Populations of the dark tussock moth,Dasychira basiflava(Packard), reached outbreak levels in eastern Connecticut between 1973 and 1975. Various stages of dark tussock moths were sampled between 1974 and 1975 from 5 sites to ascertain the natural enemies and their effects on the populations. The reason for the population collapse at 2 sites (Voluntown and Chaplin) is unknown. In Mansfield, a nuclear polyhedrosis virus (NPV) was important in causing the population collapse. The population collapse in Brooklyn was attributed in large part to larval parasitism and NPV and in Eastford primarily to larval parasitism.Eleven primary parasites, 3 hyperparasites, and 1 parasite of uncertain status were isolated in Connecticut. The total number of primary parasites now known to attack the dark tussock moth is 15. Seven pathogens were recovered of which the host specific NPV was the most prevalent.