University of Nevada, Reno RENO, Nevada, United States
Abstract: Insects have surpassed all other terrestrial animals in diversity due, in part, to their intense partitioning of resources. For herbivorous insects the primary resources are larval host plants, and for parasitoids they are other insects. For this reason, parasitoids are an exemplary system for studying dietary specialization across trophic-levels, as determinants of herbivore diet-breadth may enhance or inhibit their suitability as hosts for the higher trophic level. Despite this, many groups of parasitoids are understudied, and comprehensive records of host-parasite associations have seldom been compiled. In particular, we do not know if factors that structure diet breadth and host assemblages for herbivores will have similar importance for parasitoids. Historical metrics of trophic specialization include phylogenetic distance between hosts, the total number of hosts, types of host defenses, and other axes of life-history variation. An alternative to these diet-breadth metrics (proposed by Fordyce et al. 2016) is to characterize the landscape of host associations from the perspective of known plant-insect (or insect-parasitoid) interactions, thus capturing properties of hosts that are relevant to the herbivores (or parasitoids) but that are not directly quantified. In this study, (1) this model of dietary specialization is contrasted with historically-preferred metrics and (2) is used to construct models for predicting dietary specialization and host assemblages at a third trophic level. Among other results, we find that covariance between parasitoid and host diet breadth suggests caterpillars with variable host-plant use harbor more species of tachinid-fly, while dietary-specialists harbor fewer. Additionally, pairwise assessment of tachinidae indicates short term phylogenetic-conservatism of host-use, with many genera within Tachinidae preferring one or two families of host-species.
