The influence of pupal diapause on adult eclosion rhythm of Delia antiqua was investigated. When non-diapause and diapause pupae were exposed to various photoperiods at 15, 20 and 25 degrees C, both of them emerged as adults close to the light-on time, but the phase of eclosion varied with photoperiod and temperature. Moreover, there was a significant difference in the eclosion time between non-diapause and diapause pupae; the eclosion peak of diapause pupae was earlier than that of non-diapause pupae. When non-diapause and diapause pupae were transferred to constant darkness (DD) after having experienced LD 12:12 at 15, 20 and 25 degrees C, both showed circadian rhythmicity in eclosion. Although the free-running period (tau) decreased slightly as temperature increased in both non-diapause and diapause pupae, the latter tended to show shorter tau than the former. This observation suggests that the observed difference in eclosion time in LD cycles between non-diapause and diapause pupae is due to differences in tau.