Reversible reproductive diapause and intermediate states between diapause and full reproductive activity in male Oedipoda miniata grasshoppers

. Previous publications have shown that aestival reproductive diapause is reversible in Oedipoda miniata (Pall.) males. Short days and/or relatively low temperatures terminate diapause, whereas long days and/or high temperatures maintain or reinduce it. The previous studies proved, however, only the effect of the temperature, or of the daylength—temperature combinations, and employed only male mating behaviour as an indicator of the state of diapause. The present work demonstrates that diapause can be maintained, terminated, or reinduced, solely by changes in the daylength. At a constant 27°C, diapause was terminated under LD 10.5:13.5, whereas it was maintained or reinduced under LD 18:6. The reproductive accessory glands were small in diapausing males and large in post‐diapause ones, but their size decreased again with diapause reinduction, thus, they exhibited at least partially reversible changes. An intermediate state between full diapause and full reproductive activity was obtained under intermediate conditions of daylength and temperatures (LD 12:12; photophase (TP) at 38°C, scotophase (TS) at 27°C). In this state males showed consistently mild mating activity and intermediate size of the accessory glands, regardless of whether they had previously been in diapause or in post‐diapause states. Under another combination of intermediate conditions (LD 16:8; TP = 26°C, TS = 13°C), another intermediate state with consistently little mating activity was observed. The ‘all or none’ principle does not apply to this diapause, rather the state of diapause may take any stable intermediate level between full diapause and full reproductive activity. The physiological and ecological implications of these findings are discussed.