The role of plant-associated microbes in regulating plant-herbivore interactions is an emerging research focus in plant science and community ecology. However, research in this area focused primarily on a few groups of plant-associated microbes such as mycorrhizae, plant-growth-promoting bacteria, and aerial obligate symbionts in grasses. The diverse endophytic fungi in roots receive far less attention and their importance in mediating plant defense, especially against root feeding insects, remains unclear. Our lab is investigating whether horizontally-transferred fungal endophytes can regulate plant defense against belowground herbivores. We are examining the effects of endophyte colonization on plant tissue chemistry as well as their influence on the production of volatile organic compounds in soils for plant indirect defense.