Photoperiodic Response Curve Research Articles

Pigment Dispersing Factor Is a Circadian Clock Output and Regulates Photoperiodic Response in the Linden Bug, Pyrrhocoris apterus.

Daily and annually cycling conditions manifested on the Earth have forced organisms to develop time-measuring devices. Circadian clocks are responsible for adjusting physiology to the daily cycles in the environment, while the anticipation of seasonal changes is governed by the photoperiodic clock. Circadian clocks are cell-autonomous and depend on the transcriptional/translational feedback loops of the conserved clock genes. The synchronization among clock centers in the brain is achieved by the modulatory function of the clock-dependent neuropeptides. In insects, the most prominent clock neuropeptide is Pigment Dispersing Factor (PDF). Photoperiodic clock measures and computes the day and/or night length and adjusts physiology accordingly to the upcoming season. The exact mechanism of the photoperiodic clock and its direct signaling molecules are unknown but, in many insects, circadian clock genes are involved in the seasonal responses. While in Drosophila, PDF signaling participates both in the circadian clock output and in diapause regulation, the weak photoperiodic response curve of D. melanogaster is a major limitation in revealing the full role of PDF in the photoperiodic clock. Here we provide the first description of PDF in the linden bug, Pyrrhocoris apterus, an organism with a robust photoperiodic response. We characterize in detail the circadian and photoperiodic phenotype of several CRISPR/Cas9-generated pdf mutants, including three null mutants and two mutants with modified PDF. Our results show that PDF acts downstream of CRY and plays a key role as a circadian clock output. Surprisingly, in contrast to the diurnal activity of wild-type bugs, pdf null mutants show predominantly nocturnal activity, which is caused by the clock-independent direct response to the light/dark switch. Moreover, we show that together with CRY, PDF is involved in the photoperiod-dependent diapause induction, however, its lack does not disrupt the photoperiodic response completely, suggesting the presence of additional clock-regulated factors. Taken together our data provide new insight into the role of PDF in the insect’s circadian and photoperiodic systems.

Photoperiodism of Male Offspring Production in the Water Flea Daphnia pulex.

Photoperiodism is a biological seasonal timing system utilized to regulate development and reproduction in organisms. The freshwater micro-crustacean Daphnia pulex displays environmental sex determination, the precise physiological mechanisms of which are largely unknown due to the lack of an experimental system to induce female or male offspring production by alterations of the rearing environment. We recently found that D. pulex, WTN6 strain, produces female or male offspring in response to long-day or short-day conditions, respectively. Taking advantage of this system, here we report the photoperiodic response curve for male offspring production, showing 12 hours as natural critical daylength (50% incidence of male-producing mothers), and that male offspring inducibility is highly sensitive to photoperiodic alterations. By using monochromatic light emitting diode (LED) devices, we found that the effective wavelength is red-light (627 nm), which stably induces male offspring production. This suggests that the red-light photoreceptor may be decisive in the primary step of sex determination process in this strain. Our findings provide the first insights into photoperiodism and red-light as key factors in triggering male offspring production in daphnids.

Diapause induction and termination in the small brown planthopper, Laodelphax striatellus (Hemiptera: Delphacidae).

The small brown planthopper, Laodelphax striatellus (Fallén) enters the photoperiodic induction of diapause as 3rd or 4th instar nymphs. The photoperiodic response curves in this planthopper showed a typical long-day response type with a critical daylength of approximately 11 h at 25°C, 12 h at 22 and 20°C and 12.5 h at 18°C, and diapause induction was almost abrogated at 28°C. The third stage was the most sensitive stage to photoperiod. The photoperiodic response curve at 20°C showed a gradual decline in diapause incidence in ultra-long nights, and continuous darkness resulted in 100% development. The required number of days for a 50% response was distinctly different between the short- and long-night cycles, showing that the effect of one short night was equivalent to the effect of three long nights at 18°C. The rearing day length of 12 h evoked a weaker intensity of diapause than did 10 and 11 h. The duration of diapause was significantly longer under the short daylength of 11 h than it was under the long daylength of 15 h. The optimal temperature for diapause termination was 26 and 28°C. Chilling at 5°C for different times did not shorten the duration of diapause but significantly lengthened it when chilling period was included. In autumn, 50% of the nymphs that hatched from late September to mid-October entered diapause in response to temperatures below 20°C. The critical daylength in the field was between 12 h 10 min and 12 h 32 min (including twilight), which was nearly identical to the critical daylength of 12.5 h at 18°C. In spring, overwintering nymphs began to emerge in early March-late March when the mean daily temperature rose to 10°C or higher.

Effects of constant and changing temperature conditions on diapause induction inHelicoverpa armigera(Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.

Effect of photoperiod on immature development and diapause induction in the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae)

The diapause response of the Kanzawa spider mite (KSM), Tetranychus kanzawai, was examined. KSMs were reared in aluminum bottles at 18°C with different combinations of light and dark periods created by the light-control unit. The developmental periods for all immature stages tended to decrease as the light period increased. The photoperiodic response curve for diapause induction showed that the critical (=50% diapause) light period was around 13 h days(-1). No diapause induction was observed when the light period was longer than 13.5 h days(-1) or under continuous light. At 13-h days(-1) light period, the developmental period for deutonymphal stage as well as for the total immature stages was longer in diapaused females than in non-diapaused females. These results indicate that immature development as well as diapause induction are affected by photoperiod and further suggest that diapause-inducing stimuli prolong the developmental period especially for the deutonymphal stage of KSMs.

Diapause-inducing signals prolong nymphal development in the two-spotted spider miteTetranychus urticae

Female two-spotted spider mite Tetranychus urticae are grown under different photoperiods and the photoperiodic regulation of diapause is examined. The photoperiodic response curve for diapause induction was of the long day–short day type, with critical day lengths (CDLs) of 2 and 12.5 h; diapause was induced between these CDLs. The preimaginal period is significantly longer in diapausing females than in non-diapausing females; moreover, a significant positive correlation is detected between diapause incidence and deutonymphal period. Diapause incidence is high when long-night photoperiods are applied against a background of continuous darkness in the stages including the deutonymph; this stage appears to be the most sensitive to photoperiod. These observations suggest that diapause-inducing conditions inhibit nymphal development, particularly in the deutonymphal stage when photoperiodic time measurement for determination of reproduction or diapause is carried out.

Reproduktive Isolation, ökologische Sonderung und morphologische Differenz der Zwillingsarten Panorpa communis L. und P. vulgaris Imhoff und Labram (Insecta, Mecoptera)

Reproduktive Isolation, ökologische Sonderung und morphologische Differenz der Zwillingsarten Panorpa communis L. und P. vulgaris Imhoff und Labram (Insecta, Mecoptera)

Effects of skeleton photoperiods on the induction of larval diapause in the Indian meal mothPlodia interpunctella

The Indian meal moth Plodia interpunctella Hubner (Lepidoptera: Pyralidae) may measure night length to determine its developmental programme with respect to entering diapause or continuing development in the last-larval instar. Its photoperiodic clock appears to be hourglass-like, in that the response to a symmetrical skeleton photoperiod consists of two 2-h light pulses. If the insects read this as lights-on and lights-off signals, an oscillator should be involved in the clock system. In the present study, the insects are maintained under a normal photoperiod for 1 day at 25 and 20 °C and then transferred to the skeleton photoperiod or constant darkness (DD) for 1, 2 or 3 days. These photoperiodic regimes are repeated during the larval sensitive stage. There is no difference in the percentage diapause between the effects of skeleton photoperiod and DD treatment. At 25 °C, the incidence of diapause is relatively low under very short days ( 14-h main photophase) days and relatively high under a 12-h main photophase. At 20 °C, the percentage of diapause is generally high under any photoperiodic treatment. Diapause is prevented slightly under LD 14 : 10 h and 16 : 8 h photoperiods. If the diapause clock is an oscillator that damps rapidly, under DD or constant light (LL) for 5–15 days, it may stop its oscillation but, after exposure to the skeleton photoperiod, the clock system might be reset. There is no difference in the diapause-inducing effect between the skeleton and normal photoperiodic treatments after DD. The incidence of diapause is moderately high under short days ( 16 h). On the other hand, when the insects are exposed to the skeleton photoperiod after LL, the induction of diapause is low, regardless of the interval between the two light pulses in skeleton photoperiods. Under normal photoperiodic conditions after LL, a clear photoperiodic response curve is obtained. Thus, P. interpunctella does not show any sign of the oscillatory function in the night-time measurement and is regarded as being ‘hourglass-like'.

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 (&gt; 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.

Photoperiodic response curves for plasma LH concentrations and age at first egg in female broiler breeders

The objective of this work was to define precisely the response curve for photoinduced luteinizing hormone (LH) release in feed-restricted meat-type (broiler) breeder females and to compare it with the photoperiodic response curve for advance in age at first egg (AFE). Birds with a mean body weight of 2.0 kg at 20 weeks of age were transferred from an 8 to a 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 14 or 18-h photoperiod; change in plasma LH was measured 4 d after photostimulation and subsequent individual AFE recorded. The first significant increase in LH secretion was seen in birds transferred to an 11.5-h photoperiod, but no further significant increases in LH were observed in birds transferred to longer photoperiods. A photoperiodic response curve based on a meta-analysis of changes in photoinduced LH secretion observed in this study and data from an earlier experiment using dwarf broiler breeders indicated a critical daylength of about 9.5 h and a saturation daylength of approximately 13 h. Similarly, the first significant advance in AFE occurred in birds transferred to an 11-h photoperiod, but with no further significant increases seen in birds transferred to photoperiods >11 h. A response curve for photoinduced advances in AFE was produced by meta-analysis using data from the present study and from an earlier investigation involving fewer, more widely spaced photoperiods. It is concluded, in female broiler breeders, that the photoperiodic response curves for photoinduced LH release and AFE are similar, with the point at which the responses begin to rise steeply (classical critical daylength) occurring at 9.5 h and the asymptote (classical saturation daylength) at 13 h. Functionally, however, the minimum photoperiod to achieve a significant change in either LH secretion or advance in AFE is between 11 and 11.5 h.

モンシロチョウPieris rapae crucivora Boisduval（チョウ目：シロチョウ科）の蛹休眠を誘起する光周反応の地理的変異

The photoperiodic response curve for pupal diapause induction of the white cabbage butterfly, Pieris rapae crucivora Boisduval was determined in several populations of the Japan Archipelago. Larvae were reared under different photoperiods ranging from 8L16D to 16L8D at 20±0.5°C. The critical photoperiods for pupal diapause induction were 14 h 40 min for the Iwamizawa population (43°10′N), 13 h 15 min for the Sendai population (38°15′N), 13 h 10 min for the Nagaoka population (37°23′N), 12 h 08 min for the Okayama population (34°39′N), 11 h 50 min for the Matsuyama (33°50′N) and Kagoshima (31°35′N) populations and 11 h 15 min for the Naze population (28°23′N). The critical photoperiod increases as latitude increases. This result suggests that adaptation to a cool climate in a higher latitude region shifts the critical photoperiod for pupal diapause induction towards a longer range. The developmental zero for the larval stage in the Sapporo (43°03′N) and Matsuyama populations was calculated as 9.8°C and 9.6°C for the larval stage, respectively. These results are discussed in relation to seasonal adaptation for each population.

Evolutionary significances of cryptic variation in the reaction norm of photoperiod sensitivity of rice (Oryza sativa L.)

Patterns of photoperiodic-response curve (PRC) of heading time in rice were examined using the five near-isogenic lines (NILs) of Taichung 65, in which insensitive alleles was replaced by photosensitive alleles through backcrossings. In the first experiment, the NILs showed the diversified patterns of PRC, depending on genotype, under the controlled conditions (9-, 10-, 12- and 14-h daylengths). In addition, the two NILs with different Se1 alleles showed the different patterns although they showed similar heading times under natural daylength (NDL) conditions. The cryptic difference gives some clues as to the relationship between the patterns and heading-time behaviors under NDL conditions. In the second experiment, behaviors of vegetative and reproductive developments under 20-h daylength condition with high- and low-nutrient conditions were examined to know whether or not they behave as expected from their PRC obtained in the first experiment. Under the extremely long-day condition, the photosensitive alleles brought about long-growth durations where the internal changes for senescence might drastically occur with increases of total number of phytomers (TNP) and decrease potentials for reproductive developments. The nutrient levels might not affect the pattern of internal changes but might affect TNP, depending on genotype, and as a result, the nutrient levels might bring about different developmental fates in the same genotype under the long-day condition. The present results suggest the importance of genotype-by-environment interaction in relation to the cryptic variation of PRC in rice.

Geographic variation in photoperiodic response for the induction of pupal diapause in the Aristolochia-feeding butterfly Atrophaneura alcinous

The photoperiodic response curve for pupal diapause induction of the butterfly Atrophaneura alcinous was determined in several temperate and subtropical populations of the Japan Archipelago at 20°C, using Aristolocia debilis leaves as larval food. Altitude and host plant use also differed among them. For the temperate populations of Kiire, Kashihara, Fuchu, Yokosuka and Yamagata, the critical photoperiod increased with latitude, and the subtropical Ishigaki population showed the shortest critical photoperiod. Further, a change in the shape of photoperiodic response curve, but no shift in the critical photoperiod, was found in a mountain population of Kiire, giving a high incidence of diapause in long photoperiods. These results are discussed in relation to latitude, altitude, and host plant.

Phenotypic evolution and the genetic architecture underlying photoperiodic time measurement

A wide variety of higher plants, vertebrates, and arthropods use the length of day to synchronize growth, development, reproduction, dormancy, and migration with the changing seasons. In the pitcher-plant mosquito, Wyeomyia smithii, critical photoperiod mediating the onset and maintenance of larval diapause has evolved about 10 standard deviations in mean critical photoperiod between the ancestral, Gulf Coast populations, and the derived, Canadian populations. We are seeking to understand how this evolution has been accomplished at both the genetic and the physiological levels. At the genetic level, average heterozygosity at protein-coding loci decreases with latitude of origin, while genetic variation for photoperiodic response increases with latitude of origin, particularly within the formerly glaciated regions of North America. Hybridization experiments reveal widespread genetic differences in critical photoperiod due to epistasis. We ascribe the increase in genetic variation in photoperiodic response, despite directional and stabilizing selection to the contrary, to the release of additive from epistatic variance during successive founder events in W. smithii's northward dispersal following recession of the Laurentide Ice Sheet, and to the resulting genetic drift and reorganization of genetic architectures in descendent populations. At the physiological level, northern populations of W. smithii, as well as northern populations of spider mites, flies, moths, and beetles in both North America and Europe show a declining expression of the rhythmic component of photoperiodic response. In Drosophila melanogaster, when the epistatic coupling between the period locus and photoperiodic response is disrupted, the critical photoperiod is shifted towards shorter daylengths; analogously in W. smithii, when epistatic interactions are disrupted in the recombining generations of hybrid populations, the critical photoperiod is shifted towards shorter daylengths. The implications here are (1) that in W. smithii, it is the epistatic modification of the photoperiodic response curve by the circadian clock that is being disrupted in the recombining generations and (2) that post-glacial range expansion into the North-Temperate Zone by arthropods in general may involve uncoupling of the circadian and photoperiodic clocks. Despite the tremendous advances that have been made in understanding circadian rhythmicity at the molecular level, virtually nothing is known about how or whether any of the downstream ‘clock-controlled genes’ connect with photoperiodic time measurement. Except in W. smithii, little is known about how this connection changes with seasonal adaptation of photoperiodic response through evolutionary time. It is our goal and desire that our top–down approach to the evolution of photoperiodic time measurement will meet and mesh with the bottom–up approach that is being developed so fruitfully for circadian clocks.

Geographical Variation in Photoperiodic Response for Diapause Induction Between Univoltine and Multivoltine Populations ofKytorhinus sharpianus(Coleoptera: Bruchidae)

The northern Aomori (univoltine) and southern Mitsuma (multivoltine) populations of the bruchid beetle, Kytorhinus sharpianus (Bridwell), were reciprocally transplanted. The incidence of diapause was significantly different between the northern (88.9%) and southern populations (0%) at the southern location. The critical photoperiods for diapause induction at the late 4th instar were determined in 4 latitudinally separated populations at 24°C. The critical photoperiod increased from 14.5:9.5 to 15.2:8.8 (L:D) h toward the north. The difference in the incidence of diapause between the Aomori and Mitsuma populations at the southern location can be explained by the difference in the critical photoperiod. However, the photoperiodic response curve in the northern univoltine population (Aomori) was shallower than that in the 3 southern multivoltine populations (Obanazawa, Kujiranami, and Mitsuma). In addition, the variation in the photoperiodic response within the univoltine Aomori population was larger than within the multivoltine Mitsuma population. These large differences in the photoperiodic response curve and its variation may be explained by a large change in natural selection of the critical photoperiod between the univoltine and multivoltine populations.

An actographic study of diel activity in the semelparous polychaete Nereis (Neanthes) virens Sars in relation to the annual cycle of growth and reproduction

Summary Photoperiod has a profound influence on the life cycle of Nereis (Neanthes) virens coordinating the transition from somatic growth to reproductive development. Here we report on a rapid method to characterize the diel component of the photoperiodic response and characterize the photoperiodic response curve. The diel emergence activity of the semelparous polychaete Nereis (Neanthes) virens Sars has been investigated by means of an automated actograph. Emergence events were recorded for every second of real time and the number of events per hour analyzed over periods of up to 5 consecutive days under a variety of photoregimes. There is a marked nocturnal pattern of activity. The number of excursions from the burrow system is high during the night reaching near zero shortly after dawn. Excursions from the burrow system during daylight hours were much less frequent. The total number of emergence events per 24 h was significantly higher under LD 16:8 than under LD 8.16 even though the period of dark, when spontaneous emergence mainly occurs, was longer. The actographic records suggest that under LD 8:16 the feeding behaviour of the animals is substantially reduced compared with that observed under LD 16:8. A photoperiodic response curve has been obtained where there is a critical LD cycle around LD 11:12 and a progressive increase in emergence rate between LD 12:12 and LD 16:8. The mean number of emergence events per day is directly related to the duration of the photophase and inversely related to the scotophase duration although emergence mainly occurs during the night.

Photoperiodic induction of diapause in the spider mite Tetranychus urticae: qualitative or quantitative time measurement?

Abstract. Insects and mites may measure photoperiods eitfier by classifying them as long or short relative to a critical value (qualitative time measurement) or by using the absolute value (quantitative time measurement). The spider mite Tetranychus urticae is thought to use a qualitative mechanism of time measurement. In this paper we present the results of experiments with an inbred line of the spider mite (to keep genetic variation in photoperiodic responses small), to test whether quantitative aspects also play a role. Differences in diapause incidence in different long‐night photoperiods at different temperatures may be an indication of quantitative responses to photoperiod.The effect of temperature on the photoperiodic response curve was studied at 16oC, 19oC and 22oC. The response curves appeared to be similar at 16oC and 19oC, with a critical nightlength between 10 and 11 h. At 22oC, diapause induction was less than 100% in all long‐night regimens and die critical nightlength had shifted to 12 h. Maximum diapause induction (93%) occurred in a light‐dark cycle with a 16 h dark phase (LD 8:16 h). Diapause induction was lowest in long‐night photoperiods with dark phases of 20 h and longer.The number of light‐dark cycles needed for 50% diapause induction at 19oC varied. between 12.1 and 14.7 for LD 6:18 h, between 10.9 and 12.5 for LD 8:16 h, between 10.6 and 11.6 for LD 10:14 h, and between 10.1 and 10.7 for LD 12:12 h. Independent of die light‐dark regimen, diapause induction took place in some individuals after receiving 8 cycles and virtually all individuals entered diapause after 16 cycles.No effect was found of the photoperiodic treatment during prediapause development (LD 6:18 h, LD 8:16 h, LD 10:14 h, LD 12:12 h) on diapause duration. The average diapause duration at LD 10:14 h and 19oC was 61 days over all four treatments.We explained the results by hypothesising that nightlengths are assessed qualitatively and mat the photoperiodic clock operates more accurately near the critical nightlength.

Rhythmic components of photoperiodic time measurement in the pitcher-plant mosquito, Wyeomyia smithii.

Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause is positively correlated with latitude (r 2 = 0.977) among six populations from southern (30-31° N), intermediate (40° N), and northern (46-49° N) latitudes in North America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude, so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14 (T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying circadian pacemaker.

Effects of Temperature and Photoperiod on the Induction of Diapause and the Determination of Body Coloration in the Bean Bug, Riptortus clavatus

Abstract The incidence of diapause and details of body coloration were examined in adults of the bean bug, Riptortus clavatus (Thunberg) (Heteroptera, Alydidae) under various photoperiodic and temperature conditions. The insects showed a long-day photoperiodic response for the induction of diapause at 20, 25 and 30°C. However, some adults at 30°C failed to enter diapause even under short-day conditions. A photoperiodic response that produced light-colored adults under long-day conditions was common among 20, 25 and 30°C, although high temperature increased the proportion of light-colored adults. The photoperiodic response curve for the induction of diapause and that for in the determination of the coloration of the lateral metathorax exhibited a high degree of similarity at 20, 25 and 30°C, supporting a common time-measurement system for these two responses. With respect to the coloration of the ventral metathorax, temperature rather than photoperiod was the major determinant, although an effect of photop...

Photoperiodic time measurement and a graded response in a cockroach.

Almost exclusively, photoperiodic insects respond to a given photoperiod in one of two ways: a "long-day" response or a "short-day" response. Intermediate responses occur only at a very restricted range of photoperiods (often less than 30 min) and are generally population phenomena rather than intermediate responses of individuals. In contrast, individuals of the wood roach, Parcoblatta pennsylvanica, show intermediate responses over a broad range of photoperiods. We examined the effect of constant light, constant darkness, and photoperiods ranging from 10 to 18 hr of light per 24 hr on growth rate as measured by weight gain, and found a robust photoperiodic response. Nymphs raised in photoperiods with light periods (photophases) from 0 to 12 hr gained little weight, whereas those in LD 18:6 were almost 15 times heavier. This is the first report of a photoperiodic response curve for a cockroach. Interestingly, there was a linear relationship between the duration of the photophase and weight gain over a broad range of photoperiods (LD 12:12 to LD 18:6; r2 = 0.99). Statistical analysis showed that the intermediate responses were attributable to individuals' growing at an intermediate rate. Another interesting observation was that all larval stages appeared to be capable of perceiving and responding to photoperiodic signals. The results of further experiments using non-24-hr photoperiods were consistent with the existence of a circadian component in the photoperiodic time measurement in this species.