none A field study was carried out in Lapa, Parana, from June to October, 1977, to investigate the occurrence of lepidopterous larvae and their natural enemies on a barley crop. Plant examination, water traps, and pitfall traps were used to estimate the populations. A single species was found feeding voraciously on leaves and ears of barley plants, Pseudaletia sequax Franclemont, 1951. These larvae were more abundant between the end of August and Mid-September, during heading. The number of larvae found on plants was low; on the other hand, the capture in the pitfall was higher. Larval mortality was mainly due to the nuclear polyhedrosis virus (3.19%), which occurred between the end of August and Mid-October. The parasitoid Apanteles muesebecki Blanchard, 1947 (Hymenoptera, Braconidae) killed 10.6% of the larvae, at the same period of the virus infection.