Mycorrhizal mediation of insect herbivory and plant reproduction on Nicotiana species in the greenhouse

Arbuscular mycorrhizal (AM) fungi associate with many different plants and affect them in several ways. Besides contributing positively to plant growth, AM fungi benefit plants by increasing plant resistance to herbivory. AM fungi may affect how herbivore natural enemies find or parasitize their hosts. In many cases AM fungi are mutualists, increasing plant fitness, but they also can function parasitically, reducing plant fitness.; Mycorrhizal fungi affect plant physiology and thus, insect herbivores. However, it is not well understood how AM fungi effect herbivores or herbivore natural enemies. Most studies of AM fungi focus on plant growth effects, but there are other effects of AM fungal species not measured by plant growth. For example, different isolates of AM fungi probably do not affect plant growth differently, but it is unknown how different isolates of fungi (local or non-local) affect insect herbivores.; Because of these gaps in the literature, I decided to test several hypotheses of mycorrhizal-plant-herbivore-natural enemy interactions using Nicotiana rustica and N. tabacum. First, it was hypothesized that AM colonized plants would have reduced mirid populations. Second, AM colonized plants would have reduced whitefly populations. Third, whitefly parasitism would be higher on AM plants than non-AM plants. Fourth, that herbivore populations would be lower on plants colonized by a Glomus etunicatum isolate from Georgia, where tobacco is found, compared to an Arizona isolate, where tobacco is not found. Finally, I hypothesized that plant fitness would not differ between G. etunicatum isolates.; Mycorrhizal colonization generally negatively affected mirids but did not affect whitefly populations. Percent parasitism was higher on AM fungal colonized plants, meaning that AM effect how parasites either host find or parasitize. Mycorrhizal plants growing in pots in the greenhouse had much reduced fitness (∼4–5 times) compared to non-mycorrhizal control plants. Biologically, this implies that AM colonized plants germinating late in the season would likely have reduced fitness.; These experiments confirm that AM fungi affect some insect herbivores and can affect higher trophic-level interactions. Additionally, they demonstrate that the role of AM fungal colonization is much broader than just effects on plant growth or plant communities.