎瘿蜂密度与叶片 C:N 百分比变化之间存在正相关关系，栎瘿蜂密度与叶片含水量百分比变化之间存在负相关关系，而蛋白质结合能力（即酚类物质）的百分比变化与栎瘿蜂密度之间没有关系。此外，叶片质量与蝴蝶表现之间存在负相关关系。我们的研究结果为入侵的栎瘿蜂对本地蝴蝶的植物介导影响提供了证据，并表明瘿蜂可能是优越的竞争者，尤其是当它们密度较高时。
