The rice stink bug, Oebalus pugnax F., is of major economic importance to producers and millers of rice, Oryza sativa L. (Poaceae), because of the damaging effects of feeding during kernel development. Adult rice stink bugs cause yield loss and discoloration of rice kernels when feeding on panicles from anthesis to hard-dough stages of grain development, but damage by nymphs developing from the first to fifth instars has not been adequately studied. An experiment assessed the effect of rice stink bug nymphs on rice yield by caging egg masses on individual panicles and removing insects when adults emerged. A positive relationship between insect abundance and two measures of yield loss, unfilled kernels and milling loss, was very significant. Approximately 35% of eggs developed into fifth-instar nymphs in less than 21 days -- before kernels matured. Findings suggested that eggs and nymphs during early stages of rice panicle development should be considered in insecticidal treatment thresholds for rice stink bugs.