Pupal diapause in the eastern tiger swallowtail. Prrpilio glaucus L., is obligatory or facultative depending on subspecies. The southern subspecies, P.g.glaucus has a facultative diapause, induced by a larval exposure to short photoperiods. In the northern subspecies. P.g. canadensis, diapause is obligatory, occurring in each generation. F, hybrids inherit the diapause response of their father or respond differently from either parent. The incidence of diapause in hybrids was associated with sex, indicating that the diapause response may be determined by a n X-linked gene.

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Progeny of Sarcophaga bullata produced from mothers with a history of short day will not enter pupal diapause even if they are reared in a strong diapause-inducing environment (LD 12:12 h at 20°C). Short-day exposure and diapause commitment are normally inseparable, but this maternal effect provides a tool for examining separately the effect of photoperiod and diapause commitment. Duration of the wandering period of the third instar is longer in diapause-destined larvae than in non-diapause-destined larvae, and fecundity of flies that have experienced pupal diapause is lower than in long-day flies that have not been through diapause. The puparia of diapausing pupae contain more hydrocarbons than puparia of nondiapausing pupae, and this contributes to higher rates of net transpiration for the nondiapausing flies. Flies showing the maternal effect (short-day experience but no diapause) show an intermediate response: length of wandering, fecundity rate and quantities of puparial hydrocarbon are between the extremes observed in the other two groups of flies. Thus, the maternal effect switches the developmental programme to nondiapause, but the progeny retain some characteristics of diapause. Evidence from reciprocal crosses indicates that the photoperiodic history of the female, rather than the male, is responsible for the influence on fecundity.

Females of the flesh fly, Sarcophaga bullata Parker, produce an increasingly higher number of diapausing progeny in successive broods. Though a maternal effect completely eliminates the capacity for diapause in the first brood of females with an embryonic and larval history of short day, diapause is restored at low levels in later broods. Exposure to long daylength at the onset of adult life does not alter the diapause response of later broods, thus suggesting that the age effect cannot be modified by daylength manipulation. The age response implies that changes in maternal physiology exert an important regulatory control on the diapause fate of the pupa.

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Deuterium oxide averts pupal diapause in the flesh fly Surcophuga crassipalpis Macquart when fed t o larvae or when applied topically t o photosensitive embryos exposed to short daylength. Deuterium oxide was not effective in promoting diapause when presented t o embryos or larvae reared at long daylength. The effect of deuterium oxide appears t o be cumulative in the larval state: increasing exposure time progressively reduces diapause response. If flies reared on deuterium oxide are exposed to continuous darkness, the diapause response remains high, thus implying that the physiological capacity for diapause is not disrupted. We suggest that deuterium oxide exerts its effect on the circadian rhythm controlling diapause induction.