Abstract: The timing of springtime production of diapausing eggs by a population of the freshwater copepod, Diaptomus sanguineus, has been shown previously to be consistent with avoidance of seasonally intense fish predation. Natural selection acting on the timing of diapause fluctuates between years depending upon the population density of fish. Here we show that, in the field, the mean timing of diapause shifts between years in response to fluctuations in selection. Diapause is earlier in years following high predator density, and is later in years following low predator density. Although selection intensity in individual years may be large, the mean intensity over the decade of fluctuating selection investigated here is close to zero. Photoperiod sensitivity of the diapausetiming trait is heritable in the laboratory. The combination of fluctuating selection and multi-generation storage of genotypes as diapausing eggs in lake sediments may contribute to the maintenance of the genetic variation that permits the rapid selection response seen in the field.

Abstract: Females of a wild-type strain of Drosophila melanogaster (Canton-S), and of several clock mutants (period), were able to discriminate between diapause-inducing short days and diapause- averting lon...

Abstract: The 1st feature revealed typical for diapause phenomena inTrichogramma species is the interaction of environmental conditions in both parental and filial generations in induction of diapause in the latter. Lowered temperature during larval development is the ultimate factor evoking diapause in pronymphs but the norm of this thermal reaction is not fixed but varies depending on photoperiod and temperature in the previous generation due to maternal influence. Short day and in some cases high temperature in parental generation enhance tendency to diapause in the progeny. Unlike maternal influence the development to filial generation itself is not (or almost is not) governed by its own photoperiodic reaction. The 2nd typical feature revealed is the occurrence of endogenous process running in the sequence of generations and causing changes in the diapause tendency and underlying reaction norms even under constant rearing conditions.

Abstract: The freshwater calanoid copepod Diaptomus sanguineus switches each year in spring from making eggs that hatch immediately to making diapausing eggs that rest in lake sediments for an extended period. In lakes and ponds containing planktivorous fish, the timing of the switch is highly consistent between years and comes at the theoretically optimal time (late March) to avoid intense summer predation. In fishless ponds the timing comes 1—2 mo later. We investigate here the environmental cues used by the copepods to time the switch to diapause. Through the use of both field and laboratory manipulations, we show that temperature and photoperiod play central roles as diapause stimuli. A field manipulation of fish density failed to reveal either a direct induction of diapause or any more subtle effects of fish occurrence on diapause timing. The copepods made immediately hatching eggs under short—day or low—temperature conditions, and diapausing eggs under long days or high temperatures. There appears to be variation between individuals in their responses to temperature and photoperiod so that similar diapause phenologies are produced by different sensitivities to the environmental cues.

Abstract: Transmission electron microscope studies on the morphology of subitaneous and diapause eggs in the neustonic copepodPontella mediterranea, collected in coastal waters of the Gulf of Naples from May to December 1986, revealed striking structural differences between the two egg types and the existence of a third egg type that was morphologically similar to a diapause egg but which hatched within 2 to 3 d. In smooth, subitaneous eggs the plasma membrane was surrounded by a thin outer chorion as compared to the thick and highly complex four-layer structure enveloping subitaneous eggs with short spines, and diapause eggs. This coat may be assembled just prior to or after deposition since the morphology of developing oocytes was similar in females laying either subitaneous or diapause eggs. The only other major structural difference between the two egg types was the presence of numerous, disc-like bodies in the ooplasm of diapause eggs. Development was arrested for at least 3 mo, prior to the initiation of the first cleavage, suggesting that these eggs were kept dormant by some endogenous and, possibly, structural mechanism preceeding the termination of diapause.

Abstract: Diapause eggs of the silkworm, Bombyx mori, exposed to 5°C and 0.5°C from 2 or 30 days after oviposition, were examined for changes in contents of glycogen, sorbitol and glycerol. Cold acclimation did not alter the profile of accumulation of sorbitol from that in eggs kept continuously at 25°C. However, acclimation at 5°C resulted in conversion of sorbitol to glycogen, while acclimation at 0.5°C was not accompanied by the utilization of sorbitol. NAD-sorbitol dehydrogenase (NAD-SDH; EC 1.1.1.14) activity was examined in the cold-acclimated eggs. The activity was induced by acclimation at 5°C but not at 0.5°C. Incubation at 0.5°C suppressed any further increase in the activity that had been induced. Temperature-directed changes in NAD-SDH activity paralleled those in sorbitol content. Hatching of the diapause eggs was monitored after cold acclimation for various periods of time and subsequent transfer to 25°C. Incubation at 0.5°C was less effective than 5°C at breaking diapause. The time required for the eggs to hatch in synchrony after acclimation at 5°C coincided with that required for the induction of NAD-SDH activity. These results show that different effects result from acclimation at 5°C and near 0°C with respect to the control of NAD-SDH activity, that utilization of sorbitol is controlled by NAD-SDH activity, and that induction of this activity is temperature-dependent. Furthermore, induction of NAD-SDH activity is involved in the termination of diapause in B. mori.

Abstract: That analogs or mimics of insect juvenile hormones could be used to control insects by disrupting their diapause, thus uncoupling the target insects from the seasonal cycles of their environment, was once considered a promising possibility for insect management. The animals would die during an inimical period because survival mechanisms are lacking. However, laboratory studies revealed no promising model system and the concept languished. I found that the reproductive diapause of pear psylla, Cacopsylla pyricola (Foerster) (Homoptera: Psyllidae), was terminated by topical application of as little as 1 ng per insect of fenoxycarb, a carbamate that mimics juvenile hormone. Seasonally inappropriate ovarian development and mating began when fenoxycarb was applied to the foliage upon which adults fed and rested. The same effect was shown in field tests. Disruption of diapause with juvenoids may still be a viable strategy for insect pest management.

Abstract: Mating activity of pear psylla, Cacopsylla pyricola (Foerster), with emphasis on the morphologically distinctive overwintering winterform generation, was characterized in the laboratory Generally, one spermatophore was passed per copulation Presence of light, size of the mating arena, and the number of leaves in the arena affected mating frequency; the highest mean frequency observed was 918 matings per 24 h Diapausing psylla males, after being conditioned under long photoperiod (16:8 [L:D]), mated significantly more often than those conditioned under a photoperiod of 12:12 or 10:14 (L:D) The photoperiodic experience of the female did not affect mating frequency Visual observation of behavior revealed that the winterform males conditioned under short days made as many sexual advances as winterform males conditioned under long days, but diapause males were rejected by the females Pairings of winterform females with summerform males had significantly fewer inseminations compared with pairings involving the same seasonal forms; there is a behavioral barrier to mating between the generations

Abstract: During the last-larval instar, Ostrinia may display a facultative larval diapause. Diapausing larvae contain very low ecdysteroid titers and exhibit poorly differentiated imaginal wing discs. After diapause, development resumes when larvae are placed in favorable post-diapause conditions. After a few days in these conditions, a small and transient peak of 20-hydroxyecdysone was observed in hemolymph before any visible resumption of imaginal wing disc development. [3H]Cholesterol-labeling experiment confirmed this result. Conversion of [3H]Cholesterol into [3H]ecdysteroids also began before any visible resumption of wing disc development. These data suggest that the resumption of wing disc development is induced by very low concentrations of molting hormone. After this small first peak, ecdysteroid concentrations increase until a second peak, which precedes ecdysis. Increase of titers was correlated with an increase of biosynthetic activity from [3H]cholesterol. Unexpectedly, biosynthetic activity remained very high after the second peak, but the synthesized ecdysone was immediately inactivated into 20-hydroxyecdysonic acid.

Abstract: Dormancy in the gypsy moth is a dynamic process characterized by complex and seasonally variable responses to physical factors. At the end of summer and the beginning of autumn, short daylengths play a small, but perceptible role in diapause maintenance in a small proportion of individuals. By comparison, temperature has a much larger role in diapause maintenance and in the timing of postdiapause hatching. Temperatures >;15.6°C decelerate diapause development, and thus maintain diapause, whereas exposure to 5.0 or 10.0°C accelerates diapause development and enhances the incidence, speed, and synchrony of hatching under warm conditions. A small proportion of individuals in some egg masses need not experience low temperature before they hatch; these individuals hatch in the fall. The thermal responses of the larvae within the eggs change as they undergo dormancy in nature; these changes are evident in the temperature-developmental response curves, the lower thermal thresholds and heat units required for hatching, and the relative rates of development under a range of temperatures. The pattern of change in the thermal responses throughout dormancy suggests that as autumn and winter proceed, there is a gradual transition from diapause to postdiapause periods of dormancy. Thermal responses during dormancy vary considerably among egg masses.

Abstract: The post-embryonic development of Pieris brassicae can either be continuous (under a long photoperiod) or interrupted at the pupal stage (induced by a short photoperiod); this phenomenon is termed facultative diapause. Several studies have indicated that certain brain mechanisms could be directly involved in the perception of variations in the photoperiod and could mediate some physiological effects particular to dormancy. Biogenic amines have been particularly implicated in the response to photoperiod variations and also in the regulation of development, especially in diapause induction and termination. High performance liquid chromatography with dual electrochemical detection has therefore been used to measure several biogenic amines in pupal nervous tissues at various stages of nondiapausing and diapausing development. During direct development, the levels of dopamine (DA) and N-acetyldopamine (NADA: a DA metabolite) in brain were relatively high in 3-day-old pupae and at the end of pupal life (on the 8th day). Dihydroxyphenylacetic acid (another metabolite of DA) showed no variation. Serotonin was mainly observed in 2–3-day-old pupae but 5-hydroxyindoleacetic acid was never detected. In young diapausing insects, similar variations of DA levels were observed even though a slight decrease of DA metabolites was noted. Serotonin appeared somewhat later (4–5 days) and attained higher levels. In late diapausing pupae, a marked increase in DA levels was observed, especially when pupae were kept at low temperature (4°C). During diapause, serotonin levels were reduced or even absent.

Abstract: 1. 1. The activity of NAD-sorbitol dehydrogenase (NAD-SDH; EC 1.1.1.14) and levels of sorbitol were examined in non-diapause eggs of the silkworm, Bombyx mori, exposed to temperatures of 20-0.5°C from 1 day after oviposition. The morphology of embryos in the cold-acclimated eggs and the hatching of eggs after transfer to 25°C were monitored. 2. 2. Temperatures between 15 and 0.5°C retarded the development of NAD-SDH activity at a specific embryonic stage that was comparable to diapause, and sorbitol accumulated in the eggs. 3. 3. With the appearance of NAD-SDH activity, sorbitol was converted into glycogen, just as it is in diapause eggs. The results indicate that NAD-SDH participates in the utilization of sorbitol rather than in its formation in non-diapause eggs. 4. 4. Distinct effects of low temperatures on the morphological development of the embryos are also discussed.

Abstract: Flight ability has undoubtedly been an important contributing factor for the large success of insects as a group. Although some insects may travel considerable distances by means other than flight, flight is nevertheless by far the most common means for insects to move to new habitats. Migratory flights, by which insects move to new habitats for breeding or diapause, are performed during a limited period in adult life. During this period the insect is behaviourally and physiologically committed to flight, whereas other functions such as feeding and reproduction tend to be suppressed (Johnson 1969, 1976; Rankin 1985; Kennedy 1985).

Abstract: Eurydema rugosa Motschulsky (Heteroptera: Pentatomidae) entered adult diapause under a short-day photoperiod, whether the food was leaves or seeds of Brassica napus L. Under a long-day photoperiod, adults raised on leaves became reproductive. However, adults raised on seeds entered diapause even under a long-day photoperiod, although they were nutritionally better than leaves in respect of mortality and weight gain in the nymphal period. It is suggested that E. rugosa uses the status of the host plant as a cue for timing the diapause induction. Resume Induction de la diapause d'Eurydema rugosa par la consommation de graines E. rugosa Motschulsky (Heterop. Pentatomidae) entre en diapause imaginale en jours courts, lorsqu'il s'alimente avec des feuilles ou des graines de Brassica napus L. En jours longs, les adultes eleves sur feuilles se reproduisent; par contre, eleves sur graines, ils entrent en diapause, bien que leur alimentation ait ete meilleure que sur feuilles a en juger par la mortalite et le gain de poids pendant le dernier stade larvaire. On suggere que E. rugosa utilise l'etat de la plante hote comme moyen de regler l'induction de la diapause.

Abstract: The effect of a juvenile hormone mimetic, fenoxycarb, Ro 13-5223, was tested on the larval instars of the European corn borer,Ostrinia nubilalis, by dipping or topical application. When larvae were treated in instars 2, 3 or 4, the duration of the fifth instar was modified. More permanent and fewer supernumerary larvae were obtained when treatment occurred in the early instars. This non-neurotoxic compound exhibited a strong dose-dependent juvenile hormone type of activity when it was applied to last instar larvae. Fenoxycarb prevented the onset of pupation and produced supernumerary larvae and intermediates. Permanent larvae were obtained if fenoxycarb was applied on day 0 or day 1 of the last instar. The use of such a JH mimetic in the understanding of endocrine control of diapause is discussed.

Abstract: The facultative diapause of Ascogaster quadridentata depends upon the photoperiod experienced by its host. A host exposed to short day lengths (12L:12D) ceases development in its fourth stadium, spins a cocoon, and remains dormant throughout the winter. A first stadium parasitoid larva overwinters in a true diapause, within its dormant host. Dormancy of both animals is due to a failure of the host's endocrine system. Upon transfer of the host from dormancy-maintaining (OL:24D, 4°C) to dormancy-terminating conditions (DTC = 16L:8D, 25°C) a host cephalic factor is released. The cephalic factor blocked by host ligation within 48 h of transfer to DTC was circumvented by an injection of the host with 20-hydroxyecdysone. Parasitoid larvae that were either isolated within the abdomen of 20-hydroxyecdysone-injected hosts or held in vitro with the molting hormone initiated apolysis. An increased titer of hemolymph juvenile hormone, which was present 48 h after the host was transferred to DTC, may have had a prothoracicotropic effect upon the host/parasitoid unit. A topical application of 1 ng of methoprene, concurrent to host transfer to DTC, accelerated parasitoid development. No parasitoid development was evident if the host was neck-ligated at the time of its methoprene treatment and transfer to DTC. These data suggest that the prothoracicotropic effect of methoprene was via the host head, rather than directly on the host prothoracic glands, or the parasitoid itself.

Abstract: Catops nigricans reproduces in the autumn. Pre-imaginal development is temperature-dependent and takes place during the winter, followed by aestivation in the early adult stage. This summer diapause is obligatory and temperature independent. It synchronizes the monovoltine life cycle with the annual cycle. In three populations collected near Kiel (54°22′ N, 10°6′ E), Koln (50°54′ N, 7°6′ E), and Paris (49°25′ N, 2°20′ E), pre-imaginal development slowed and the duration of summer diapause decreased with increasing latitude. Synchronization of the critical breeding interval with the appropriate environmental conditions was achieved through temperature- and photoperiod-dependent sensitivity of ovipositing adults, through different thermal thresholds in eggs, larvae, and pupae, and through sensitivity to photoperiod in third-instars larvae.C. nigricans copes with the unpredictability of climatic conditions in different ways. The local populations have evolved a mean diapause length which probably adjusts the life cycle in most years to the optimal date for reproduction. The mean diapause length was 77 days for Kiel, 98 days for Koln and 138 days for Paris at 10°C, short-day (=SD).C. nigricans also spreads the risk by varying diapause length. Amongthe progeny of single females the range of diapause duration covered about 70% of the total range of the whole population. The oviposition rate of females confined to subterranean life was the same as females confined to subterranean life was the same as in those living under the influence of a varying photoperiod.C. nigricans should therefore be able to live both in the litter layer of forests and also in the nests and galleries of small mammals.

Abstract: Most Bruchidae (Coleoptera) are specialists developing on a limited number of species of Leguminosae. Host selection is by females ovipositing on pods which usually are available only during a short period of the year. Thus, there is a precise synchronization between the reproductive cycles of the plants and bruchids. Experiments in the field and laboratory show that Bruchidius atrolineatus (Pic) and Bruchus rufimanus (Boh.) are in reproductive diapause when the pods of their host plant are absent. The appearance of flowers induces diapause termination and make insects sexually active at the beginning of the fructification period. Chemicals produced by flowers probably stimulate the development of oogenesis. Chemical or tactile stimuli perceived in direct contact with the pods stimulate oviposition on the trophic substratum of the larvae. These interactions increase the reproductive fitness of the insects and explain the high levels of bruchid infestations, particularly in crops. Some structures observed in wild Leguminosae could represent defenses against bruchids. The texture of the pods could modify egg-laying behaviour; the size, the structure and the chemical composition of the seeds could influence larval development. The importance of these host plant characteristics is analyzed in relation with the hypothesis of coevolution.

Abstract: Cricket life-cycles can be classified into two major types, homodynamic and heterodynamic (Masaki and Walker 1987). In the homodynamic type, growth and reproduction continue at similar rates or under similar thermal control (Q 10 = 2 to 3) throughout the year, while in the heterodynamic type they are retarded by the intervention of diapause and/or the response to seasonal cues such as photoperiod (Masaki 1978; Tanaka 1983, 1984). Since the life-cycles of extinct forms cannot be reconstructed from fossils, there is no direct means of knowing which one, homodynamic or heterodynamic, is the ancestral type. Only circumstantial evidence suggests that the homodynamic is ancestral.