Abstract: This review considers in a selective way the literature on diapause in parasitic nematodes, concentrating on four species of animal parasites and three species of plant parasites. We define diapause as a developmental arrest which is temporarily irreversible, so development will not resume, even under favourable conditions, until some intrinsic changes have been completed. Our analysis recognises four stages in diapause. The first is induction, typically brought about by environmental signals (although diapause may be genetically programmed independently of the environment). These environmental signals typically do not have an immediate effect on development, but we recognise a second phase, which we call the diapause pathway, in which worms have been induced to enter diapause at a later developmental stage. Surprisingly, entry into the diapause pathway may under some circumstances be reversible. The third stage is diapause development, a period during which development is suspended, but some ill-understo...

Abstract: It has been well established that eggs of insects, including those of the silkworm Bombyx mori, contain various ecdysteroids and the amounts of these ecdysteroids fluctuate during embryonic development. In order to know the function of egg ecdysteroids in embryonic development of B. mori, we examined the biological activities of various egg ecdysteroids by in vitro ligand-binding assay and bioassay using B. mori eggs. First, using the ecdysteroid receptor of B. mori (BmEcR-B1/BmUSP heterodimer) prepared by yeast and Escherichia coli expression systems, the interaction between the ecdysteroid receptor and various egg ecdysteroids of B. mori was analyzed. The relative binding affinities of egg ecdysteroids to the BmEcR-B1/BmUSP heterodimer decreased in the order of 20-hydroxyecdysone > 2-deoxy-20-hydroxyecdysone > 22-deoxy-20-hydroxyecdysone > ecdysone > 2-deoxyecdysone > ecdysone 22-phosphate. Next, several egg ecdysteroids of B. mori were injected into the prospective diapause eggs, which show a very low level of free ecdysteroids at the onset of embryonic diapause (gastrula stage). Approximately 7% of them (P < 0.002, chi(2)-test) developed beyond the gastrula stage without entering diapause by the injection of 20-hydroxyecdysone (25 ng/egg). In contrast, the injection of other ecdysteroids was not effective in inducing embryonic development. These results suggest that 20-hydroxyecdysone, via the ecdysteroid receptor, is responsible for the developmental difference between diapause and non-diapause in B. mori embryos. Furthermore, it was suggested that continuous supply of 20-hydroxyecdysone may be required to induce embryonic development.

Abstract: 1. The survival of cyclopoid copepods was investigated in a floodplain for 2 years where flooding occurred during the cold season. The cyclopoid community was studied in three waterbodies with distinct hydroperiods: a permanent pond connected to the flooded area during inundation, a temporary pool that is part of the flooded area and an isolated temporary pool. 2. Field studies, including data obtained from samples of water, sediment and soil, showed the overall predominance of species with a summer diapause over those with a winter diapause or without diapause. Emergence of cyclopoid copepods at the onset of flooding, examined using emergence traps and data from recently filled or still isolated temporary pools, showed that some species can survive several months of drying. 3. The ability of the diapausing fourth copepodid stages of Cyclops strenuus and C. insignis, the two cyclopoids most abundant during winter and spring flooding, to survive terrestrial conditions was tested in laboratory experiments. Both species survived for several months, but rates differed among the species. A higher percentage of C. strenuus survived for a longer period, possibly explaining why this species was relatively more abundant in more temporary habitats. 4. Both dormancy and dispersal facilitated survival of cyclopoid copepods in transient habitats connected to each other during flood periods. Dormancy was the most important survival strategy, whereas dispersal could be more important following prolonged periods without flooding.

Abstract: The induction and termination of pupal diapause of Helicoverpa armigera were examined in three local populations from Kagoshima, Okayama and Ishikawa in Japan. Pupae in diapause retained eyespots for much longer than non-diapause pupae, and for markedly diverse durations. Once eyespots disappeared at the end of diapause, the period required for development until eclosion was more or less constant at 18°C. In all experiments repeated twice under the same conditions, male pupae generally showed a high tendency to enter diapause while female pupae showed a slight and rather population-specific tendency towards diapause. This trait as well as the higher intensity of male pupal diapause and the shorter post-diapause period of females suggest that females emerge first in the field in spring. This feature was regarded to be potentially important for considering the life-history strategy of this cosmopolitan pest.

Abstract: Photoperiodic responses and their adaptive significance were examined in Riptortus clavatus (Heteroptera: Alydidae), Plautia crossota stali, Dolycoris baccarum, Aelia fieberi, Nezara viridula, Nezara antennata, Graphosoma rubrolineatum, Dybowskyia reticulata, and Eurydema rugosum (Heteroptera: Pentatomidae) in the Kyoto-Osaka area, central Japan. All of these species overwinter as adults in diapause. Although they have similar feeding habits, their photoperiodic responses were quite different. Riptortus clavatus, P. c. stali, D. baccarum and N. viridula showed long-day photoperiodic responses with critical daylengths between 13 and 14 h, and were assumed to have three generations per year. The photoperiodic responses of the other five species were different both from those of the above species and from each other. These results suggested that A. fieberi and N. antennata produce two generations per year, and G. rubrolineatum, D. reticulata and E. rugosum have one or two generations per year. Nezara antennata showed a long-day-short-day photoperiodic response with summer adult diapause, which may avoid production of heat-susceptible nymphs in the hottest season. With the exception of N. antennata, the photoperiodic responses resulting in fewer generations were shown to be adaptations to dietary conditions in the field.

Abstract: Diapause in adults of the African brown ear tick Rhipicephalus appendiculatus is dependent on latitude and stock origin. Lower latitude populations, that is, those nearer the equator, show no diapause response to long or short day exposure. Diapause response to short daylengths is found in higher latitude populations, further south, and increases with increasing latitude. Nearly all individuals in the southernmost population, used in this study, enter diapause under short and long day exposure which implies that the onset of diapause in this population is obligatory. Diapause termination in higher latitude populations is induced by increasing photoperiod, further north, but still south of the equator, diapause is terminated by ageing. The differences in diapausing behaviour of the different populations are discussed in relation to their climatic conditions.

Abstract: 1. Under natural conditions in Kyoto, Japan, the reproductive activities of Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae) decreased in summer and the species showed a bimodal life cycle. 2. In the laboratory, most adult pairs raised at 20 degrees C under a LD 12:12 h regime reproduced when provided with a piece of chicken. In adults raised at 20 degrees C under a LD 16:8 h regime, however, both reproductive behaviour and ovarian development were reduced. It is concluded that these adults entered a reproductive summer diapause. 3. High temperature (25 degrees C) also suppressed the reproductive behaviour even under a favourable LD 12:12 h regime. In the field, therefore, adults reduce their reproductive activity in summer because of diapause induced by long-day photoperiods and direct inhibition of reproduction by high temperatures. 4. When the temperature was changed from 20 degrees C to 25 degrees C immediately after hatching of larvae, they reached the wandering stage in 95% of adult pairs. When the temperature was changed from 20 degrees C to 25 degrees C immediately after oviposition, however, no larvae hatched in 85% of pairs. Egg mortality was significantly higher at 25 degrees C than at 20 and 22.5 degrees C; no eggs hatched at 27.5 degrees C. The physiological mechanisms for reducing reproduction probably prevent the beetles from inefficient oviposition in summer.

Abstract: The large white butterfly, Pieris brassicae, has an unusually complex life-history in its southernmost range in Western Europe. This complexity results (1) from two developmental rests, a short-day induced hibernation and a long-day induced estivation response, and (2) from the exceptionally early appearance of the first adult generation in January/February and a subsequent winter diapause in some of their progeny. It was found that in spring and autumn, different generations are faced with critical photophases which induce hibernation or estivation, with the consequence that in five out of six generations per year, only some develop directly whereas the others enter a dormancy phase. To assess the implications of this high number of optional responses on the generation succession, the development time was studied at various photoperiods and temperatures. The results showed that a threshold response determines the duration of estivation. With unchanged summer conditions (daylengths ≥15 h) estivation lasts on average 18–19 weeks, while with autumn conditions (daylengths ≤14 h) it lasts only 7 weeks. A change of photophases from ≥15 h to ≤14 h terminates estivation within about 3–5 weeks, slightly depending on the pupal exposure time in summer conditions. The duration of estivation is not affected by temperature or by the photophases experienced by the caterpillars. The winter diapause lasts 18–19 weeks on average with winter conditions (12°C/10.30 h light), but only 8–10 weeks with late spring conditions (21°C/15 h light). These results were used to assess the effects on the population phenology, with the finding that despite the different developmental pathways, a desynchronization of the generation succession is largely prevented. Estivation, hibernation, and direct development at different seasons are well adjusted to a common phenological pattern of a continuously reproducing population. This pattern of activity covers a cryptic dormant subpopulation, and could not have been deduced by field observations.

Abstract: We studied pupal diapause maintenance and termination in Endopiza viteana, a pest of commercially grown grapes. We observed considerable variation in diapause intensity, which ranged from 5.5 to 10 mo under natural temperatures and photoperiods. Adult males tended to emerge from diapause slightly earlier than females, suggesting that E. viteana may be protandrous. In the field, low temperatures maintained diapause in overwintering pupae, and adult emergence began at ≈148 degree-days accumulated from 1 January. Photoperiod did not influence diapause termination in E. viteana. Overall, most adults emerged in spring at roughly the same time, regardless of the date at which pupae entered diapause; however, emergence was extended over a 6-wk period. Moreover, eggs oviposited by late-emerging females may experience photoperiods that would lead to diapause in pupae. Under natural conditions, extended adult emergence may result in overlapping generations; accordingly, coordinating the timing of control t...

Abstract: Seasonal adaptations were studied in a partially bivoltine population of Poecilocoris lewisi that overwinters as nymphs. Under short-day conditions, the final (5th) instar nymphs entered diapause, whereas under long-day conditions they emerged as adults within 2 weeks. The critical daylength for induction of the nymphal diapause was between 14 and 15 h at 25°C in the Osaka population. P. lewisi entered diapause in the adult stage also, under long-day conditions. Adults emerging in late spring started oviposition only after July. Insects transferred from long-day to short-day conditions at adult emergence began to lay eggs earlier and more synchronously than those kept continuously under long-day conditions due to prevention of the adult diapause. The critical daylength for induction of the adult diapause was also between 14 and 15 h at 25°C, as in the induction of nymphal diapause. The dogwood Cornus controversa, a principal host plant of P. lewisi, did not develop seeds until early July. Therefore, this suggests the absence of host plant seeds in late spring is the ultimate factor for the evolution of adult diapause in P. lewisi.

Abstract: Laboratory studies were conducted to verify the influence of photophase on diapause incidence in the Neotropical brown stink bug, Euschistus heros (Fabr., 1798), fed with soybean [Glycine max (L.)] Merrill pods. Nymphs were maintained at three different photophases: 10 h, 12 h, and 14 h, with constant temperature of 25 ± 1oC and relative humidity of 65 ± 5%. With 14 h, aproximately 100% of the adults showed mature reproductive organs; the shoulder (spine) length was significantly greater (2.96 and 2.79 mm for females and males, respectively) than those of bugs maintained at the photophase of 12 h (2.60 mm for females and males) and 10 h (2.59 and 2.53 mm for females and males). At the longer photophase (14 h), E. heros showed better reproductive performance and greater feeding activity than insects reared at 10 h and 12 h; in all photophases bugs tended to reduce feeding from the 1st to the 6th week of life. Body color was considered an unreliable parameter to indicate diapause incidence. However, at 14 h, 60% of the insects were dark brown and 40% were reddish brown. These results indicate that E. heros enters reproductive diapause with photophase of 12 hours or less, showing immature reproductive organs or with intermediate development, with shoulder (spine) less developed and reduced feeding activity.

Abstract: The role of the thermophotoperiod on larval diapause induction and development of Sesamia nonagrioides was investigated under laboratory conditions. The incidences of diapause by TC 12 : 12 thermoperiods under DD, in which the thermophase was 30°C and cryophases varied from 10 to 25°C, were compared to the effects of thermophotoperiods with the same configuration. Higher incidences of diapause were recorded when larvae were exposed to thermophotoperiods with cryophases of 15-25°C, than under thermoperiods under constant darkness. In addition, larvae exhibited significantly lower percentages of diapause when exposed to cryophases < 15°C under either thermo- or thermophotoperiodic condition. Diapausing larvae when exposed to photoperiods 16L : 8D h and different temperatures of 25-30°C proceeded to development in 14-16 days. Moreover time needed for the pupation of diapausing larvae after their transfer to 12L : 12D h, was reduced from approximately 49 to 12 days depending on temperatures of exposures (25-30°C). Diapause termination was also compared under 12L : 12D h and constant temperature of 25°C or a thermoperiod of TC 12:12 (30°: 20°). Days needed for pupation at constant temperature or under the mentioned thermoperiodic regime, were approximately the same when the high temperature of the thermoperiod coincided with the scotophase, while with the co-occurrence of the high temperature of the thermoperiod and the photophase significantly additional time was needed for diapause development. Significantly shorter time was also needed for diapause development after exposure of diapausing larvae to continuous light, than to continuous darkness under 25°C. Thermoperiods of different amplitudes with the same mean temperatures proved that the higher temperature of scotophase led to higher rate of diapause development in spite of the relatively low temperature of the photophase tested. It is suggested that thermoperiod could hasten the time needed for diapause development, but it is not the crucial factor for the termination of diapause.

Abstract: A covariation between wing morphology and diapause occurrence has been observed in many insect species, but the genetic basis of this covariation has never been established. This study measures the heritability of, and genetic correlation between, these two ecologically important threshold traits in the cricket Gryllus veletis. A total of 81 full-sib families were reared in the laboratory to estimate these parameters. A comparison of laboratory and field samples showed that these two traits are highly plastic. The heritability of wing morphology was 0.25 (0.09), the heritability of diapause occurrence was 0.77 (0.11) and the genetic correlation between them was 0.61 (0.19). These estimates did not differ between males and females. The significance of these quantitative genetic parameters is discussed with reference to the monomorphism of natural populations of G. veletis for diapause occurrence and with reference to the trade-off between the ability to disperse by flight and the ability to diapause found in at least one closely related species. A survey of the literature reveals that genetic correlations between diapause occurrence or wing morphology and various other traits are common in insects, suggesting that these two traits are often genetically integrated in insect life-histories.

Abstract: Overwintering pupae obtained from early and late emerging blueberry maggot populations were kept at similar temperatures to determine if phenological differences are caused by initial exposure to different temperature conditions in the soil after pupation. The effect of temperature and duration of exposure on time to emergence was determined by dividing pupae of each population into two cohorts placed at 20 or 25°C. Subsequently, at periodic intervals, samples were first transferred to 5°C for 6 mo to ensure diapause completion, and later kept at 20°C to measure time to emergence. In addition, we studied postdiapause pupal temperature-dependent development of the late population under laboratory and field conditions, and compared rates of development at constant temperatures and outdoors using degree-day emergence models. Longer exposure of pupae to similar temperature conditions did not decrease differences in time to emergence between populations. In the early population, there were no differences in postdiapause development with relation to temperature exposure, but in the late population, pupae exposed to 25°C emerged slower than pupae exposed to 20°C. In both populations, longer exposures to high temperature after pupation resulted in slower postdiapause development. Also in the late population, 52% of individuals emerged after 60 d exposure to 25°C, without going through diapause. Field pupal development of the late population was characterized by longer postdiapause than the early population. The presence of a transient change in the temperature-development rate relationship, observed during outdoor postdiapause development in July, was also apparent from degree-day model predictions. This developmental slowdown had not previously been observed in any Rhagoletis species.

Abstract: Rice water weevil, Lissorhoptrus oryzophilus Kuschel, overwinters as an adult in reproductive diapause. We compared the cold tolerance between diapausing and reproductive adults, and analyzed their polyol contents. Diapausing adults showed significantly higher survival rates in response to −10°C than did reproductive adults. Reproductive adults acclimated to low temperature in the laboratory also showed enhanced cold tolerance, but were not as cold-hardy as the diapausing adults. Mean supercooling points were not significantly different between diapausing and reproductive adults with a range between −15°C and −18°C. Seven polyols consisting of four sugars (glucose, trehalose, fructose, and sucrose) and three sugar alcohols (glycerol, sorbitol, and mannitol) were identified from field and laboratory adults and quantified by an ionexchange HPLC with an electrochemical detector. Glucose and trehalose were the major sugar polyols and showed the greatest change in autumn field populations. Reproductive populations kept high glucose contents during summer, while diapausing populations had high trehalose contents during winter. Coldacelimated weevils also elevated trehalose contents. Most sugar alcohols, however, were relatively low except in May when the sorbitol content of the weevils increased significantly. These results indicate that the diapausing rice water weevil, a freeze-susceptible species, is cold-tolerant with elevated trehalose content.

Abstract: A temporally structured model that enables simulation of the development of the west Japan type yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe), at different locations was developed. Life history parameter values incorporated into the model were estimated by laboratory rearing experiments. To validate the present model, the development of eggs laid monthly from June 1 through November 1 was simulated under dynamic temperature and photoperiod conditions at Ayabe City. The individuals laid on June 1 did not enter diapause but emerged in early August of the same year. On the other hand, about 2/3 of the individuals laid on July 1, and all those laid on August 1 and September 1 entered diapause (or quiescence), and started to emerge in late May of the following year. Individuals laid on October 1 and November 1 overwintered as young larvae (1st–3rd stadia) and eggs, respectively, and the majority of these emerged in late July–early August. Interestingly, the remaining individuals entered diapause in the 2nd year and emerged in June of the 3rd year. Analyses of these simulation results suggested that concentrated emergence of P. hilaris can occur twice in one year (in late May–early June and in late July–early August) at Ayabe, and this is fairly concordant with known adult prevalence at this location considering the long life-span of adults. It was also suggested that although P. hilaris at Ayabe has basically a univoltine life cycle with a facultative diapause, varying proportions of the population appear to have a bivoltine life cycle or a semivoltine life cycle depending on the meteorological conditions of that year. The life cycle of P. hilaris is suggested to be very flexible and adaptive to environmental fluctuations.

Abstract: Studies were conducted between 1996 and 1997 in Northern Ghana on the dry season survival tactics of the millet stem borer Coniesta ignefusalis (Hampson). Results confirmed that the main survival tactic employed by the insect was larval diapause, which lasts from November to May the following year. In both years, diapause termination occurred in the field 4-6 weeks after the resumption of the rains, depending on the year and location. Larval mortality rate was high during diapause with peaks occurring towards the end of the dry season in May. During the 2 years, larval populations declined by at least 50% between the start of diapause and its termination. No parasitoids were encountered during the study period, suggesting that biocontrol agents are probably not very important in the population dynamics of the insect. The implications of these findings for management of the pest are discussed.

Abstract: We describe a method for the rearing of the oligophagous herbivore Hadena bicruris, and its gregarious koinobiont endoparasitoid Microplitis tristis under laboratory conditions With flowers from the host food plant Silene latifolia available, female moths lay on average 414 eggs during their lifetime, starting at day 3 after eggression and with a peak number per night on day 8 Caterpillars can be reared with 56 % survival on an artificial diet Individually mated parasitoids succesfully parsitised individually presented L4 caterpillars Clutch size of the reared parasitoids (134) is lower than clutch sizes found in natural populations (177) Age of the females might be an important factor influencing clutch size Diapause is differently induced in the host and in the parasitoid Under long day conditions low night temperature induces diapause in hosts but not in prasitoids Under short day conditions both species enter diapause at low night temperature

Abstract: 1 There is confusion in the literature concerning a possible reproductive diapause in the adult white pine weevil Pissodes strobi. 2 We evaluated the effects of temperature, photoperiod, feeding substrate and mating status on the sexual maturation and oviposition of female white pine weevils. 3 Less than 30% of female P. strobi became sexually mature and laid eggs without experiencing dormancy under a temperature regime of 2 °C for 4 weeks. 4 Among the females that experienced a cold temperature treatment after emergence, 80% laid eggs after dormancy when exposed to a long-day (LD 16 : 8 h) photoperiod and 17.6% laid eggs when exposed to a short-day (LD 8 : 16 h) photoperiod. 5 Significantly more eggs were laid by all the females (with and without a cold treatment) when subjected to a long-day photoperiod compared with a short-day photoperiod. 6 A period of cold temperature followed by exposure to a long-day photoperiod with warmer temperatures is required to break reproductive diapause and to obtain a good oviposition response in female P. strobi. 7 This study reveals the existence of much intraspecific variation in the response of the white pine weevil to temperature and photoperiod with respect to the induction and termination of reproductive diapause.

Abstract: The nest-weaving spider mite Schizotetranychus miscanthi Saito showed a cline in male-to-male aggression intensity with minimum winter temperature. The altered kin structure in spring nests, which might be caused by winter harshness, was hypothesized to be a key factor responsible for the cline in male-to-male aggression. In Japan, we found two forms (high- and low-aggression forms) that showed different clinal trends with similar regression slopes and different intercepts. The former is characteristic of local populations from milder climates, whereas the latter occurs in harsher climates. We hypothesized that the intensity of female diapause, which may determine whether males are produced during late winter, was one of the factors separating these two clinal forms. In the four populations studied, short day length during the developmental period (egg to adult emergence) induced diapause in females. Diapause intensity varied greatly among populations, and particularly between the high-aggression and low-aggression forms. These data, together with data on winter harshness between the localities, led us to believe that female diapause is one of the factors affecting relatedness between interacting males in nests and can explain why the two forms of S. miscanthi have different clinal trends in male aggression in Japan.