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.本研究旨在阐释两种专食性植食性昆虫（尺蛾科，Geometridae）的寄生频率模式，通过探究植物食源作为抗寄生免疫反应变量变异的来源，这类免疫反应对抵御寄生至关重要。研究将野外采集的幼虫（Eois apyraria与Eois nympha）随机分配至胡椒属（Piper），隶属于胡椒科（Piperaceae）的两个寄主物种：1）防御性化学物质多样性较高的寄主物种P. cenocladum C.DC.；2）化学防御投入较低的寄主物种P. imperiale C.DC.。研究从5龄幼虫体内提取血淋巴（hemolymph），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检测。寄生相关数据来源于本实验开展地——哥斯达黎加拉塞尔瓦生物站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。研究发现，当幼虫取食植物化学多样性更高的寄主植物（P. cenocladum）时，其免疫能力显著减弱。此外，诱导幼虫产生较弱免疫反应的寄主植物，其上幼虫的寄生率更高。本研究得出结论：寄主植物性状的级联效应可部分解释寄生频率的变化模式。