Abstract: Heat-shock protein 23 (hsp23) and hsp70 are both known to be strongly up-regulated during pupal diapause in the flesh fly Sarcophaga crassipalpis. This prompted us to investigate whether hsp90 was also up-regulated during diapause. To test this possibility, we developed a partial clone of a hsp90 family member for use as a probe in Northern blot hybridization. Both high and low temperature exposure up-regulated hsp90 transcripts in nondiapausing individuals. In contrast to hsp23 and hsp70, hsp90 was down-regulated following entry into diapause, and returned to prediapause levels after diapause termination. The response of hsp90 to heat shock and cold shock remained intact during diapause: both shocks evoked elevated expression. The results indicate differential regulation of hsps during diapause and in response to thermal injury inflicted on diapausing pupae.

Abstract: 1. Bumblebee colonies show much variation in the number of workers, drones, and queens produced. Because this variation prevails even when colonies are kept under identical conditions, it does not seem to be caused by extrinsic factors but rather by differences between founding queens. 2. The most likely factor that could cause differences between queens is diapause. Although colonies are raised under standardised conditions, the queens often experience diapause of different length. If there are costs associated with diapause that influence post-diapause reproduction, the diapause history of the queens could affect colony characteristics. 3. Here, several colony characteristics are compared: number of first and second brood workers; total number of workers, drones, and queens; energy spent on sexuals; sex ratio; rate of worker production; time to emergence of first reproductive; and colony lifetime. Colonies were used where the queens experienced a diapause treatment of 0 (nondiapause queens), 2, and 4 months. 4. Although no proof was found for the existence of costs associated with diapause, the colony characteristics of nondiapause queens were significantly different from those of diapause queens. Colonies of nondiapause queens produced the lowest number of workers but the highest number of young queens. 5. It is argued that these nondiapause colonies are more time-constrained than diapause colonies because nondiapause colonies produce two generations within the same season and should therefore be more efficient in producing sexual offspring. 6. Moreover, nondiapause colonies should rear a more female-biased sex ratio because they can be certain of the presence of males produced by other (diapause) colonies.

Abstract: Although there are few studies of the sexual life of coccinellids these phenomena have attracted the interest of isolated groups of coccinellidologists Probably the most important finding is that at least some coccinellid species (Adalia bipunctata and Harmonia axyridis) do not mate at random with the females prefering certain males This phenomenon was first observed in Adalia bipunctata by Lusis and then studied in detail by Majerus, O'Donald, de Jong and others In Japan, Harmonia axyridis was similarly studied by Osawa and Ueno While the former author found that in this species (as in A bipunctata) the colour of the elytra is most important in mate choice by females, the latter stresses that size and activity are important Sperm competition is another interesting phenomenon, most often the sperm of the last male fertilizes the eggs (Ueno, Katakura) Obata and Hidaka have contributed in an important way to elucidating the function of the spermatophore in mating The studies by Hodek and Ceryngier recorded the maturation and regression of testicular follicles and the relation of mating activity to diapause in four coccinellid species In contrast to females, where induction of diapause prevents maturation of ovaries, in diapausing males the tissue of testicular follicles remains active until the temperatures decrease in late autumn Dissection of spermathecae revealed principal difference in autumn mating activity between Coccinella septempunctata, in which 40-60% of the beetles mated before hibernation and Ceratomegilla (syn Semiadalia) undecimnotata, which does not mate in autumn

Abstract: Rates of protein synthesis are substantially depressed in diapause II embryos of Austrofundulus limnaeus. Inhibition of oxygen consumption and heat dissipation with cycloheximide indicates that 36% of the adenosine triphosphate (ATP) turnover in prediapausing embryos (8 d postfertilization [dpf]) is caused by protein synthesis; the contribution of protein synthesis to ATP turnover in diapause II embryos is negligible. In agreement with the metabolic data, incorporation of amino acids (radiolabeled via 14CO2) into perchloric acid–precipitable protein decreases by over 93% in diapause II embryos compared with embryos at 8 dpf. This result represents a 36% reduction in energy demand because of depression of protein synthesis during diapause. Adjusting for changes in the specific radioactivity of the free amino acid pool at the whole‐embryo level yields rates of protein synthesis that are artifactually high and not supportable by the observed rates of oxygen consumption and heat dissipation during di...

Abstract: The marine copepod Calanus finmarchicus is known to overwinter at depth in a state analogous to diapause in terrestrial insects, but the cues which cause individuals to enter and leave this state are the subject of speculation. In this paper we use a simple demographic model, driven by environmental data from 4 distinct locations in the organism's eastern range, to test the plausibility of a number of candidate mechanisms. We start from Miller et al.'s (1991; Mar Ecol Prog Ser 72:79-91) hypothesis that diapause is controlled by photoperiod, and show that thls leads to unrealistic patterns of reproductive activity in northern waters. We extend the model to include the recently reported phenomenon (Hirche 1996a; Ophelia 44:lll-128) of delayed gonad maturation in females experiencing low food concentrations. This ylelds more plausible annual patterns, but falls to reproduce observed geographical variation in the timing of the yearly onset of reproductive activity. Our final model dispenses with photoperiodic control and assumes that diapause duration is controlled by the normal development processes operating at a reduced rate. This model reproduces all the qualitative features of the patterns of reproductive activity observed at our 4 test sites, thus demonstrating that photoperiod cueing is not a necessary prerequisite for the regular re-ascension of C. finmarchicus into surface waters

Abstract: Adult diapause in Riptortus clavatus (Thunberg) was induced by short-day photoperiods, and the critical daylength for its induction was 13.5 h. When insects were reared from eggs under diapause-inducing photoperiods near the critical daylength, the duration of diapause was shorter than when reared under the shorter daylengths. Adults terminated diapause under long-day photoperiods earlier when they had been raised under a near-critical photoperiod than under shorter daylengths; this indicated that the initial intensity of diapause was dependent on the length of the inducing photoperiod. Not only the photoperiods experienced during preimaginal development but also the value of the long-day photoperiods experienced after adult emergence affected the time of onset of oviposition. When the photophase was shortened, either abruptly or gradually after adult emergence, the duration of diapause was prolonged. Diapause was long when induced by shorter daylengths than the near-critical photoperiod. Different photoperiods have thus different quantitative effects on both the initial intensity of diapause and the rate of diapause development.

Abstract: Summary 1. Parthenogenetic adults of the sycamore aphid Drepanosiphum platanoidis exhibited reproductive diapause for 4–6 weeks in the summer. 2. The diapausing aphids had small gonads (accounting for just 13% of the total aphid protein content) bearing small (< 0.5 mm long) and developmentally immature embryos. There was no evidence of embryo resorption. 3. The diapausing aphids had significantly depressed essential amino acid content and elevated glutamine content, relative to reproductively active D. platanoidis. 4. The reproductive characteristics and amino acid titres of the diapausing aphids resemble those of aphids lacking functional symbiotic bacteria. Uncoupling of maternal and embryo growth and suppression of bacterial function are proposed as key elements in the diapause of D. platanoidis.

Abstract: Microlesions of the brain were made to examine the role of neurosecretory neurons in the pars intercerebralis (PI) and pars lateralis (PL) in the induction of reproductive diapause of the female blowfly Protophormia terraenovae. Under both diapause-inducing (LD 12 : 12, 20° C) and diapause-averting conditions (LD 18 : 6, 25° C), the ovaries invariably failed to develop when the PI was removed. When the PL was removed bilaterally, the ovaries developed in most of the females, irrespective of the rearing conditions. Removal of the PL prevented females from entering reproductive diapause. These results show that certain neurosecretory neurons in the PI are necessary for vitellogenesis, and that the PL contains inhibitory neurons which suppress vitellogenesis during reproductive diapause.

Abstract: Beet armyworm, Spodoptera exigua (Hubner), is a freeze-susceptible and migratory species, but can overwinter in temperate areas without diapause. Most developmental stages reared under constant environments are able to induce a cold-hardening process in response to a brief exposure to cool temperature. In this study, we analyzed the effect of daily temperature and photoperiod cycles on the cold-hardening process. Rearing temperatures significantly affected cold tolerance of larvae. In constant temperature regimes, as rearing temperature decreased, cold tolerance increased. Cyclic temperature regimes caused a significantly higher cold tolerance than did constant temperatures with the same daily average. In cyclic regimes with three combinations of a thermophase temperature and three different cryophase temperatures below a developmental threshold (13°C), cryophase temperature had a significant effect on cold tolerance. Cold-hardening induced by rearing temperatures was associated with decreases of supercooling points and increases of hemolymph osmolalities and glycerol contents. A cyclic photoperiod produced a higher cold tolerance than did constant dark or light. There was, however, no variation in cold tolerance among different cyclic daylength regimes. These results indicate that fluctuating temperature and photoperiod significantly affected cold tolerance of S. exigua.

Abstract: A possibility of using synthetic analogues of juvenile hormone (juvenoids) to disrupt imaginal diapause of the apple blossom weevil, Anthonomus pomorum females was demonstrated. Out of three preparations tested (methoprene, fenoxycarb and W-328) methoprene and fenoxycarb appeared to be effective. Sensitivity to juvenile hormone analogues develops early after imaginal emergence (even before the female starts to feed) and lasts throughout the whole aestivo-hibernation dormancy. Although the juvenoids could stimulate the onset of oogenesis at any time during diapause, the propensity of the ovaries to form normal eggs developed only during hibernation part of the dormancy; in earlier stages of diapause accumulation of yolk was observed but matured eggs were not produced. Methoprene treatment caused marked increase of locomotory activity accompanied with decrease of dry weight, increase of water content, depletion of trehalose resources, decrease of cold hardiness and, finally, 100% mortality within four weeks in the weevils treated during their feeding or aestivation stages. Although similar changes were observed in the treated pre-feeding weevils, they later recovered and survived until next spring without apparent loss of cold hardiness. A possibility of designing a control method based on this principle is discussed and the results of small-scale field trials that support its plausibility are reported.

Abstract: We have been studying the factors that control larval diapause of Sesamia nonagrioides (Levebvre), a multivolitine pest of corn, Zea mays L., in the Mediterranean. The effect of various combinations of photoperiod and temperature on the induction of larval diapause of S. nonagrioides was examined. Short daylengths (8–12 h) were the main factor inducing diapause in this species, whereas high temperatures could avert the effect of the photoperiodic signal. Daily temperature cycles with different amplitudes (differences between the thermophase [high phase] and cryophase [low phase] temperatures), could induce diapause under a photoperiod of 12:12 (L:D) h when the cryophase coincided with the scotophase (dark period). In contrast, short daylengths had no effect on diapause when the thermophase coincided with the scotophase. Moreover, greater differences between the high and the low temperatures of the thermoperiod led to a higher incidence of diapause. Diapause also occurred under 24-h thermoperiods at constant darkness; the incidence of diapause correlated with the duration of the cryophase. The thermoperiodic response curve of diapause under constant darkness was analogous to that of the photoperiodic response of a type I, or long-day insect. The cryophase of the thermoperiod must be <17.5°C to obtain a high incidence of diapause. Consequently, it appeared that a thermoperiodic threshold during the cryophase was demonstrated. Hence, both the duration and the temperature of the cryophase of the thermoperiod were important factors controlling the diapause response. The ecological implications of this behavior are discussed.

Abstract: The cold hardiness of individuals from overwintering populations of a freeze susceptible bug Pyrrhocoris apterus from central and southern Europe differed significantly. Supercooling point (SCP) correlated well with both lethal temperature (LT50) and lethal time (Lt50), and is agood index of cold hardiness of adults during and after diapause. In January, diapause terminated, but cold hardiness was similar to that recorded in November; cold hardiness decreased slightly in March and markedly in May. Short exposure (less than a week) to higher temperatures before termination of diapause did not reduce the cold hardiness. Cold hardiness did not closely follow air temperatures.The Bulgarian bugs retained lower cold hardiness regardless of acclimation to harsh field conditions in the Czech Republic. The interpopulation difference is therefore a heritable character representing an adjustment to local climates.

Abstract: The processes involved in the induction and termination of facultative larval diapause in the parasitoid Colpoclypeus florus (Walker) was investigated in the laboratory. Larval diapause in C. florus is under maternal control. Photoperiod is the major factor governing the induction of larval diapause in C. florus. The pupa of the maternal generation is the most sensitive stage though the adult is also sensitive. Adult sensitivity increases with age, in particular at low temperatures. Photoperiod has no effect on the developing larva. The critical photoperiod for diapause induction for parasitoids maintained throughout the life cycle at 15 and 20°C was found to be 15 and 13.5 h, respectively. No diapause was induced at 25°C at any photoperiod examined. A chilling period of >5 wk is a prerequisite for diapause termination. After 8 wk at 5°C, all diapausing larvae pupate within 20 d whether held under short or long daylength. Chilling temperature and duration of chilling significantly affected diapau...

Abstract: Ontogenetic timing of photoperiodic sensitivity is critical in the life history of insects that rely on photoperiod as a token stimulus. The life stages of Orius insidiosus (Say) sensitive to photoperiod for diapause induction were investigated by transferring predators between short (10:14 (L:D) h) and long (14:10(L:D) h) constant photoperiods (at 208C) at various life stages. Bugs were considered to be in diapause if their preoviposition period exceeded 14 d after adult eclosion. The first three instars exhibited no clear sensitivity to photoperiod relative to diapause induction or intensity (as measured by preoviposition period). The fourth instar was somewhat sensitive, ap- pearing to enhance the sensitivity of subsequent stages. In contrast, the fifth instar was highly sensitive to the short photoperiod. Exposure of bugs to short photoperiods during this instar induced diapause in at least 50% of the population. Likewise, the adult stage was sensitive to photoperiod during at least the first 14 d after eclosion. Exposure to short photoperiods during the early adult stage also appears to be necessary to induce diapause in '50% of the population. In addition, short photoperiod served to maintain diapause in adult females. Transferring diapausing adults from short to long photoperiods accelerated diapause termination relative to those remaining in short photo- period.

Abstract: Although numerous studies have indicated that diapause is heritable and phenotypically plastic, none of them has examined the quantitative genetic basis of this plasticity. In this paper we report such an analysis for egg diapause in the cricket Allonemobius socius, the induction of which appears to be largely determined by the mother. We analysed the quantitative genetic basis of the phenotypically plastic response of female A. socius to age and environmental conditions. We measured the production of diapause eggs on four occasions over a 16-day period, and in two environments; one mimicking an 'early' period of the year and another mimicking a 'late' period. We analysed genetic variation in phenotypic plasticity using the character-state approach. Diapause proportion was heritable (h2 ranged from 0.17 to 0.49, being larger in the 'early' environment), and the genetic correlation between ages in proportion of diapausing eggs was close to 1 but showed a decrease with increased difference between ages. There were significant genetic correlations between environments for all ages. Because of the reduction in genetic correlation as the difference in ages increases, selection will be more effective at changing the overall shape of the reaction norm than causing local changes. Furthermore, the high genetic correlations may constrain the evolution of the reaction norm. When the two environments are converted into the estimated days in the year the two reaction norms form approximately a single curve as predicted from previous theoretical analysis of the optimal reaction norm.

Abstract: This paper is focused on diapause and polyphenism of development of Lagria hirta L. and tries to unravel its mechanism of life-history adaptation. Lagria hirta, distributed widely in Europe, has a strictly univoltine life cycle. The results showed that larval diapause and moulting polymorphism were the deciding factors that made L. hirta maintain its univoltinism and keep a flexible relation between seasonal changes and life-history phases. In the laboratory, larvae of this species were not able to pupate if kept at constant temperatures of 5 °, 10 °, 15 °, 20°, 25 ° or 30 °C combined with a photoperiod of either LD (L16:D8) or SD (L8:L16). Pupation only occurred if larvae were reared at 15 °-25 °C when intervened by a three-month chilling at 5 °C in stages L 3 , L 4 , L 5 or L 6 . A chilling treatment was shown to be obligatory for the termination of its larval diapause and had an accelerating and synchronizing effect on larval development. Larval diapause of L. hirta was characterized by no pupation and more moulting in advanced instars, longer duration of each single stage, and moulting desynchronization. Larval development was found to be variable with respect to the total number of instars: most larvae underwent a total of seven or eight moults; some larvae might even moult once or twice more, but they seldom pupated. It seemed that the choice for the 7-instar or the 8-instar development did not directly relate to any of the external conditions, such as temperature, photoperiod, and stages with chilling treatment. This polyphenism was observed in the same group under identical conditions and even in a single egg clutch. In L. hirta, overwintering in different stages of L 3 -L 6 . and choosing the 7- or 8-instar pathway of development are two features that increase the plasticity and flexibility in coordinating its life cycle with seasonal change, that varies unpredictably from year to year.

Abstract: The variation in life-history patterns that allow closely related species to co-exist has been an important theme in ecology for decades. We examined intra- and interspecific variation in a key life-history trait - diapause - for two congeneric copepods (Eudiaptomus gracilis and Eudiaptomus graciloides) inhabiting three lakes in Northern Germany. Diapause has been hypothesized in both theoretical and empirical studies to be important in the coexistence of competing species. We found no diapause for E. gracilis whereas we documented two distinct periods of diapause in the life cycle of E. graciloides. In the latter species, diapausing eggs were produced in all three lakes during autumn, however, relative investment in diapausing eggs differed between lakes. Diapausing egg production was delayed or fewer females switched to making diapausing eggs in the more productive lakes relative to the less productive systems. In the sediments of all three lakes, viable diapausing eggs were found buried from the sediment-water interface down several centimeters in each lake, suggesting the presence of a long-lived egg bank. In addition, detailed population studies carried out on both species in one lake (Schohsee) revealed a second period of diapause in E. graciloides. After the diapausing eggs are produced in autumn, females accumulate lipids, reduce feeding and apparently over-winter in a state of active diapause. The prevalence of diapause in E. graciloides and lack of it in E. gracilis raises questions regarding the factors that shape the life-histories of these congeners, and the role that the life-history differences observed may play in their coexistence.

Abstract: The recent isolation of several diapause up regulated and down regulated genes suggests two key features of diapause that are likely to prevail across species. First, far fewer genes are being expressed during diapause, thus suggesting that diapause does represent a shut-down in gene expression. Second, the fact that certain genes are expressed uniquely in diapause indicates that diapause is more than a shut-down in gene expression and represents a distinct developmental pathway. Only few diapause down regulated and up regulated genes have so far been identified, and among them are potentially important genes coding for cell cycle regulators and stress proteins. It should then be possible to determine whether common patterns of gene expression dictate diapause in different species and different developmental stages.