Rice stem borers (RSB) were studied near Yogyakarta, Indonesia, during the two rainy seasons of 1990-1991 and 1991-1992, and the dry season of 1991, when 4 different varieties of rice were tested for their natural resistance to RSB. We classified rice varieties by considering their susceptibility to pests, from Pelita, the most vulnerable rice variety, to Krureng Aceh, the most resistant, with IR64 and Cisedane falling somewhere in between. Three rice stem borers, which appeared in strict succession, were found. Scirpophaga (Tryporyza) incertulas, the most abundant of the three, generally attacked rice during the earliest and latest phases of their full cycle. The two others, Sesamia inferens and Chilo spp. preferred rice during its intermediate phases. Levels of damage appeared highly variable; the highest population levels of pests were observed during the rainy seasons, when damage to the plants often exceeded 10% of all rice stems (tillers), the accepted value in Indonesia for the RSB economic injury level. Natural enemies of RSB, comprised of many egg and larva parasites as well as many predators, barely controlled RSB during most of the plant cycle. Thus Bracon chinensis, although being the most numerous of all larva parasites, does not seem to be a key factor in control of RSB larvae populations.