IRRI is developing rice varieties with higher yield potential by changing rice architecture to match an ideotype known as the new plant type (NPT) (Peng et al 1994). The features of the NPT include fewer and larger tillers, all of which are productive; sturdy stems; and erect, deep green leaves. At the IRRI Experiment Station, some plots of NPT lines have been highly damaged by stem borers, particularly by striped stem borer (SSB) Chilo suppressalis (Walker). We conducted a field screening of NPT lines and existing IRRI varieties to compare levels of stem borer damage. We also examined the relation of tiller number and silica content to stem borer damage.