During the 1991-92 season, a 1 ha block of unsprayed raingrown cotton near Dalby was sampled for parasite activity in heliothis larvae. As the parasites of interest mainly attack small larvae (see Murray and Rynne 1992), parasitism levels were determined by weekly collections of third and fourth instars. A single release of about 200 female Microplitis demolitor Wilkinson was made on 17 January 1992 to supplement natural parasite activity. In this paper we present data on larval parasitism and discuss possible interactions between parasites and a recently discovered pathogen