The beach ground cricket, Dianemobius csikii (Orthoptera: Trigonidiidae), collected from the mouth of the Kiyotake River, Miyazaki City, Miyazaki Prefecture, Japan (31.8°N, 131.5°E, 4.6 m elevation), is a bivoltine species and overwinters as the egg stage. This species has two wing forms, macropterous and brachypterous, and the macropterous rate at 28°C was higher in the long photoperiods. The effects of photoperiods on nymphal duration were small. The egg duration was affected by the rearing photoperiods of nymphs and adults and the egg-storing temperatures. The eggs were considered diapause eggs because when eggs were kept at 15°C for 20 weeks after oviposition, they were viable but did not hatch, regardless of the rearing photoperiods of nymphs and adults. At egg-storing temperatures of 20, 25, and 30°C, the egg duration showed two peaks, short and long, which were regarded as non-diapause and diapause eggs, respectively. The proportion of diapause eggs increased when the rearing photoperiods of nymphs and adults were short and eggstoring temperatures were low. When the rearing photoperiod of nymphs and adults was short, the diapause rate increased with increasing days after adult emergence. The egg diapause in D. csikii was determined by the rearing photoperiods experienced by nymphs and adults, egg-storing temperatures, and adult’s days after emergence. “Key words: adult’s days after emergence, egg diapause, egg-storing temperature, nymphal duration, nymph and adultrearing photoperiods, wing form”