A nondiapausing variant of the flesh fly, Sarcophaga bullata, that shows arrhythmic adult eclosion and elevated expression of two circadian clock genes, period and timeless

We describe a variant of the flesh fly, Sarcophaga bullata, which fails to enter pupal diapause in response to short daylength and low temperatures. This fly also has an arrhythmic adult eclosion pattern: rather than eclosing in early photophase, the variant ecloses arrhythmically throughout the photophase and scotophase. The loss of both diapause (photoperiodic response) and the gating of adult eclosion (presumably a circadian response) suggests that the same clock system is involved in these two responses. An examination of the expression patterns of the clock genes period and timeless demonstrates that both genes are present in the nondiapausing variant, but surprisingly, both genes are expressed at higher levels. This abnormality we observe, possibly the consequence of an upstream clock gene malfunction or a malfunction of the autoregulatory loop, results in disruption of a component of the clock system that is apparently needed for both photoperiodism and circadian rhythmicity.     

Effects of photoperiod and temperature on reproductive diapause in Ophraella communa (Coleoptera: Chrysomelidae), a potential biocontrol agent against Ambrosia artemisiifolia

Abstract To investigate the seasonal adaptation strategies of Ophraella communa to new habitats, the effects and regulation mechanisms of photoperiod and temperature on the reproductive diapause in a population collected from Changsha, Hunan were examined. Adults showed obvious reproductive diapause, which was regulated by photoperiod and temperature. At 30°C, there was no adult diapause occurring under either long‐day or short‐day conditions; at 25°C the pre‐oviposition period was short and fecundity was high in adult females under L : D 16 : 8 h, whereas under L : D 12 : 12 h, a few females entered reproductive diapause; at 20°C under short‐day conditions, all female adults entered diapause. The pre‐oviposition period was significantly prolonged when the pupae and adults were transferred from long‐days to short‐days, but the day length influence was not obvious when they were transferred only in the adult stage. However, the fecundity dropped greatly no matter whether the photoperiod shifted to short‐days only in the adult stage or whether the shift occurred in both the pupal and adult stage. The fecundity was extremely low when photoperiod shifted from long‐days to short‐days in both pupal and adult stages. This was an indication that the pupal and adult stages were the photoperiod‐sensitive stage for adult reproductive diapause. This was especially true for the photoperiod in the pupal stage, which has a distinctly significant regulative effect on reproductive diapause. Additionally, this article also addresses the reason for different photoperiodic response patterns in reproductive diapause induction between the Changsha strain and the Tsukuba strain (Japan) of O. communa.     

Regulatory mechanisms in phenotypic plasticity of diapause and nondiapause pupal colouration of the swallowtail butterfly Papilio machaon

Nondiapause pupae of Papilio machaon L. exhibit pupal colour diphenism comprising green–yellow and brown–white types. To understand the regulatory mechanism underlying the control of pupal colouration in P. machaon, the effect of environmental cues on diapause and nondiapause pupal colouration is investigated. When larvae reared under short‐day and long‐day conditions are allowed to pupate in sites with a smooth surface and a yellow background colour, all diapause pupae exhibit a brown–white type and 89.5% of nondiapause pupae exhibit a green–yellow type, respectively. With rough‐surface pupation sites, all diapause pupae exhibit brown–white and intermediate types, whereas a large proportion of nondiapause pupae exhibit brown–white and intermediate types, although some exhibit a green–yellow type. When extracts prepared from the head‐thoracic and thoracic‐abdominal regions of larval central nervous systems are injected into the ligated abdomens of P. machaon short‐day pharate pupae, all recipients exhibit a brown–white colouration. Furthermore, when each extract is injected into the ligated abdomen of Papilio xuthus L. short‐day pharate pupae with orange‐pupa‐inducing factor activity, recipients injected with the head‐thoracic extract exhibit the brown type, whereas those injected with the thoracic‐abdominal extract exhibit an orange colour. The results indicate that the response to the environmental cues of pupation site in P. machaon changes according to the photoperiodic conditions experienced during larval stages, and that at least two hormonal factors producing brown–white pupae are located in the larval central nervous system, with the secretion of these factors being regulated by the recognition of environmental cues in long‐day larvae.     

Roles of circadian clock genes in insect photoperiodism

Functional involvement of a circadian clock in photoperiodism for measuring the length of day or night had been proposed more than 70 years ago, and various physiological experiments have supported the idea. However, the molecular basis of a circadian clock has remained veiled in insects. Nevertheless, our knowledge of the functional elements of a circadian clock governing circadian rhythmicity has advanced rapidly. Since both circadian rhythms and photoperiodism depend on the daily cycles of environmental changes, it is easy to assume that the same clock elements are involved in both processes. Recently, the RNA interference (RNAi) technique clarified that the molecular machinery of a circadian clock governing photoperiodism is identical to that governing circadian rhythmicity. Here, I review the theoretical background of photoperiodic responses incorporating a circadian clock(s) and recent progress on the molecular clockwork involved in photoperiodism in the bean bug Riptortus pedestris and other insect species. I have focused on the intense controversy regarding the involvement of a circadian clock in insect photoperiodism.     

Imidazole derivative KK-42 boosts pupal diapause incidence and delays diapause termination in several insect species

The imidazole derivative KK-42 is a synthetic insect growth regulator known previously to be capable of averting embryonic diapause in several Lepidoptera, but whether it also affects diapauses occurring in other developmental stages remains unknown. In the present study, we examined the effect of KK-42 on pupal diapause in two species of Lepidoptera, the Chinese oak silkworm Antheraea pernyi and the corn earworm Helicoverpa zea, and in one species of Diptera, the flesh fly Sarcophaga crassipalpis. In A. pernyi, KK-42 delayed pupal diapause termination under the long day conditions that normally break diapause in this species. Likewise, in H. zea, KK-42 delayed termination of pupal diapause, a diapause that, in this species, is normally broken by high temperature. KK-42-treated pupae of these two species eventually terminated diapause and successfully emerged as adults, but the timing of diapause termination was significantly delayed. KK-42 also significantly increased the incidence of pupal diapause in H. zea and S. crassipalpis when administered to larvae that were environmentally programmed for diapause, but it was not capable of inducing pupal diapause in H. zea if larvae were reared under environmental conditions that do not normally evoke the diapause response. Experiments with H. zea showed that the effect of KK-42 on pupal diapause was dose- and stage-dependent, but not temperature-dependent. Results presented here are consistent with a link between KK-42 and the ecdysteroid signaling pathway that regulates pupal diapause.     

Effects of photoperiod and temperature on diapause induction in Conogethes punctiferalis (Lepidoptera: Pyralidae)

The yellow peach moth, Conogethes punctiferalis (Guenée), a multivoltine species that overwinters as diapausing larvae, is one of the most serious insect pests on maize in China. Effect of photoperiod and temperature on larval diapause was examined under empirical laboratory conditions. Short‐day treatments caused larval diapause at 25°C, and the critical photoperiod was between 12 and 13 h (or 12 h 51 min) light per day. No sensitive instar was identified for diapause induction under alternated short‐ (L : D 11 : 13 h) and long‐day (L : D 14 : 10 h) treatments at different larval stages. However, accumulative treatment of three instars and 10 d under short‐day treatment was required for the induction of 50% larval diapause. All larvae entered diapause at 20°C, whereas less than 3% did so at 30°C, irrespective of the long‐ or short‐day treatment. Furthermore, under the short‐day treatment, more than 90% of larvae went into diapause with temperatures ≤ 25°C, but less than 17% did so at 28°C. In contrast, under the long‐day treatment, less than 19% of larvae went into diapause with temperatures ≥ 23°C. The forward shift (5°C) of critical temperature under the long‐day regime demonstrated the compensatory effect of temperature and photoperiod on diapause induction. In conclusion, C. punctiferalis had a temperature‐dependent type I photoperiodic diapause response; there was no sensitive instar for diapause determination, but the photoperiodic accumulation time countermeasures both of the short‐day cycles and the number of instars exposed, and the photoperiodic diapause response, was a temperature‐compensated phenomenon.     

Maternal influence on diapause induction in Trichogramma (Hymenoptera: Trichogrammatidae): the dynamics of photosensitivity

It is known that the prepupal diapause in Trichogramma is dependent on temperature conditions of embryonic and larval development and on the photoperiodic conditions of preimaginal development of maternal females. However, the relative photosensitivity of different preimaginal stages has been never investigated. We studied the position of the photosensitive period over the preimaginal development of maternal females in T. embryophagum Htg. and T. principium Sug. et Sor. by transferring preimaginal stages between diapause‐averting ‘long’ day (L : D = 20 : 4) and diapause‐inducing ‘short’ day (L : D = 12 : 12). Results showed that the influence of maternal photoperiod on progeny diapause was determined during the late pupal stage (last days of preimaginal development at 20°C). During this time, the critical duration of the photoperiodic induction was extremely small: one short or long day caused almost the same effect as the permanent development under these conditions. As a whole, photoperiodic response in Trichogramma was found to be unusually rapid, labile and easily reversible which is probably explained by extremely small size and fast development of these egg parasitoids. The results of this study could be used for elaboration of optimal methods for Trichogramma mass rearing and storage and for prediction of its seasonal cycles under natural conditions.     

Responses to stepwise photoperiodic changes for the larval diapause of the Indian meal moth Plodia interpunctella

Abstract The Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae) diapauses as a last‐instar (fifth) larva. At 30 °C, no larvae enter diapause under any photoperiodic conditions; at 25 °C, the photoperiodic response curve is a long‐day type with a critical length of approximately 13 h light; at 20 °C, diapause is induced moderately even under long days (> 13 h). Cumulative effects of short days or long days on diapause induction are determined by alternate, stepwise and gradually changing regimes of photoperiod at 25 °C. When the larvae are repeatedly exposed to LD 16 : 8 h and LD 12 : 12 h photoperiods every other day, the incidence of diapause is 37%. When the larvae are placed under an LD 16 : 8 h photoperiod for 2 days and then under an LD 12 : 12 h photoperiod for 1 day, it is 38 %. Exposure to an LD 16 : 8 h photoperiod for 1 day and then to an LD 12 : 12 h photoperiod for 2 days induces only 15% diapause. This may indicate that the photoperiodic information is not accumulated in a simple fashion despite the generally accepted hypothesis (i.e. photoperiodic counter). Larvae exposed to an LD 16 : 8 h photoperiod for 5 days after oviposition express a very high incidence of diapause even under short days between an LD 2 : 22 h and LD 12 : 12 h photoperiod. After 10 days exposure to an LD 16 : 8 h photoperiod, however, the short day does not induce diapause strongly. On the other hand, an LD 12 : 12 h photoperiod in the early larval life is highly effective in the induction of diapause. A gradual increase or decrease of photoperiod (2 min day^?1) shows that the direction of photoperiodic change does not affect the diapause determination.     

Differentiation in life cycle of sympatric populations of two forms of Hyphantria moth in central Missouri

Wing patterns of Hyphantria adult male moths collected in central Missouri were examined throughout the breeding season. Three major peaks of adult flight were observed: the first peak consisted mainly of adults with spotted wings, while the second and third peaks consisted of immaculate adults. Black‐headed larvae appeared in the field following the first major peak of moth flight, and red‐headed larvae appeared in the field following the second peak. Sympatric red‐headed and black‐headed forms were collected in the field and subsequently reared on an artificial diet under conditions of 16 h light : 8 h dark (LD 16:8) at 25°C. The larval period of the black‐headed form was shorter than the red‐headed, whereas the pupal period of the black‐headed form was longer than the red‐headed. Pupal development is retarded in some individuals at high temperatures in the black‐headed form. Photoperiodic response curves for pupal diapause were different between the two forms. The critical photoperiod for pupal diapause was 15 h 10 min in the red‐headed form, which was longer than that for the black‐headed form (14 h 40 min). The two forms responded to shifts in photoperiod differently. These developmental responses temporally separate the two forms in the field; the red‐headed and black‐headed forms represent a set of adaptations favoring univoltinism and bivoltinism, respectively. Red‐headed larvae fed mainly at night, while the black‐headed larvae fed without a clear day–night rhythm. Nocturnal feeding in the red‐headed form is adaptive to protection against predation, but fails to fully utilize heat units and thus to produce a second generation.     

Photoperiodic response of diapause induction in the pine caterpillar, Dendrolimus punctatus

The pine caterpillar, Dendrolimus punctatus (Walker) (Lepidoptera: Lasiocampidae), is a multivoltine pest of pine trees in China, overwintering as larvae. Winter diapause was induced by short day length. The critical night length was about 10 h 40 min at 25, 28, and 31 °C in the field, showing a temperature‐compensated diapause induction. Transfer experiments from a short night (L16:D8) to a long night (L12:D12) or vice versa at different times after hatching showed that sensitivity to day length was restricted to the first 14 days; the required day number for a 50% response at 25 °C was about 3.5 days for short nights but 7.5 days for long nights, indicating that short nights are photoperiodically more effective. When four successive short nights (L16:D8) were used to interrupt the long‐night regime (L12:D12) at different development stages and vice versa, the results showed that the highest sensitivity to photoperiod occurred on the 4th?8th day, corresponding to the second larval instar. Experiments of alternating short‐night (L16:D8) and long‐night (L12:D12) cycles during the larval period showed that the information of short nights as well as long nights could be accumulated. By rearing the larvae under conditions other than 24‐h light–dark cycles, we clearly showed that the dark period (scotophase) played a major role in the determination of diapause. The Nanda‐Hamner and Bünsow experiments failed to reveal rhythmic fluctuations with a period of about 24 h in the occurrence of diapause. Therefore, the photoperiodic clock in D. punctatus is an hourglass timer or a damped circadian oscillator.     

Relationship between photoperiod and secretion of the diapause hormone during larval stages of the silkworm, Bombyx mori L., reared on an artificial diet

The suboesophageal ganglion of the silkworm, Bombyx mori synthesizes sufficient diapause hormone to produce diapause eggs, regardless of the photoperiodic conditions experienced during the larval stages. When larvae destined to produce non-diapause eggs are implanted with the brain-suboesophageal ganglion complex from larvae which have been reared under short-day conditions, the resulting adults lay diapause eggs. The larvae receiving the complex from larvae reared under long-day conditions gave rise to adults which did not produce any diapause eggs. The brains from pupae which have been reared under long-day conditions show an activity inhibiting the secretion of diapause hormone by the suboesophageal ganglion. The mechanism through which the brain controls the secretion of diapause hormone from the suboesophageal ganglion can be modified by photoperiodic conditions during the larval stages.     

Effect of different artificial diets on diapause induction under controlled temperature and photoperiod in the silkworm, Bombyx mori L.

ABSTRACT. Embryonic diapause of the silkworm, Bombyx mori , is generally induced by temperature and photoperiod during the egg stage of the previous generation and not in the larval stage. However, when silkworm larvae are reared on an artificial diet instead of mulberry leaves, their diapause is strongly affected by temperature and photoperiod experienced in the larval stage, with a distinct long-day response for diapause induction. Moreover when larvae which have been reared on artificial diet under long-day condition are fed mulberry leaves even for a short period of time, most of the resultant female adults lay diapause eggs. These results suggest that the photoperiodic response of larvae for diapause induction may be strongly suppressed by some components in mulberry leaves.     

Phase-shifting effects of a light pulse interrupting scotophase on locomotor activity rhythm and photoperiodic time measurement for diapause in the onion fly, Delia antiqua

When a light pulse of 1 h duration was given 3 h after lights off in a photoperiod of 11 h light : 13 h dark (LD 11 : 13) at 20°C, the phase of the major peak of locomotor activity rhythm in Delia antiqua was delayed for approximately 0.6 h. In contrast, it was advanced by approximately 0.6 h by a light pulse given 9 h after lights off. It is suggested that in the circadian clock, a pulse falling in the early scotophase is taken as a new dusk and a pulse falling in the late scotophase is taken as a new dawn. Although a sharply defined critical photoperiod did not exist in the diapause response to photoperiod in D. antiqua, the percentage of pupal diapause decreased by these pulses in LD 11 : 13 at 20°C. The effect of a 15 min light pulse on both locomotor activity rhythm and pupal diapause induction was stronger at 3 h than at 9 h after lights off, while a 1 min light pulse was ineffective at both times. The parallel effects of light pulse on locomotor activity rhythm and diapause response might be based on the same chronobiological functions.     

Quantitative short-day photoperiodic response in larval development and its adaptive significance in an adult-overwintering cerambycid beetle, Phytoecia rufiventris

The chrysanthemum longicorn beetle, Phytoecia rufiventris, overwinters in the adult stage and reproduces in spring. Larvae of this beetle develop during summer inside a host stem or root. In the present study, photoperiodic control of larval development and its adaptive significance were examined in this beetle using an artificial diet. Larvae showed a short-day photoperiodic response at 25 °C with a critical day length of around 14 h; larvae reared under short-day conditions pupated, whereas those reared under long-day conditions entered summer diapause with some supernumerary molts and did not pupate. A similar response was found at 30 °C, but with a shorter critical day length. Below the critical day length, a shorter day length corresponded to a shorter larval period. Larvae transferred from long-day conditions to various photoperiods showed a similar quantitative response. Field rearing of larvae starting at various times of year showed that pupation occurs within a relatively short period in early autumn. Field rearing of pupae and adults at various times indicated that only pupation in early autumn results in a high survival rate until winter. Earlier or later pupation led to a low survival rate due to death before overwintering in the adult and pupal stages, respectively. Thus, in P. rufiventris, timing of pupation regulated by the quantitative short-day photoperiodic response is vital for survival. Relatively lower developmental threshold in the pupal stage supports this hypothesis.     

The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle,Colaphellus bowringi (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal summer and winter diapause. Its photoperiodic response highly depends on temperature. All adults entered diapause at ≤ 20 °C regardless of photoperiods. High temperatures strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting influence of short daylengths was expressed only at high temperatures (above 20 °C). This indicates that the beetle has a cryptic ability to reproduce in summer. In fact, summer and winter diapause were induced principally by relatively low temperatures in the field, whereas photoperiod had less influence on diapause induction. The critical daylength for the autumnal population was between 12 h and 13 h. By transferring from a long day to a short day or vice versa at different times after hatching, it was shown that the sensitive stage with regard to photoperiod was the larva, whereas a long day was photoperiodically more potent than a short day. The sensitive stage to temperature encompassed the larval, pupal and adult stages. This different response pattern serves to ensure that the beetle enters summer and winter diapause in time. The selections for non-diapause trait under laboratory (at 25 °C) and natural conditions (at >24 °C) showed that the beetle could lose its sensitivity to photoperiod very rapidly.     

Comparison of the circadian eclosion rhythm between non-diapause and diapause pupae in the onion fly, Delia antiqua: the change of rhythmicity

When pupae of Delia antiqua were transferred to constant darkness (DD) from light-dark (LD) cycles or constant light (LL), the sensitivity to light of the circadian clock controlling eclosion increased with age. The daily rhythm of eclosion appeared in both non-diapause and diapause pupae only when this transfer was made during late pharate adult development. When transferred from LL to DD in the early pupal stage, the adult eclosion was weakly rhythmic in non-diapause pupae but arrhythmic in diapause pupae. However, the sensitivity of the circadian clock to temperature cycles or steps was higher in diapause pupae than in non-diapause pupae; in the transfer to a constant 20 degrees C from a thermoperiod of 25 degrees C (12 h)/20 degrees C (12 h) on day 10 after pupation or from chilling (7.5 degrees C) in DD, the adult eclosion from diapause pupae was rhythmic but that from non-diapause pupae arrhythmic. In a transfer to 20 degrees C from the thermoperiod after the initiation of eclosion, rhythmicity was observed in both types of pupae. The larval stage was insensitive to the effect of LD cycle initiating the eclosion rhythm. In D. antiqua pupae in the soil under natural conditions, therefore, the thermoperiod in the late pupal stage would be the most important 'Zeitgeber' for the determination of eclosion timing.     

Haemolymph ecdysteroid titres in diapause and nondiapause larvae of the European corn borer, Ostrinia nubilalis

The ecdysteroid titres of last-instar prediapausing, diapausing and nondiapausing larvae of Ostrinia nubilalis were determined by radioimmunoassay. In the nondiapause larvae a major peak of ecdysteroid activity preceded pupation by 24 h and continued through the pupal ecdysis. This peak was correlated with head and thorax critical periods as well as with changes in behaviour and physiology marking the transition from feeding larva to prepupa. Nondiapause larvae also displayed a rise in ecdysteroid titre during the feeding phase of development. This rise was approx one tenth that of the major peak and lasted 32 h. It was not correlated with any overt changes in larval physiology or behaviour. The diapause ecdysteroid profile was distinctive in that the levels measured were all lower than the lowest of the nondiapause curve. No peaks were observed in the diapause titres. Prepupal changes such as spinning and the cessation of feeding were not correlated with any increase in ecdysteroid levels. During diapause termination, under a long-day photoperiod, no increases in ecdysteroid titre were observed for the first 10 days. After 12 days individuals began to show ecdysteroids above the diapause levels. Pupation started after 16 long days.     

Adaptive significance of the recurrent photoperiodic response in a spring‐breeding carabid beetle,Carabus yaconinus

Seasonal changes in the photoperiodic sensitivity for reproduction in adults of a spring‐breeding carabid beetle, Carabus yaconinus (Coleoptera: Carabidae), were examined by transferring adults from outdoor to photoperiodic conditions in various seasons. Newly‐emerged adults transferred to the laboratory in September to December showed a long‐day photoperiodic response, but lost photoperiodic sensitivity gradually during winter. In late April, overwintered adults were not sensitive to the photoperiod, with females continuing to have mature eggs under both long‐day and short‐day conditions. In contrast, in late June and late July, the adults were sensitive to the photoperiod, with only those kept under short‐day conditions re‐entering reproductive diapause. This recovery of photoperiodic sensitivity appears to play a definitive role in maintenance of diapause in autumn for adults that have reproduced. The adults collected in late April regained photoperiodic sensitivity in two months even after being kept under unchanged conditions. Therefore, no environmental cue is required for recovery of photoperiodic sensitivity, which apparently recovers with the lapse of time. Our results suggest that the recurrent photoperiodic response is required in long‐living adults of C. yaconinus to regulate the timing of reproduction, and also indicate a difference in photoperiodic sensitivity in summer between overwintered and newly‐emerged adults.