Daily Time of Hatching in Nemobiine Crickets

Hatching rhythms were studied in 24-hour light-dark cycles in 6 species of nemobiine crickets, Pteronemobius ohmachii, P. nitidus, Dianemobius mikado, D. taprobanebsis, D. nigrofasciatus and D. fascipes. Four species of them prefer different habitat types in the temperate region but two species occur in the subtropical and tropical regions. Regardless of the difference in habitat climatic conditions, D. fascipes (tropical and subtropical) and D. nigrofasciatus (temperate) in the D. fascipes species complex hatch mainly during night, but the other four species showed a sharp peak around dawn under a photophase of 12 hours. The daily hatching rhythm became obscure under very long photophases of 20-21 hours in the 3 species examined, D. fascipes, D. taprobanensis and P. nitidus. The phase setting of the hatching rhythm depends on dusk in short photoperiods (≤6 h) and on dawn in long photoperiods (6-16 h) in D. fascipes and D. taprobanensis. Such a shift of time cue for hatching was not observed for P. nitidus whose time of hatching was equally influenced by dawn and dusk in either the short or long photoperiods.