Photoperiodic stimuli which induce and terminate nymphal diapause in the small brown planthopper, Laodelphax striatellus, were examined with the nine local populations in Japan to identify geographic differences in their diapause pattern. The nymphal diapause was induced by short-day photoperiod. The population from Kamikawa, the northern region, diapaused even under 14L-10D photoperiod, while the population from the southernmost region, Ishigaki, did not diapause. There was a geographic cline in critical photoperiod for diapause; the populations from the higher latitude had longer critical daylength. The diapausing nymphs became adults in a certain period of time after being transferred to a long-day photoperiod. The period for the Kamikawa population, however, was longer than that for the other populations. This difference was caused mainly by retardation of the first moult after diapause in the Kamikawa population. The geographic differences in diapause termination were also observed among the local populations. The absolute photoperiod was unlikely to be an important factor for the diapause termination, while extension of daylength appeared to act as a terminating stimulus.