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Title: Circadian rhythms in insects.
Author: Constantinou, C.
ISNI:       0000 0001 3561 4828
Awarding Body: Birkbeck (University of London)
Current Institution: Birkbeck (University of London)
Date of Award: 1979
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Patterns of locomotory activity were studied in adult triatomid bugs under various light-dark regimes by means of rocking acto graphs and suitable recording appartus. Under conditions of 12 hours of light, 12 hours of dark (LD 12:12) locomotor activity in Rhodnius prolixus, Triatoma infestans and Panstrongylus megistus was strictly nocturnal, with a pronounced peak occurring at the onset of darkness, In constant darkness (DD) and constant light (LL) the activity rhythm free-ran revealing its true circadian nature. In R. prolixus the period of the rhythm was shown to depend on the intensity of the light. When Rhodnius was exposed to LD cycles of various frequencies, the circadian rhythm became entrained only if the period of the LD regime lay between T = 18 and T = 32 hours. If the LD period was less than T = 18, the activity rhythm either free-ran (with an average period of about 27.5 hours) or attained a period of exactly 24 hours. When the change from light to darkness in LD 12:12 was advanced or delayed, Rhodnius re-entrained to the new LD regime, either immediately or after a few transient cycles, depending on the amount of phase change. Shifts in the phase of the freerunning rhythm were also produced by single pulses of light or darkness. The rhythm of Rhodnius also entrained after either the ocelli, the compound eyes or both had been occluded, indicating that extraocular photoreceptors may be involved. The pattern of oviposition in ~ prolixus, ~ megistus, T. infestans and T. phyllosoma shows a rhythm which is entrained by light-dark cycles with a 24-hour periodicity. In ~ megistus the circadian oviposition rhythm free-runs in DD. In LD cycles of T = 24 hours, a rhythm of ecdysis was observed whose timing was dependent on photoperiod. Ecdysis occurred before dawn when the photoperiod was short and after dawn when the days were long. Experiments indicated that, again, extraocular photoreceptors may be involved in entrainment. Continuous actograph records were obtained from individual desert scorpions Androctonous australis and Buthus occitanus and forest species Pandinus gregoryi and Hadogenese bicolour, under various lighting conditions. In LD 12:12 the desert scorpions were strongly nocturnal. Much of the activity of the forest species occurred in light. Detailed studies, however, revealed that these scorpions are nocturnal; the phase of their activity rhythm is set by the light-off signal. In both desert and forest species activity was circadian. In A. australis, activity could be entrained to LD 12:12 which was perceived by extraocular photorccptors in the mctasoma.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available