The control of ovarian development during adult diapause in the cabbage whitefly, Aleyrodes proletella

ABSTRACT. Field collections of overwintering cabbage whitefly, Aleyrodes proletella L. (Homoptera: Aleyrodidae) taken during the autumn and winter of 1982/83 and 1983/84 have shown that ovarian development proceeds at a low, but near uniform rate throughout diapause. Extensive fat body is recorded during the autumn and early winter of both periods, but this gradually diminishes during February and March. There does not appear to be a true refractory phase during the dormancy. A period of chilling primes the females for accelerated ovarian development in favourable conditions. When field collected females were transferred to light: dark 16:8 h (15°C) or L:D 12:12 h (15°C) in the laboratory, the subsequent rates of ovarian development were not significantly different, suggesting that temperature is the major regulator of the activation phase, although there was some evidence to suggest that an increase in photoperiod also has a role.     

Differential photoperiodic responses in genetically identical winged and wingless pea aphids, Acyrthosiphon pisum, and the effect of day length on wing development

Abstract. Winged and wingless individuals of a pink clone of the pea aphid, Acyrthosiphon pisum (Harris), showed differences in the response curves for photoperiodic induction of both males and sexual females (oviparae). The critical night length (CNL) for ovipara induction in winged aphids was 0.75 h shorter than in wingless aphids, whereas the CNL for male induction in winged aphids was 1.0h longer than in wingless aphids. This means that in winged aphids the CNL for male induction in winged aphids was 0.5 h longer than that for ovipara induction, while in wingless aphids the CNL for male induction was 1.0–1.5 h shorter than that for ovipara induction, and also the shapes of the curves differed.
Winged aphids were produced by wingless mothers which were crowded as young adults. However, when young adults were crowded in long nights, winged aphids were not produced, and the CNL for wing inhibition was between 9.5 and 10h. This effect of photoperiod on wing induction was maternal.     

First evidence for photoperiodic regulation of the life cycle in a millipede species, Polydesmus angustus (Diplopoda: Polydesmidae)

The hypothesis that the periods of dormancy previously described in the millipede Polydesmus angustus may be photoperiodically induced diapauses was tested experimentally. In this species, biennial individuals exhibit two successive periods of dormancy: aestivation in the penultimate stadium (stadium VII) and reproductive dormancy in the adults, which emerge in autumn. It was first established that the reproductive dormancy is not a thermally controlled state of quiescence. When adults emerging in autumn were kept at 16 °C under natural photoperiod, their reproduction was delayed for several months in comparison with adults emerging in spring at similar temperatures. This indicates that the reproductive dormancy begins with a period of diapause. Further experiments provided evidence of a photoperiodic induction of the adult diapause. When millipedes were reared under short day length (L:D 12:12 h) throughout their development, they required more time to reproduce than millipedes reared under long day length (L:D 16:8 h) at the same temperatures. Photoperiod influenced reproduction in females, but no significant effects were detected in adult males. On the other hand, stadium VII was markedly longer at L:D 16:8 h than at L:D 12:12 h in both sexes, which strongly suggests that aestivation is also induced by photoperiod. However, the effects on the duration of stadium VII varied among individuals, some of which showed no response to long days. This study is the first to document photoperiodic regulation of the life cycle in the class Diplopoda, a trait common in other classes of terrestrial arthropods.     

Inverse relationship between diurnal rhythms in plasma levels of thyroid hormones and pineal arylalkylamine-N-acetyltransferase (AANAT) activity in an air-breathing fish,Clarias gariepinus

Plasma levels of thyroid hormones (T₄ and T₃) and pineal AANAT activity exhibited prominent diurnal rhythms during all the four phases (quiescent, progressive, breeding, and regressive) of the fish, Clarias gariepinus. During all the four phases, we observed that (i) the acrophase (peak) of the circadian rhythm of both T₃ and T₄ occurred around midday, while the acrophase of AANAT activity rhythm was recorded during midnight, (ii) a significant negative correlation existed between plasma levels of the thyroid hormones and AANAT activity, and (iii) a direct relationship existed between water temperature/daylength and plasma levels of thyroid hormones, and an inverse relationship between water temperature/daylength and AANAT activity. On the basis of these findings, we conclude that an inverse relationship exists between the diurnal rhythms in plasma levels of thyroid hormones and pineal AANAT activity. The observed inverse relationship between the levels of thyroid hormones and pineal AANAT activity seems to be maintained by seasonal changes in water temperature and daylength.     

Novel masking effects of light are revealed in Drosophila by skeleton photoperiods

Here, we show that in a skeleton photoperiod where all midday light is removed from a standard laboratory 12:12 LD photoperiod, a large diurnal peak of activity is revealed that is continuous with the E peak seen in constant dark (DD). We further show that the circadian clock gene tim regulates light-dependent masking of daytime activity, but the clock gene per does not. Finally, relative to wild-type flies, mutants for both of these clock genes showed increased nighttime activity in the skeleton photoperiod but not in the standard photoperiod. This result suggests that nighttime activity is suppressed by the intact circadian clock, and in its absence, by exposure to a standard photoperiod. These results support and extend the literature addressing the complex interactions between masking and clock-controlled components of overt circadian rhythms.     

Diapause induction in Trichogramma embryophagum Htg. (Hym., Trichogrammatidae): the dynamics of thermosensitivity

It is known that the low temperature is the most important factor inducing the pre-pupal diapause in Trichogramma species. The position of the thermosensitive period over the life cycle and temporal variation of the degree of responsiveness were investigated in T. embryophagum Htg. by transferring pre-imaginal stages between 'neutral' temperature of 15°C and 'diapause-inducing' temperature of 10°C. Our experiments showed that 6 days long exposure at 10°C significantly increased the percentage of diapausing pre-pupae when started during rather large part of development: from embryo up to early pre-pupa. The highest thermosensitivity was recorded during the embryo and the larval stages, with some decrease during the hatching period. Treatments with shorter cold exposures (2–3 days) gave similar results. Even 24 h long exposure at 10°C increased the percentage of diapausing pre-pupae when applied during egg or early larval stage. Being started at the same stage of development, longer cold exposures caused stronger increase in the percentage of diapausing individuals. The experiments did not reveal any significant daily changes in thermosensitivity: at 12 : 12 h light : dark, larvae subjected to the low temperature during six photophases showed practically the same percentage of diapausing individuals as those subjected to the low temperature during six scotophases, and as those subjected to the 3 days long uninterrupted cold exposure. Hence, in natural conditions even occasional short-term cold periods could be accumulated.     

Scoto/photo‐periodic responses of a sub‐tropical finch (Spotted munia) in relation to seasonal breeding cycle

Abstract

Effects of continuous light and dark periods and long and ultrashort photoperiods on the gonadal function of a subtropical finch, Spotted munia, hitherto considered “non‐photosensitive”, were studied. This bird seems to be unique in that while gametogenesis and hormone production are stimulated by the continuous or long scoto periods the endogenous rhythm of reproduction continues in constant 24hr or 15hr long daily photoperiod.     

A photoperiod gene regulates vitellogenesis in Lymnaea peregra (Mollusca: Gastropoda: Pulmonata)

Summary

Populations of the fresh-water snail Lymnaea peregra from different localities vary in their capacity to lay eggs, responding either to long day or to short day photoperiods. These responses are genetically determined by a single gene locus with the long day allele dominant over the short day allele. Although previtellogenic stages of oogenesis are not affected by an inhibitory photoperiod, vitellogenesis is essentially shut down. The volumes of the dorsal bodies, which are endocrine organs that mediate vitellogenesis, are significantly smaller in snails maintained in an inhibitory photoperiod. Implantation of cerebral ganglia with attached dorsal bodies, both from egg laying animals and from dormant animals that have the potential to lay eggs in the postoperative photoperiod, into snails that were inhibited by insufficient photoperiod resulted in a significant increase in vitellogenesis in the ovotestes of the hosts. An increase in host dorsal body volume was also observed. The photoperiod gene appears to control some aspect of the cerebral ganglion that activates the dorsal body to produce a hormone that stimulates vitellogenesis in the ovotestes. Photoperiodic control of reproduction may be a factor contributing to the diverse life history strategies observed in this species.     

The regulation of development during diapause in Ephestia elutella (Hübner) by temperature and photoperiod

Diapausing larvae of Ephestia elutella reared at 20°C in short photoperiods (LD 11:13), and then maintained 12 weeks or longer at 5–15°C before transfer to 20 or 25°C, pupated sooner than unchilled controls. At 25°C, all samples kept in long photoperiods (LD 15:9) survived better and pupated faster than similarly treated samples held in short photoperiods (LD 9:15). Samples kept at 20°C after chilling pupated much slower than those at 25°C, and, except after exposure at 5°C, pupated at similar rates at LD 11:13 or 15:9, although mortality was higher at the shorter photoperiod. After exposure at 5°C, larvae required increased day-length as well as increased temperature to hasten pupation whereas after exposure at 10°C most responded to increased temperature only.For samples maintained in slightly heated or unheated outbuildings, the summer emergence was poorly synchronized and males on average emerged ahead of females. Samples moved from the unheated outbuilding to 25°C and long days in the laboratory in early spring, however, pupated quickly and males and females emerged together. A late phase of diapause development thus exists requiring both high temperature and long photoperiods to ensure a prompt resumption of morphogenesis. Spring temperatures in the United Kingdom are seldom high enough to synchronize the completion of diapause.     

Seasonal changes of thyroid hormones in field-collected Atlantic cod in relation to condition indices, water temperature and photoperiod

Serum T₄ and T₃ in wild Atlantic cod Gadus morhua ranged from 1 to 12 ng ml⁻¹ and from 2 to 27 ng ml⁻¹ respectively over a 3-year period. In general, the concentrations increased from summer (T₃) or early autumn (T₄) to maxima in mid-winter and declined abruptly during spring. The T₄/T₃ monthly means were lowest in summer and highest in winter. The seasonal patterns of thyroid hormones were weakly correlated with changes in water temperature. However, both T₄ and T₃ co-varied simultaneously with photoperiod. In addition, T₃ was correlated with the hepatosomatic index and condition factor during summer and autumn. It is suggested that the seasonal changes in the release of T₄ from the thyroid were photoperioddriven, and that the course of T3 was regulated by the metabolic state of the fish during the somatic growth period.