The ecology and evolution of tachinid-host associations

Abstract

The Tachinidae is a taxonomically and ecologically diverse clade of parasitoids for which evolutionary and ecological relationships with hosts are largely unknown. Here, I employed a multidisciplinary approach to evaluate the determinants of patterns of host use in the Tachinidae. First, I examined spatio-temporal variation in the tachinid-dominated parasitoid assemblage of one lepidopteran species Grammia geneura . The parasitoid assemblage and parasitism rates varied dramatically among and within sampling sites, seasons, and years. I show that this variability may be a function of habitat-specific parasitism and indirect interactions between this host and other Macrolepidoptera through shared tachinid parasitoids. I then experimentally examined the host selection process in the tachinid Exorista mella. Host movement was an important elicitor of attack behavior. Flies also responded to odors associated with food plants of their host. Experienced flies attacked hosts more readily than did inexperienced flies. Based on these results, I proposed a host selection scenario for this tachinid species. E. mella also teamed to associate colors with hosts and avoided deterrent models that they had experienced. However, I failed to find evidence for odor learning. Learning of host-associated cues by E. mella may allow this parasitoid to take advantage of abundant host populations and maintain host-searching efficiency in an unpredictable environment. To examine how host-associated characteristics evolved in the Tachinidae, I reconstructed the evolutionary relationships within the subfamily Exoristinae using molecular data. Phylogenetic analyses generally supported recent classifications. Analyses of host-related characters indicated that tachinids show great evolutionary lability in behavior, morphology, and host range. Finally, I sampled host species to assess the determinants of tachinid community structure and host range. Several host characteristics were found to affect tachinid species richness. These patterns may be due to the opportunistic use of abundant hosts by polyphagous tachinids, enemy-free space provided by well-defended hosts, and the process of host location. Patterns of tachinid host use varied significantly with sample size, host diet breadth, host gregariousness, plant form, and host morphology. Taken together, these studies indicate high levels of plasticity in tachinid-host associations. This may be responsible for their ecological and evolutionary success.