What do we call fungi that grow inside grass plants and help them tolerate insect feeding?

Endophytic fungi are specialized organisms that reside within the tissues of plants, including grasses, without causing apparent harm. Their presence enhances the plant's health and resilience, particularly in dealing with external stressors such as insect feeding. These fungi often produce compounds that deter herbivores and strengthen the plant's ability to withstand various forms of stress, including drought and disease.

In contrast, pathogenic fungi are those that cause diseases in plants. Mycorrhizal fungi, while beneficial and associated with roots to enhance nutrient uptake, do not specifically help grasses tolerate insect feeding. Symbiotic fungi can be a broader category that includes various relationships but does not specifically describe the inward growth and protective role of endophytic fungi in grass plants. Therefore, endophytic fungi are the correct answer as they uniquely contribute to a grass plant's resilience to insect feeding.