In the laboratory, larvae of the Western Palaearctic P. nymphula were exposed to conditions of temperature and food conducive to uninterrupted development, and to one of three, constant photoperiods; 13.5 h (equivalent to either equinox). 18 h (14 May and 30 July) and 19.5 h (5 June and 8 July), and their responses were interpreted in the light of seasonal development in the field. Synchronised entry to F-0 (the final instar) in late summer is caused by the summer arrest in F-l (the penultimate instar) that is induced by exposure in F-l, but not in F-2 or F-3, to 19.5 h, but not to 13.5 h. The refractoriness of F-l declines during summer so that the response to 19.5 h changes abruptly during late August (16-16.5 h; maximum daily increment of change of 5 min/day), when F-0 is entered promptly. Termination of emergence in summer is caused by the long-day arrest that prevents F-l larvae from entering F-0 during the second half of May (18 h or more). Photoperiod does not evidently affect the mean duration of F-2 or F-3, or the onset and rate of metamorphosis in spring. Persistent exposure to 19.5 h during their summer arrest causes about 25% of F-l larvae to undergo a supernumerary moult, still within F-l; such individuals can be distinguished from normal F-l (after the supernumerary moult) by their larger wing-sheaths; Supernumerary moulting occurs also in the field. Remaining unknown are; the responses of F-0 which prevent emergence (i.e. the onset of metamorphosis) in autumn; and the role, if any, of changing photoperiods in regulating rate of development or sensitivity to absolute photoperiod.


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Societas Internationalis Odonatologica

Philip S. Corbet, I.F. Harvey, J. Abisgold, & F. Morris. (1989). Seasonal regulation in Pyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae) 2. Effect of photoperiod on larval development in spring and summer. Odonatologica, 18(4), 333–348.