A large proportion of stem-boring larvae, attacking Italian ryegrass, were parasitized by hymenopterous parasitoids. The wingless braconid, Chasmodon apterus , was the most common parasitoid species. Chemical destruction of the old sward using the herbicide glyphosate prior to re-seeding did not significantly reduce the proportion of stem-boring larvae parasitized by C. apterus . Numbers of parasitized host larvae decreased more than the number of unparasitized larvae between 2 sampling dates.