Natural enemies and host breadth: A tritrophic analysis of diversification rates in Tortricidae (Lepidoptera)

Why are there so many species of plant-feeding insects? The most popular explanations focus on host-plant interactions. However, interactions with natural enemies could also be important. The tri-trophic niche concept, proposed by Singer and Stireman III (2005), predicts that diversification rates will be highest when there is strong pressure from specialized natural enemies, and high ecological opportunity. Here we test the predictions of the tri-trophic niche concept on the diversification of leafroller moths (Lepidoptera: Tortricidae) using a comparative phylogenetic approach. We use parasitoid assemblage richness as a proxy for specialized natural enemy pressure, and host plant range as a measure of ecological opportunity. We recover a positive relationship between natural enemy pressure and species richness. We also recover a positive relationship between natural enemy pressure and speciation rates, and a negative relationship between natural enemy pressure and extinction rates. Our results are consistent with the predictions of the tri-trophic niche concept, i.e., species richness and net diversification rates are positively correlated with natural enemy pressure. Natural enemy interactions should be considered more routinely in models of  plant-feeding insect evolution.