Abstract The effects of day length on adult diapause development, associated with diapause body colour change as well as postdiapause reproduction are studied in Nezara viridula from Japan. Facultative diapause spontaneously terminates under three constant short-day and near-critical photoperiods at 25 °C without low temperature treatment. The period required for body colour change from russet to green and the precopulation and preoviposition periods differ significantly between the photoperiodic treatments, being shortest under LD 13 : 11 h, intermediate under LD 12 : 12 h and longest under LD 10 : 14 h. Photoperiodic conditions do not affect postdiapause reproductive performance: the total egg production, duration of the period of oviposition and other reproductive indices do not differ significantly between the photoperiodic conditions. The total egg production depends on the duration of the period of oviposition but not on how long females remained russet during diapause. It is concluded that diapause in N. viridula does not require low temperature for its successful completion and diapause duration affects winter survival but not postdiapause reproductive performance or longevity. Such independence of the postdiapause reproductive performance from the duration of diapause may have contributed to the continuous worldwide range expansion of this species into temperate zone.