Mycorrhiza-induced trophic cascade enhances fitness and population growth of an acarine predator.

Research on trophic cascades in terrestrial ecosystems has only recently revealed that root-associated organisms interact with organisms living on aboveground plant parts. Arbuscular mycorrhizal (AM) symbiosis is a ubiquitous phenomenon, yet studies on its effect on aboveground natural enemies of herbivores are scarce and mainly deal with plant-mediated rather than herbivore-mediated interactions. Here, we studied herbivore-mediated effects of AM symbiosis on an acarine predator. We measured life history characteristics and population growth rates of Phytoseiulus persimilis preying on two-spotted spider mites, Tetranychus urticae, which were feeding on bean plants colonized or not colonized by the AM fungus Glomus mosseae. All major life history characteristics of P. persimilis, foremost oviposition rate, minimum prey requirements needed to reach adulthood, and developmental time, were positively affected by AM colonization of the host plant of their prey, together resulting in enhanced population growth rates of the predators. Hence, we hypothesize that a bottom-up trophic cascade may counteract the apparent negative effects of mycorrhizal symbiosis when promoting herbivory by promoting the predation of herbivores due to improved prey quality. We argue that this pathway may be involved in stabilizing plant-mycorrhizal symbiosis in ecosystems over time.