Fungal endophytes have been found in leaves of all trees examined thus far -- from mangroves to rainforests to dry deserts, coastal salt marshes, and forests in boreal latitudes. Foliar endophytes accumulate by contagious spread -- and individual leaves may have dozens of species within their asymptomatic tissues. The consequences of these numerous and diverse infections for leaf nutrient status, palatability to folivores, developmental patterns, longevity, and rate and quality of decay are not known. The Arnold lab is examining the ecological and biochemical effects of endophyte infections in foliage of temperate and tropical plants, providing a background for related studies regarding the behavior and foraging patterns of folivorous insects, nutrient cycling in natural and altered ecosystems, and potential applications in biological control.