title: Photoperiodism of diapause induction in Thyrassia penangae (Lepidoptera: Zygaenidae).
abstract: Thyrassia penangae enters winter diapause as a prepupa in a cocoon. Photoperiodism of diapause induction was systematically investigated in this moth. The photoperiodic response curves under 24-h light-dark cycles showed that this insect is a typical long-day species. The critical daylength was 13h 30min at 25 degrees C, 13h at 30 degrees C and 12h 20min at 28 degrees C. Transferring experiments from a short day (LD 12:12) to a long day (LD 15:9) or vice versa indicated that photoperiodic sensitivity mainly occurs during the larval period. In experiments using non-24-h light-dark cycles, when the length of photophase exceeded the critical daylength (13.5h), was diapause inhibited effectively, even when the length of scotophase exceeded the critical nightlength (10.5h). Only when a long scotophase was combined with a short photophase, diapause was induced effectively. This result suggests that daylength measurement is more important than nightlength measurement in T. penangae. Night interruption experiments under 24-h light-dark cycles exhibited two points of apparent light sensitivity, but the photosensitive position was highly influenced by temperature and the length of scotophase. Nanda-Hamner experiments failed to reveal the involvement of a circadian system in this photoperiodic time measurement. All light-dark cycles from LD 12:12 to LD 12:72 resulted in a short day response, and all cycles from LD 14:4 to LD 14:72 resulted in a long day response, suggesting that photoperiodic time measurement in this moth is performed by a day-interval timer or an hourglass-like clock.
authors.affiliation: Institute of Entomology, Jiangxi Agricultural University, Nanchang, China.
authors.forename: Hai-Min
authors.initials: HM
authors.lastname: He
authors.forename: Zhen-Hua
authors.initials: ZH
authors.lastname: Xian
authors.forename: Fang
authors.initials: F
authors.lastname: Huang
authors.forename: Xing-Ping
authors.initials: XP
authors.lastname: Liu
authors.forename: Fang-Sen
authors.initials: FS
authors.lastname: Xue
mesh_terms: D000818:Animals; D007814:Larva / Q000254:growth & development / Q000528:radiation effects; D008027:Light; D008675:Metamorphosis, Biological / Q000528:radiation effects*; D009036:Moths / Q000254:growth & development* / Q000528:radiation effects*; D017440:Photoperiod