Data from: Patterns in parasitism frequency explained by diet and immunity

We sought to explain patterns in parasitism frequency of two specialist herbivores (Geometridae) by investigating the influence of plant diet as a source of variation in immune response variables important for defense against parasitism. Field collected caterpillars (Eois apyraria and Eois nympha) were assigned to one of two species in the plant genus Piper (Piperaceae): 1) a host species with high diversity of defensive chemistry, P. cenocladum C.DC., or 2) a host species with lower investment in chemical defense, P. imperiale C.DC. Hemolymph was extracted from fifth instar larvae, and immune strength measured unidimensionally using a phenoloxidase (PO) enzyme assay. Parasitism data came from 19 years of accumulated host plant-caterpillar-parasitoid associations from a long-term rearing project at La Selva Biological Station in Costa Rica, where the experiment took place. We found that immunity was significantly weakened when caterpillars were reared on the host plant with higher phytochemical diversity (P. cenocladum). Moreover, host plants inducing a weak immune response hosted caterpillars with higher parasitism rates. We conclude that patterns in parasitism frequency can be partially explained by cascading effects of host plant traits.

本研究旨在阐明两种专食性尺蛾科（Geometridae）植食昆虫的寄生频率模式，通过探究植物食性对免疫反应变量变异的影响——此类免疫反应变量是宿主抵御寄生的关键因子。研究人员将野外采集的尺蛾幼虫（Eois apyraria与Eois nympha）分别饲喂于胡椒属（Piper）的两种寄主植物（隶属于胡椒科Piperaceae）：其一为防御性化学成分多样性较高的P. cenocladum C.DC.，其二为化学防御投入较低的P. imperiale C.DC.。研究人员从5龄幼虫体内提取血淋巴，并采用酚氧化酶（phenoloxidase，PO）酶活性测定法对免疫强度进行单维度量化检测。寄生相关数据取自哥斯达黎加拉塞尔瓦生物站（La Selva Biological Station）长期饲养项目中积累的19年寄主植物-幼虫-寄生蜂关联记录，本实验即开展于该站点。研究发现，当幼虫饲喂于防御性化学成分多样性更高的寄主植物（P. cenocladum）时，其免疫能力显著减弱。此外，能诱导幼虫产生较弱免疫反应的寄主植物，其上的幼虫寄生率显著更高。本研究得出结论：寄主植物性状所产生的级联效应，可部分解释寄生频率的变化模式。