Tachinids attack: Inferring the relative importance of host phylogeny and ecology on parasitism by the parasitoid flies (Tachinidae: Diptera)

Records of tritrophic interactions for the parasitoid family Tachinidae (Diptera) are sparse, preventing the investigation of how host ecology influences trophic interactions with this species rich group of natural enemies. Using global datasets of both herbivore-plant and tachinid-herbivore interactions, we estimated the relative importance of effects of herbivore diet (plant substrates) and evolutionary history (based on phylogeny) on parasitism by Tachinidae. A multivariate statistical method was used to project herbivores into niche-space, which quantified dissimilarity in host plant assemblages while controlling for geography. This metric was used to ask if herbivores are more likely to be attacked by a species of Tachinidae if they are (1) more similar in plant associations or (2) more phylogenetically related to a fly’s other known hosts. We found that the evolutionary history of an herbivore was a strong predictor of parasitism, and higher relatedness to other known hosts was a consistent predictor of attack across species of Tachinidae. Similarity in plant assemblage was equally strong, but not as consistent: for some species of Tachinidae similarity between host plant assemblages was a strong predictor of attack, while in others it played no role. In some notable instances, disparity between hosts plant assemblages increased the probability of attack. This was especially true for tachinid species where increased host relatedness seemed to play an important role in determining parasitism. This suggests that herbivore’s plant-ecology and evolutionary history determine their associations with Tachinidae, but the relative importance of these traits vary between species of Tachinidae.