A fungal epizootic has been detected in populations of the scale Fiorinia externa Ferris (Hemiptera: Diaspididae) in the eastern hemlock, Tsuga canadensis (L.) Carriere (Pinales: Pinaceae), of several northeastern states. Colletotrichum acutatum Simmonds var. fioriniae Marcelino and Gouli var. nov. inedit (Phyllachorales: Phyllachoraceae), a well-known plant pathogen, was the most commonly recovered fungus from these infected scales. This is the second report of a Colletotrichum sp. infecting scale insects. In Brazil C. gloeosporioides f. sp. ortheziidae recovered from Orthezia praelonga is under development as a biopesticide for citrus production. C. acutatum was detected growing endophytically in 28 species of plants within the epizootic areas. DNA sequences of the High Mobility Box at the MAT1-2, mating type gene indicate that Colletotrichum sp. isolates recovered from scale insects and plants within epizootic areas were identical. Results from plant bioassays showed that this entomopathogenic Colletotrichum variety grew endophytically in all of the plants tested without causing external symptoms or signs of infection, with the exception of strawberry plants where mild symptoms of infection were observed. The implications of these findings with respect to the use of this fungus as a biological control agent are discussed.