Chilling induces prompt and synchronised hatching after obligatory diapause in the subtropical cricket Cardiodactylus guttulus

Cardiodactylus guttulus is a subtropical cricket endemic to the Ryukyu Islands. C. guttulus has a univoltine life cycle with an obligatory diapause in embryos during winter. An environmental time cue(s) is required to terminate diapause and synchronise the life cycle with the seasonal cycle. In several temperate crickets, chilling terminates embryonic diapause and induces prompt and synchronised hatching. In the present study, by observing the day of hatching after chilling, we investigated whether C. guttulus terminates embryonic diapause with reference to temperature as shown in temperate crickets. After chilling at 16°C, the hatching rates to day 120 after oviposition increased compared to the control maintained at 25°C without chilling. When the chilling treatment lasted more than 30 days, hatching occurred synchronously, showing that chilling at 16°C for 1 month is sufficient to terminate diapause and induce synchronised hatching in C. guttulus. In addition, longer exposure to 16°C was associated with shorter days of transfer from 16 to 25°C to hatching. This result suggests that embryogenesis post-diapause progressed slowly during chilling. These characteristics would be adaptive to warm winters in subtropical regions.