In the current need of optimizing agricultural production, endophytic fungi are increasingly seen as part of the solution. Trichoderma, subject of this review, colonizes the most external layers of the root, improving plant growth. This colonization also induces plant defenses, helping the plant to minimize pest damage. However, if the fungi enter vascular tissues, necrosis and nutrient competition occurs. Easily dispersed in the environment, the fungi may affect other targets, such as insects, if the spores manage to penetrate the insect cuticle. Mostly seen as a race for resources, space, and with a possible interplay of toxins, Trichoderma may act as a powerful bioinsecticide. Unforeseen effects on other organisms of the ecosystem and trophic chain that might get exposed are also reviewed.
