none Factors affecting parasitism of stem-boring larvae (especially Oscinella spp. and Geomyza tripunctata Fallen) which attack Italian ryegrass were studied. Stem-boring larvae dissected out of tillers from a range of Italian ryegrass cultivars showed parasitism of between 10-65%. However, the level of attack by Chasmodon apterus Nees, a ground-dwelling braconid which dominated the parasitoid complex, did not appear to be affected by the plant cultivar, independently of the level of stem-borer infestation. Italian ryegrass cultivars, newly-sown on land previously sown to barley and which had received conventional seed-bed cultivations, showed low levels of attack by C. apterus, but increased levels of attack by Halticoptera circulus Walker. The use of the pesticide phorate adversely affected parasitism by C. apterus.