The extraordinary diversity of tropical herbivores may be linked to hostplant specialization driven in part by variation in pressure from natural enemies. We quantified levels of host-specificity and parasitoid attack for the specialist herbivore, Eois (Geometridae). The goals of this research were to examine: 1) whether Eois are specialized on the genus Piper (Piperaceae) and if hostplant specialization varies geographically; 2) whether Eois are equally vulnerable to parasitoid attack across different geographic regions and by the same parasitoid families; and 3) whether parasitism levels vary with precipitation and elevation. Based on over 15,000 rearings, we found Eois caterpillars feeding exclusively on Piper. However, we did not detect geographic differences in host-specificity; each Eois species fed on an average of two Piper species. Parasitism levels of Eois varied significantly with climate and topography; Eois were most vulnerable to parasitoid attack in moist versus dry and wet forests and at low versus high elevations. The diversity of parasitoid families reared from Eois was greater in Ecuador and Costa Rica than in Panama, where parasitoids were primarily in the family Braconidae. The quantitative evidence for host-specificity provides support for the hypothesis that Eois are specialized on Piper. Our results also reveal that Eois are exposed to a mosaic of potential selective pressures due to variation in parasitoid attack over a large spatial scale.