Opsins are involved in nymphal photoperiodic responses in the cricket Modicogryllus siamensis

The cricket Modicogryllus siamensis Chopard shows photoperiod‐dependent changes in the duration of nymphal development: nymphs become adult within 60 days after hatching, undergoing seven moults under long‐day conditions, whereas, under short‐day conditions, nymphal development takes much longer (approximately 180 days) with an increased number of moults. Because removal of the compound eyes alters this photoperiodic response, the eyes may be involved in light detection during the photoperiodic response. The role of opsins, expressed in the compound eye, is examined in the present study with reference to the photoperiodic response. Molecular cloning identifies cDNAs of three opsins, opsin‐Ultra Violet (Ms'op‐UV), opsin‐Blue (Ms'op‐B) and opsin‐Long Wave (Ms'op‐LW), and in situ hybridization reveals that the opsin genes are expressed in specific regions of the compound eye in a gene‐specific manner. RNA interference (RNAi) technology using the opsin genes results in a partial disruption in the long‐day responses; most of the treated crickets showed eight or more moults and up to 23.5% show a prolonged nymphal period that is typical of short‐day responses. Under short‐day conditions, op‐UV RNAi crickets show earlier adult development, whereas no distinct alterations are observed in op‐B and op‐LW RNAi insects. The results suggest that the opsin genes may play differential roles in the photoperiodic response in the cricket and that the results can be at least partially explained in terms of the external coincidence model of photoperiodic time measurement.     

Effects of unilateral compound-eye removal on the photoperiodic responses of nymphal development in the cricket Modicogryllus siamensis

The cricket, Modicogryllus siamensis, shows clear photoperiodic responses at 25 degrees C in nymphal development. Under long-day conditions (LD16:8), nymphs became adults about 50 days after hatching, while under short-day conditions (LD8:16) the duration of nymphal stage extended to more than 130 days. Under constant dark conditions, two developmental patterns were observed: about 60% of crickets became adults slightly slower than under the long-day conditions, and the rest at later than 100 days after hatching, like those under the short-day conditions. When the compound eye was unilaterally removed on the 2nd day of hatching, an increase of molting and an extension of the nymphal period were observed under the long-day conditions, while under the short-day conditions, some crickets developed faster and others slower than intact crickets. These results suggest that this cricket receives photoperiodic information through the compound eye, that a pair of the compound eyes is required for a complete photoperiodic response, and that interaction between bilateral circadian clocks may be also involved in the response.     

Photoperiodic and temperature control of nymphal development and induction of reproductive diapause in two predatory Orius bugs: interspecific and geographic differences

Abstract The effects of day‐length and temperature on pre‐adult growth and induction of reproductive diapause are studied in Orius sauteri and Orius minutus (Heteroptera: Anthocoridae) from northern (43.0°N, 141.4°E) and central (36.1°N, 140.1°E) Japan. In the north, at 20 °C, pre‐adult growth is slower under an LD 14 : 10 h photoperiod than under shorter or longer photophases. At 24 and 28 °C, the longer photophases result in shorter pre‐adult periods. Acceleration of nymphal growth by short days in autumn appears to be adaptive. In the central region, this response is less pronounced, suggesting that timing of adult emergence is less critical than in the north. Day length also influences the thermal requirements for pre‐adult development. The slope of the regression line representing temperature dependence of pre‐adult development is significantly smaller and the lower development threshold (LDT) is significantly lower under an LD 12 : 12 h photoperiod than under long‐day conditions. The weaker dependence of nymphal growth on temperature and the lower LDT in autumn might be adaptive. In the north, increased temperature shifts the critical day length of diapause induction and suppresses the photoperiodic response in O. sauteri but not in O. minutus. Further south, the incidence of diapause in both species is low even under short‐day conditions but the same interspecific difference is observed (i.e. increase of temperature affects the response in O. sauteri but not in O. minutus). This suggests seasonally earlier diapause induction with weaker temperature dependence in O. minutus than in O. sauteri.     

A genetic analysis of photoperiodic reproductive diapause in Drosophila triauraria

Abstract. Recombinant inbred lines were produced from hybrids between diapausing and non-diapausing strains of Drosophila triauraria Bock & Wheeler by twenty generations of full-sib mating. The analysis of these inbred lines suggests that the difference in the photoperiodic response between the original diapausing and non-diapausing strains is due to genes at three or four loci and at least one of these loci is located on the X chromosome. The original diapausing strain and two inbred lines exhibited circadian peaks when subjected to the Nanda-Hamner protocol, although they had different critical daylengths. This suggests that critical daylength is modified independently of the circadian oscillation system in this species. On the other hand, diapause duration was correlated with critical daylength among the inbred lines and the original diapausing strain, suggesting that these two traits are under the control of the same genetic system.     

Inheritance of photoperiodic induction of larval diapause in the Asian corn borer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully‐developed larvae in response to short‐day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day‐lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long‐day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day‐length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short‐day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically‐induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.     

Hourglass and oscillator expressions of photoperiodic diapause response in the cabbage moth Mamestra brassicae

Abstract. Both oscillator and hourglass features are found in the photoperiodic response that controls the pupal winter diapause of Mamestra brassicae. The expression of oscillatory response to extended long-night cycles is temperature dependent, i.e. circadian resonance appears at 23 and 25^oC but not at 20 and 28^oC. At 20^oC, scanning of extended scotophases by a short light pulse does not reveal any clear circadian rhythmicity. However, a circadian feature of the photoperiodic response is indicated even at 20^oC by a bistability phenomenon, i.e. either one of the two dark periods in symmetrical skeleton photoperiods determines the diapause response depending on the phase angle with the preceding (entraining) light-dark cycles. At 20 and 25^oC, the incidence of diapause increases as a function of the number of light–dark cycles regardless of the cycle length (T) , if T is 24 h or 2 X 24h (with a 12 h light period). A non-diel cycle (r=36h) is less effective, suggesting that disturbance of the circadian organization partly impairs the diapause-inducing function. The inductive effect of a long night is largely affected by temperature, and becomes saturated with eight cycles at 20^oC and 14 cycles at 25^oC. Presumably, an hourglass mechanism measures the dark time, and a circadian component involved in some later sequence of the photoperiodic response may or may not be expressed depending on the mode of interaction between them.     

New microsatellite loci isolated from the field cricket Gryllus bimaculatus characterized in two cricket species, Gryllus bimaculatus and Gryllus campestris

We have developed a new set of 27 polymorphic markers for each of two cricket species, Gryllus bimaculatus and Gryllus campestris. Initially, 14 published G. bimaculatus loci were tested in G. campestris; however, only five loci were polymorphic. Therefore, we isolated an additional 50 new microsatellite loci from G. bimaculatus and tested these in both species. In a minimum of 20 individuals, 27 of the new loci were polymorphic in G. bimaculatus and 25 in G. campestris.     

Cytokinins in photoperiodic induction of flowering in Chenopodium species

Changes in cytokinin (zeatin – Z, zeatin riboside – ZR, isopentenyladenine – iP, isopentenyladenosine – iPA) levels were determined under light regimes inductive and non-inductive for flowering in leaves, stems, roots and apical parts of short-day Chenopodium rubrum and long-day Chenopodium murale. In leaves. stems and roots of both plant species the level of cytokinins (in C. rubrum of Z and ZR, in C. murale of Z. ZR, iP and iPA) decreased by about 50% during the dark period and increased again during the subsequent light period, No significant changes in cytokinin levels were observed in continuous light. In apical parts of C. rubrum cytokinin level (Z, ZR, iP) was dramatically increased (by 400–500%) at the end of the dark period and decreased to about the original value during the following light period, while no changes were observed in continuous light. In apical parts of C. murale the level of cytokinins doubled during floral induction consisting of 10 days of continuous light. A red (R) break (15 min at the 6th h of darkness), which prevents flowering in C. rubrum , has no significant effect on cytokinin levels in leaves at the end of darkness. Cytokinin levels increased 1 h after R and decreased again rapidly. On the other hand, the increase of cytokinin level in the apical parts of C. rubrum was largely prevented by the R break. These effects of R on cytokinin levels were not reverted by far-red (FR), while the effect on flowering was reverted. It may be concluded that there is no correlation between changes in cytokinin levels in leaves. Stems and roots and photoperiodic flower induction, as both species, representing different photoperiodic types, showed similar changes under the same light regime. The increase of cytokinin levels in apical parts of both photoperiodic species during floral induction suggests a role (increased cell division and branching) for cytokinins in apex evocation.     

Postembryonic development of mating behavior in the male cricket Gryllus bimaculatus DeGeer

Summary The intact male nymph cricket, Gryllus bimaculatus DeGeer, was found to show mating-like behavior, that is, courtship-like behavior (CSLB) and copulation-like behavior (CPLB), in the 7th and 8th (last) instars. The 8th instar nymph exhibited less CSLB and CPLB than the adult but much more than the 7th instar nymph. The movement patterns of CSLB and CPLB were essentially the same as those of adults except for motor acts requiring the use of the genitalia. CSLB was short and often ceased spontaneously before it switched to CPLB. CPLB also ended earlier than in adults. The occurrence of CSLB and CPLB was almost zero the few days around ecdysis. The nymph was very sensitive to disturbance, so that he often stopped courtship for more than 30 min after stimulation. CSLB was similarly induced in the male nymph (8th instar) by pairing with a female adult, male adult, female nymph (8th) and male nymph (8th). The female nymph (8th) was observed to mount not only the male adult but also the male nymph (8th). A fixed time sexual refractoriness forming a basis of cyclical mating activity was not present after CPLB in the nymph. It appeared in association with the emergence of spermatophore protrusion behavior around day 3 after the imaginal molt. In fledglings, there were some transitions during the sexual maturation process, such as failures in hook hanging, spermatophore extrusion, and spermatophore transfer to the female. The decerebration experiments on nymphs and fresh adults agreed with behavioral observations. These results suggest that the development of mating behavior in the male cricket is a process of enhancement of basic motor patterns but not a process of addition of new movements by changes in pattern generation circuits in the central nervous system.Abbreviations CPLB copulation-like behavior - CPPT interval between copulation and spermatophore protrusion - CSCP interval between calling song and copulation - CSLB courtship-like behavior - CSS courtship song - PTCS interval between spermatophore protrusion and calling song - SPE spermatophore extrusion     

Geographical variation and inheritance of the photoperiodic response controlling larval diapause in two distinct voltine ecotypes of the Asian cornborer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) enters facultative diapause as fully‐grown larvae in response to short day lengths during autumn. As a result of geographical variations in photoperiodic response, the moths from Nanchang (28.8°N, 115.9°E; NC strain) judge both LD 14 : 10 h and LD 15 : 9 h photocycles as long days and develop directly, whereas moths from Haerbin (44.9°N, 127.2°E; HB strain) judge the same photocycles as short days and enter diapause. Crosses between the two strains are used to evaluate the inheritance of diapause. The critical day lengths for diapause induction in the HB strain are significantly longer than those in the NC strain at all temperatures. The critical day length of F₁ progeny is intermediate between the two strains. However, the critical day length in all crosses is significantly longer with HB strain fathers or grandfathers than with NC strain fathers or grandfathers, indicating that the male parent has significantly more influence on the critical day length of subsequent progeny than the female. The results from all crosses under LD 14 : 10 h or LD 15 : 9 h photocycles at 25 °C show that the inheritance of diapause in O. furnacalis does not fit a purely additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance. The incidence of diapause for F₁ progeny under an LD 14 : 10 h photocycle is significantly higher than that under an LD 15 : 9 h photocycle, suggesting that the induction of diapause can be influenced by interactions between the F₁ genotype and photoperiod.     

The role of circadian clock genes in the photoperiodic timer of the linden bug Pyrrhocoris apterus during the nymphal stage

Many insects survive seasonal adversities during diapause, a form of programmed developmental and metabolic arrest. Photoperiodically regulated entry into diapause allows multivoltine insect species to optimize the number of generations. The molecular mechanism of the photoperiodic timer is unknown in insects. In the present study, we take advantage of the robust reproductive diapause response in the linden bug Pyrrhocoris apterus and explore the fifth‐instar nymphal stage, which is the most photoperiod‐sensitive stage. The nymphs display daily changes in locomotor activity during short days; this differs from the activity observed during long days. We find evidence of cyclical expression of the circadian clock genes, per and cyc, in nymphal heads; in addition, per expression is also photoperiod‐dependent. The RNA interference‐mediated knockdown of the two circadian clock genes, Clk and cyc, during the nymphal stage results in reproductive arrest in adult females. Furthermore, Clk and cyc knockdown induces the expression of the storage protein hexamerin in the fat body, whereas the expression of vitellogenin diminishes. Taken together, these data support the involvement of circadian clock genes in photoperiodic timer and/or diapause induction.     

In vitro maintenance and sperm development in the testis of the house cricket (Acheta domesticus)

Summary

Whole testes of Acheta domesticus were maintained in vitro for up to 48 h. Development of sperm could not be induced in the penultimate stage testis irrespective of hormone influence. A partial stimulation of spermatogenesis in the ultimate stage testis was achieved using 10^?6 M 20-hydroxyecdysone but completion of spermiogenesis was not seen.     

Effect of temperature on photoperiodic response in a selected 'non-diapause' strain of Pyrrhocoris apterus (Heteroptera)

Abstract. The artificially selected 'non-diapause' strain of Pyrrhocoris apterus (L.) (Heteroptera) showed no diapause response to photoperiod at 26°C (Socha & Hodkova, 1994). However, the diapause response to short-day photoperiod (LD 12:12 h) became apparent at lower temperatures of 17°C (70% diapause) or 20°C (41% diapause). Diapause was induced in 60% females by short-day photoperiod combined with thermoperiod of 26/16°C, whereas only 20% diapause was induced by the same thermoperiod under continuous darkness. Thus the time-measuring system was not removed by artificial selection but the diapause response was shifted to lower temperatures. The diapause response to short days seems to be favoured rather by low temperature during scotophase than by low temperature throughout the whole light/dark cycle. If the percentage of diapause at 26°C is compared in F₁ hybrids and in wild and selected parental strains the diapause appears to be dominant at LD 13:11 h but recessive at LD 11:13 h and LD 10:14 h. A hypothesis is proposed that the inheritance of the percentage of diapause in F1 hybrids is determined by interactions of genes controlling the temperature dependence of photoperiodic response.     

变化光周期对丽斗蟋(Velarifictonus ornatus)若虫发育的影响

为弄清湖南株洲丽斗蟋若虫的季节适应策略,研究了恒定及变化光周期对其若虫发育的调控。结果表明,丽斗蟋若虫发育明显受变化光周期的影响。25℃温度条件下,3个光周期条件下的若虫发育都较慢,羽化也极不整齐,长日条件(LD 16∶8h)、中间日照条件(LD 14∶10h)和短日条件(LD 12∶12h)的若虫发育历期(mean ± SD)分别为(206.2± 44.0)d、(236.6±93.3)d和(230.3±47.4)d,若虫从开始羽化到供试个体全部完成羽化所需时间分别为216、301和156d,经历短日条件的若虫转移至长日条件后能够促进其快速发育,羽化也很整齐,反方向转移则会抑制若虫发育,且羽化也不整齐。30℃温度条件下,恒定长日条件下的若虫发育明显快于短日条件,变化光周期对若虫发育的调控与25℃相类似。变化光周期对若虫发育的影响与光周期的变化方向及低龄若虫感受的光周期类型有关。丽斗蟋若虫复杂的光周期反应模式的生态意义在于调节其生活史与季节同步。     

Constant rate allocation in nymphal development in species of Hemiptera

Abstract. This study investigated the existence of rate isomorphy (the constant allocation of relative times to different stages of development under different abiotic conditions) in Macrolophus pygmaeus (Hemiptera: Miridae; a phytophagous and predatory insect). Replicated data were used from a range of temperatures regarding (i) the developmental period of each nymphal stage in relation to the total duration of nymph development, when feeding on three host plants either with different prey species or without prey, and (ii) its egg, total nymphal and preoviposition period, on two host plants, with different prey species. The proportion of time required for the development of each nymphal stage of M. pygmaeus is not different among the temperatures or the kind of food available. These proportions ranged among the different host plants, temperatures and prey presence/absence from 17.3–21.8% in the first, 14.5–18.8% in the second, 14.2–18.3% in the third, 16.5–21.0% in the fourth and from 25.4–30.6% in the fifth nymphal stage. Thus, temperature does not significantly affect the proportion of time spent in each nymphal stage and rate isomorphy exists in nymphal development. This phenomenon was also investigated using data from the literature, and it also occurs in several other Hemiptera species. Therefore, there appears to be a constant time allocation in the nymphal development of the higher taxonomic groups of insects. However, for M. pygmaeus, rate isomorphy does not hold when considering egg‐to‐egg development and the relative duration of times to egg hatch, total nymphal development and preoviposition period. The ecophysiological implications of this rate isomorphy phenomenon are discussed in relation to endocrinological mechanisms. Apart from its theoretical interest, the existence of rate isomorphy simplifies studies on the rate of development and the estimation of thermal constants of an insect, which are essential for the prediction of insect population dynamics. It is also proposed that the term ‘rate isomorphy’ does not strictly describe the phenomenon, and it is suggested that ‘constant rate allocation’ would be a more suitable term.     

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.     

Response to nigh interruption in photoperiodic determination of wing form of the ground cricket Dianemobius fascipes

ABSTRACT. In the ground cricket Dianemobius fascipes (Walker), the occurrence of long- or short-winged form is determined by photoperiod during larval development. The pattern of this response is similar to that of diapause induction in other insects with a clearly defined critical nightlength (11.5 h). In symmetric skeleton regimes formed by a pair of 1 h light pulses, the critical nightlength is about 2 h longer than in the complete photoperiod. The long-night (short-wing) effect is eliminated by an interrupting light pulse. This response to night interruption shows only one peak in scotophases of various lengths and can be related to the critical nightlength before or after interruption. The light-reaction time required for the interruption effect changes during the night. In the early scotophase, 1 h of light is enough but 15 min fails to reverse the long-night effect, while a light pulse of only 1 min is effective about 1 h before the critical nightlength is reached. Several possible interpretations of this change are discussed.     

Photoreceptors and signals in the photoperiodic control of development

Many plant species are sensitive to changes in the seasons, especially with regard to their reproductive behaviour. Sexual or vegetative reproductive structures are often only formed at times of the year when days are sufficiently long, or short. Plants perceive daylength in the leaves, but reproductive changes occur in shoot apices in response to the movement of signals throughout the plant. There is good evidence that phytochrome A is an essential component of the daylength-sensing mechanism in long-day plants, and preliminary evidence suggests a potential interaction between phytochrome C and daylength sensitivity in short-day plants. The sensitivity of reproductive processes to photoperiodic control is directly altered by photoreceptor action, particularly in the case of phytochrome B, which has a major influence on whether flowering or tuberization occurs under non-inductive conditions in both long- and short-day plants, but is not involved in daylength measurement. The signals which move from leaves to the sites of reproductive development are not known, but there is good evidence that gibberellins may be important and some preliminary indication that brassinosteroids might also be involved in photoperiodic signalling.     

Genetic analysis of diapause capability and association between larval and pupal photoperiodic responses in the flesh fly Sarcophaga similis

Abstract A variant of the flesh fly Sarcophaga similis, which does not enter pupal diapause even under diapause‐inducing conditions, is established by artificial selection. Interline crosses of the wild‐type and the variant revealed that the diapause capability is inherited in an incomplete dominant manner. Neither sex linkage nor a maternal factor is involved in the mode of inheritance. Genetic and genetic–environmental interactions are involved in the induction of diapause. In the wild‐type, the post‐feeding larval period is prolonged in response to short days. However, in the variant, the duration of the larval period under short‐day conditions is identical to that under long‐day conditions. Long‐day responses under short‐day conditions at both the larval and pupal stages in the variant indicate that the responses are established by common factors in both stages. The factors causing the long‐day responses under short‐day conditions at different developmental stages in the variant remain to be identified. However, it is plausible to hypothesize that common factors regulate ecdysteroid release at both the larval and pupal stages, and that malfunction of the system regulating these factors triggers such ecdysteroid release, irrespective of the photoperiod. Hence, the photoperiodic responses disappear in the variant in both stages. The adult stage of the variant has a functional circadian clock, suggesting that the nondiapause phenotype is not necessarily involved in malfunction of the circadian clock.     

Heterogeneity and tissue specificity of tropomyosin isoforms from four species of bivalves

Heterogeneity and tissue specificity of tropomyosin isoforms obtained from four species of bivalves (Scapharca broughtonii (ark shell), Mytilus galloprovincialis (mussel), Atrina pectinata (surf clam) and Crassostrea gigas (Pacific oyster)), were examined. Tropomyosins were extracted from translucent and opaque portions of posterior adductor muscle, respectively, and cardiac muscle of each bivalve. There were two tropomyosin isoforms in the ark shell, the surf clam and the Pacific oyster. They were designated as TMa and TMb. In the ark shell, TMa was the common isoform and TMb was specific for the opaque portion of the adductor muscle. In the surf clam, TMb was the common isoform present in all tissues. TMa was found only in the translucent portion of muscle. In the Pacific oyster, TMb was the major component in both portions of adductor muscle and TMa was the major component in cardiac muscle, although both tropomyosins were included in all tissues. The mussel had only one tropomyosin.