Population levels of Pseudoplusia includens (Walker) were found to vary considerably among agricultural ecosystems in Louisiana. The cotton, corn, and soybean ecosystem was characterized by a dense larval population in late August or September. Parasitism was inversely related to population density and to the amount of pesticides used in the surrounding area. Apanteles scitulus Riley and Copidosoma truncatellum (Dalman) were the predominant parasites, while Lespesia aletiae (Riley) was of lesser importance. The fungal pathogens Spicaria rileyi (Farlow) Charles and Massospora sp. attacked the soybean looper larvae at different periods and densities. S. rileyi appeared in midsummer at relatively low population densities, while Massospora sp. was present only in late August or September in very dense larval populations.