Estimated levels of larval parasitism of the armyworm Mythimna separata (Walker) before and after the introduction of the parasitoid Apanteles ruficrus (Haliday) from Pakistan suggest that there has been an increase in average parasitism from c. 50-55% to c. 80%. Larval parasitism is not density dependent. M. separata pupal parasitism is density dependent. A. ruficrus parasitism reduces M. separata larval food consumption. The increased parasitism following the introduction of A. ruficrus is judged to have raised the armyworm population damage threshold in maize from c. 240-360 larvae m super(-2) to 400-530 larvae m super(-2). none