The effect of implanted, active corpora allata on reproductive diapause in adult females of the grasshopper Oedipoda miniata

The effect of implanted active corpora allata (CA) on the reproductive diapause in adult females of the grasshopper, Oedipoda miniata, was investigated. Implantation of two pairs of CA originating from sexually mature, adult male Locusta migratoria migratorioides donors effectively terminated reproductive diapause by inducing oöcyte development and intensive egg-laying in O. miniata recipients at any state of the reproductive diapause. The interval elapsing from implantation till oviposition was 15 days when recipients were at the beginning of the reproductive diapause. This interval shortened when recipients were in later stages of the reproductive diapause, thus, closer to its eventual termination. Reproductive diapause in female O. miniata, therefore, seems to be a slow process rather than a steady state. In all instances recipients laid eggs for quite short periods (up to 3 weeks). After cessation of egg-laying resorption of the proximal oöcytes occurred in the ovarioles. The implanted glands presumably became inactive.Implantation of two pairs of CA originating from sexually mature (already in post-diapause state) male O. miniata donors also induced oöcyte development and occasional egg-laying in female recipients which were still in reproductive diapause at the time of implantation. The effect, however, was markedly less intensive than that induced by heterospecific implantation. Practically no oöcyte development was obtained in sham-operated and unoperated controls.

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Résumé L'implantation dans des femelles d'Oedipoda miniata en diapause génitale, de 2 paires de corpora allata (CA) prélevés sur des mâles adultes sexuellement mûrs de Locusta migratoria migratorioides, provoque la rupture de cette diapause, quel que soit son état d'évolution, en induisant le développement des ovocytes et une intense activité de ponte. La ponte est déclenchée dans un délai de 15 jours après l'implantation quand l'insecte receveur est en début de diapause génitale. Ce délai est plus court quand la diapause est déjà avancée, donc quand la greffe intervient à un moment plus proche de son achèvement normal. Par conséquent la diapause génitale chez la femelle d'Oedipoda miniata semble être un processus à évolution lente, plutôt qu'un état stable.Dans tous les cas les insectes ayant reçu un implant de CA pondent pendant une courte période (jusqu'à 3 semaines). Quand cesse la ponte la résorption des ovocytes proximaux survient dans les ovarioles; sans doute les glandes implantées sont devenues inactives.L'implantation de 2 paires de CA provenant de mâles d'Oedipoda miniata sexuellement mûrs (déjà dans un état de post-diapause) induit également le développement des ovocytes et occasionnellement la ponte chez des femelles en diapause génitale, mais l'effet est cependant nettement moins intense que celui induit par une greffe hétérospécifique. Pratiquement on n'observe aucun développement d'ovocytes chez les insectes témoins non-opérés ou ayant subi une pseudo-greffe.

     

Reversible reproductive diapause and intermediate states between diapause and full reproductive activity in male Oedipoda miniata grasshoppers

ABSTRACT. Previous publications have shown that aestival reproductive diapause is reversible in Oedipoda miniata (Pall.) males. Short days and/or relatively low temperatures terminate diapause, whereas long days and/or high temperatures maintain or reinduce it. The previous studies proved, however, only the effect of the temperature, or of the daylength—temperature combinations, and employed only male mating behaviour as an indicator of the state of diapause. The present work demonstrates that diapause can be maintained, terminated, or reinduced, solely by changes in the daylength. At a constant 27°C, diapause was terminated under LD 10.5:13.5, whereas it was maintained or reinduced under LD 18:6. The reproductive accessory glands were small in diapausing males and large in post-diapause ones, but their size decreased again with diapause reinduction, thus, they exhibited at least partially reversible changes. An intermediate state between full diapause and full reproductive activity was obtained under intermediate conditions of daylength and temperatures (LD 12:12; photophase (TP) at 38°C, scotophase (TS) at 27°C). In this state males showed consistently mild mating activity and intermediate size of the accessory glands, regardless of whether they had previously been in diapause or in post-diapause states. Under another combination of intermediate conditions (LD 16:8; TP = 26°C, TS = 13°C), another intermediate state with consistently little mating activity was observed. The 'all or none' principle does not apply to this diapause, rather the state of diapause may take any stable intermediate level between full diapause and full reproductive activity. The physiological and ecological implications of these findings are discussed.     

Repeated reversal of the reproductive diapause by photoperiod and temperature in males of the grasshopper, Oedipoda miniata

Short day-length and relatively low temperatures (LD 10.5 : 13.5, 26° during illumination, 13° during darkness) induced mating behaviour and terminated aestival reproductive diapause in males of the grasshopper Oedipoda miniata. Long days and high temperatures (LD 16 : 8, 38° during illumination, 27° during darkness) maintained sexual inactivity and diapause. Repeated changes of these conditions terminated, reinduced, reterminated and reinduced again diapause in the same males. An endogenous trend to complete diapause development and terminate diapause does not seem to exist in the males of this grasshopper; their reproductive diapause may be regarded as rather primitive.

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Résumé Les jours courts et les températures relativement basses (J/N; 10,30/13,30; 26°/13°) induisent le comportement sexuel et achièvent la diapause reproductrice estivale des mâles de l'Acridien Oedipoda miniata. Les jours longs et les températures élevées (J/N; 16/8; 38°/27°) inhibent l'activité sexuelle et provoquent la diapause.Des changements répétés de ces conditions achèvent, réinduisent, achèvent à nouveau et réinduisent à nouveau la diapause chez les mêmes mâles. Une tendance endogène pour achever le déroulement de la diapause et terminer la diapause ne semble pas exister chez les mâles de cette espèce, leur diapause reproductrice peut être considérée comme plutôt primitive.

     

The response of a homochrome grasshopper, Oedipoda miniata, to the dark-colour-inducing neurohormone (DCIN) of locusts

The effect of the dark-colour-inducing neurohormone (DCIN=[His(7)]-corazonin) of locusts was investigated in nymphs of the grasshopper, Oedipoda miniata, which exhibit strong homochromy, but neither green-brown, nor phase colour polymorphism. Graded doses of synthetic DCIN were injected in 1 μl of olive oil into 0-24-h-old penultimate nymphs. DCIN induced dose-dependent darkening in the recipients, seen 4 days after injection (still in the penultimate nymphal instar), as well as in the subsequent last-instar nymphs. The dose-range obtained between discernible and maximum (almost black) darkening extended over three orders of magnitude, from 1 pmol to 1 nmol of DCIN. In spite of the darkening observed already in the penultimate nymphal instar, the exuviae in the moult from this to the last nymphal instar did not show marked dark patches. However, the exuviae of the next moult (from last-instar nymph to adult) showed such dark patches, which increased with the increase of the dose, revealing the presence of exocuticular melanin. We conclude that DCIN, or a very close peptide, is the endogenous hormone which plays the major or sole role in the control of homochromy of O. miniata and possibly also of other acridids which exhibit homochromy.     

Age-dependent response of adults of a homochrome grasshopper, Oedipoda miniata, to the dark-colour-inducing neurohormone (DCIN) of locusts

Abstract The effect of the dark-colour-inducing neurohormone (DCIN = [His⁷]-corazonin) of locusts was investigated in field-collected young and old adults of the grasshopper, Oedipoda miniata (Pallas) (Orthoptera: Acrididae). This species shows homochromy, but neither green-brown, nor phase-dependent colour polymorphism. By injecting graded doses of synthetic DCIN in 2 µL of olive oil, young adults were tested within a week of their last moult, and old adults 3.5 months later, a few weeks before natural termination of their reproductive summer diapause. Colour changes were followed for 28 days after injection. Darkening of the young adults was considerable, but their response to DCIN is more moderate than that of conspecific nymphs, by exhibiting a higher threshold, slower response and weaker maximal response. Old adults also show a clear effect, but their response is even slower and less marked than the response of the young adults. It is concluded that the response to DCIN decreases from nymphs to young adults and it is further decreasing with ageing of the adults.     

Water balance and rectal absorption in the grasshopper Oedipoda

ABSTRACT. The xeric grasshopper Oedipoda germanica pyrenaica (Uvarov, 1936) has a daily cycle of water-gain from feeding during the afternoon and water-loss at night. The afternoon peak of water-gain in laboratory animals is correlated with a short-term rise in the osmotic pressure of the haemolymph in field animals. It is estimated that starved large animals would deplete their water reserves within 8–11 days. Water loss in faeces production is a major component of total water loss only during the late afternoon to early evening; at all other times transpiratory water losses are considerably greater. Overall, 23% of the daily water loss occurs through the faeces. From hindgut cannulation experiments, c. 80% of water entering the rectum is reabsorbed. A comparison of transpiratory water losses of xeric and mesic Orthoptera and some xeric Coleoptera revealed that water losses are some 6–7 times higher in Orthoptera than in similar sized Coleoptera.     

Reversible change in embryonic diapause intensity by mild temperature in the Chinese rice grasshopper, Oxya chinensis

The effects of temperature on maintenance and termination of embryonic diapause were investigated in Jining (35.4°N, 116.6°E) and Sihong (33.5°N, 118.2°E) strains of the Chinese rice grasshopper, Oxya chinensis Thunberg (Orthoptera: Catantopidae). Eggs of both strains entered diapause when incubated at 30, 25, or 20 °C. Chilling at 8 °C had an evident effect on diapause termination and almost all eggs chilled for 60 days ended diapause development. Chilling of eggs at 8 °C for only 20 days failed to result in any hatching at 20 °C, suggesting that such level of chilling was not enough to induce diapause termination. However, the treatment combining incubation of eggs at 30 °C for varying lengths of time with subsequent incubation to 20 °C had a distinct effect on the completion of diapause of the eggs. The results indicate that there were two temperature optima, that is, low temperature (chilling) and high temperature, for diapause development in this grasshopper species. Incubation of chilled eggs at 20 °C for 5–15 days followed by further incubation at 25 °C reduced termination of diapause significantly compared with the eggs only chilled at 8 °C. Exposure of eggs chilled at 8 °C to a pulse of 25 °C from 1 to 7 days, separated by a 20-day interval at 8 °C, resulted in a decrease in the percentage of successfully hatched eggs as the length of the pulse of 25 °C increased. The results suggest that diapause intensity may be restored at moderately high temperatures. This reversible change in diapause intensity would play an important role in maintaining diapause before winter.     

Melatonin synthesis in the optic lobes and midbrain of the grasshopper Oedipoda caerulescens

The pathways of insect melatonin (MEL) biosynthesis apparently follow the same routes as those identified in vertebrates but information on MEL synthesis variations related with serotonin (5‐HT), 5‐hydroxy‐indole acetic acid (5HIAA), and N‐acetylserotonin (NAS) levels, as well as 5‐HT N‐acetyltransferase (NAT) activity throughout the day, is very limited in the insect nervous system. In the present study, the levels of MEL, metabolites (5‐HT, NAS, and 5‐HIAA) and enzyme NAT were determined in the optic lobes and the midbrain of the grasshopper Oedipoda caerulescens, in conditions of light and darkness. In both tissues, a different pattern of MEL synthesis was observed over the light/dark cycle. Variations in the levels of 5‐HT, NAS and NAT activity related to the synthesis of cerebral MEL follow a pattern very similar to that observed in the pineal of mammals, with a peak of synthesis in the first half of the scotophase. Also, we observed differences in the metabolism of 5‐HT between the optic lobes and the midbrain light/dark‐dependent.     

Metapopulation dynamics in a regional population of the blue-winged grasshopper (Oedipoda caerulescens; Linnaeus, 1758)

For two consecutive years we registered the presence (or absence) of blue winged grasshoppers (Oedipoda caerulescens; Linnaeus, 1758) on 312 habitat patches of differing size in a region of more than 3000 ha. The data show that presence of grasshoppers on a habitat patch is dependent on patch size as well as on patch isolation. We used an ecological incidence model to describe the metapopulation dynamics of the regional population and derived the parameters for this model from presence-absence data and observations of Oedipoda dispersion. The analysis shows that local extinction of grasshopper populations is influenced by strong fluctuations of environmental conditions and that for a number of small patches in our region recolonization is important for the presence of O. caerulescens. Colonization probability, as derived using the incidence model, is in good agreement with estimates from a population genetical analysis.     

Termination of diapause in the Cinnabar moth (Tyria jacobaeae) by chilling

The effect of chilling time on the termination of pupal diapause was studied in the Cinnabar moth, Tyria jacobaeae L., Lepidoptera: Arctiidae. Chilling followed by a temperature of 20°C was effective in terminating diapause. Chilling for 120 days immediately after pupation yielded the highest percentage emergence and resulted in the shortest total pupal development time (162 days). A more natural treatment, a warm period before cold treatment, did not result in a higher percentage of emergence or in a shorter total pupal development time.During hibernation this species experiences two successive processes: diapause development during the first three to four months of cold, followed by a period of quiescence. Application of high temperatures in this latter period immediately starts morphogenesis. The impact of a relative humidity of 70% during the pupal stage for complete wing unfolding is demonstrated. The underlying mechanism of diapause is discussed.

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Résumé L'effet sur la levée de la diapause de différents régimes de température infligés aux chrysalides est étudié chez Tyria jacobaeae L. (Lepidoptera: Arctiidae). Une mise au froid suivie de hautes températures lève efficacement la diapause. Un refroidissement pendant 120 jours immédiatement après la nymphose entraîne le plus grand pourcentage d'éclosions et la durée totale du développement des chrysalides la plus courte (162.3 j). Un traitement plus naturel, une période chaude avant la période froide, n'entraîne pas un plus grand pourcentage d'éclosions ni une durée plus courte de développement.Il est proposé que durant l'hibernation cette espèce passe par deux processus successifs: un diapause durant les premiers trois ou quatre mois de froid, suivie d'une période de quiescence. Le transfert à des hautes températures pendant cette derpériode déclanche immédiatement la morphogénèse. L'influence d'un taux élevé d'humidité relative durant le stade chrysalide sur le déploiement complet des ailes est démontré. Le méchanisme de diapause sous-jacent est discuté.

     

中华稻蝗的胚胎发育及卵滞育发生的胚胎发育阶段

为弄清中华稻蝗Oxya chinensis(Thunberg)卵滞育发生的胚胎发育阶段,观察了其胚胎发育过程,检测了中华稻蝗铁岭、济南、长沙及儋州种群产卵后卵粒含水量的变化规律和胚胎发育的停滞时期.根据胚胎形态,自原头与原颚胸折叠的胚胎发育阶段开始,将中华稻蝗的胚胎发育过程划分为11个阶段.在25℃的温度条件下,4个地...     

Female receptivity, embryonic diapause, and superfetation in the European badger (Meles meles): implications for the reproductive tactics of males and females

The European badger Meles meles is thought to mate throughout the year with two mating peaks occurring in late winter/spring and summer/autumn. After mating, fertilized ova enter embryonic diapause (delayed implantation) at the blastocyst stage, which lasts up to eleven months. Even if mating is successful, however, the estrous cycle may continue during embryonic diapause, which suggests that female badgers are capable of superfetation (conception during pregnancy). This may increase female fitness by facilitating polyandry, and reduce the risk of infanticide by resident males through paternity confusion. Detailed understanding of female receptivity, specifically the association of superfetation with embryonic diapause, may explain field observations of seemingly inconsistent reproductive tactics of male badgers with regard to, for instance, whether or not they guard mates or defend territories. The combination of embryonic diapause and superfetation may occur in other mustelids; if so, the sociobiology of mustelids will need reevaluating, and the Mustelidae may prove to be a good model taxon for studies of sexual conflict in the reproduction of eutherian mammals.     

Population density, phenotype and reproductive output in the grasshopper Chorthippus brunneus

ABSTRACT. 1. The effects of population density on the reproductive output of individual female grasshoppers ( Chorthippus brunneus Thunberg) and the relationships between reproductive output and component elements of each female's phenotype, were investigated.
2. Reproductive output was primarily determined by the rate of egg-pod production. Increased density led to significant reductions in the rate of egg-pod production and reproductive output.
3. Exoskeleton size (reflecting nymphal experience) was positively correlated with clutch size at both high and low densities, but condition (reflecting adult experience) showed no such correlation. At high density, exoskeleton size was more strongly correlated with the rate of egg-pod production and reproductive output than condition. It is concluded that the nymphal aspects of size are more important than the adult aspects.
4. At low density, females with small exoskeletons compensated for their smaller clutches by producing egg-pods at a faster rate. Thus, there was no overall relationship between reproductive output and any of the phenotypic characteristics.
5. The effects of competition were weakly asymmetric in high density populations. The weakness of the asymmetry suggests scramble-like interactions for resources. It is concluded that not only are the effects of competition influenced by individual differences, but also that competition may reveal differences that would not otherwise be apparent.     

Termination of pupal diapause in the pine processionary moth Thaumetopoea pityocampa

Diapause development is a complex process involving several eco‐physiological phases. Understanding these phases, especially diapause termination, is vital for interpreting the life history of many insect species and for developing suitable predictive models of population dynamics. The pine processionary moth is a major defoliator of pine and a vertebrate health hazard in the Mediterranean region. This species can display either univoltine or semivoltine development, with a pupal diapause extending from a few months to several years, respectively. Although the ecological and applied importance of diapause is acknowledged, its physiological regulation in either case remains obscure. In the present study, we characterize pre‐termination, termination and post‐termination phases of pupae developing as univoltine or remaining in prolonged diapause. Changes in metabolic activity are monitored continuously using thermocouples, comprising a novel method based on direct calorimetry, and periodically by use of O₂ respirometry. The two methods clearly detect diapause termination in both types of pupae before any visible morphological or behavioural changes can be observed. Univoltine individuals are characterized by an increase in metabolic activity from pre‐termination through to termination and post‐termination, ultimately resulting in emergence. Remarkably, a synchronous termination is observed in individuals that enter prolonged diapause instead of emerging; however, in these pupae, the increased metabolic activity is only transient. The present study represents a starting point toward understanding the eco‐physiology of diapause development processes in the pupae of the pine processionary moth.     

Termination and induction of diapause in the gypsy moth larval parasitoid, Apanteles melanoscelus

Diapause in Apanteles melanoscelus can be terminated by exposure of the diapausing last instar larvae within their cocoons to 5°C for a period of 8 or more weeks. Photoperiod has no consistent influence upon diapause termination, but is of paramount importance for diapause induction. At less than 16 hr light per day virtually all larvae diapause, and at 18 hr and above very few larvae diapause. By exposing different larval stages to different photoperiods it was found that older larvae were most sensitive to the light-dark cycle. It was also noted that cocoons of diapausing larvae are larger than those of non-diapausing larvae.     

Effects of photoperiod, temperature, and host plant age on induction of reproductive diapause and development time in Danaus plexippus

Abstract 1. Diapause induction in monarch butterflies Danaus plexippus was studied using adults captured from the wild in Minnesota and Wisconsin, and individuals reared under outdoor and controlled conditions.
2. Oocyte presence in females and ejaculatory duct mass in males were used to indicate reproductive status.
3. Some wild individuals were in diapause in mid-August, and all males and females were in diapause by late August and early September respectively.
4. Individuals reared under decreasing day lengths and fluctuating temperatures were more likely to be in diapause than were individuals reared under long or short day lengths or constant temperatures.
5. Individuals fed potted old Asclepias curassavica plants were more likely to be in diapause than were those fed potted young host plants; when cuttings of Asclepias syriaca plants from the field or greenhouse pots were used, there was no effect of host plant age.
6. Extremely high temperatures increased the number of day-degrees required for development from egg to adult, while decreasing day lengths and older host plants tended to decrease the number of day-degrees required for development.
7. There appears to be a continuum of reproductive development in monarchs, with gradual declines in mean ejaculatory duct mass and oocyte production during the late summer.
8. None of the experimental treatments led to 100% diapause, and diapause was more likely to occur in monarchs subjected to more than one diapause-inducing cue.     

Induction of adult diapause and of low and high reproductive states in a parasitoid wasp,Ooencyrtus nezarae, by photoperiod and temperature

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) was reared on eggs ofRiptortus clavatus (Thunberg) (Heteroptera: Alydidae) at various temperatures under long-day (L16:D8) or short-day (L10:D14) conditions. There was no diapause during egg, larval or pupal stages under any set of conditions examined. However, at 15°C under short-day conditions, vitellogenesis was arrested in all adult females and they entered diapause. At 15°C under long-day conditions, or at 20°C under short-day conditions, some adult females entered diapause. Under the latter set of conditions, the adult females laid eggs but they laid fewer eggs than under long-day conditions, Even at 25°C, under short-day conditions, adult females laid fewer eggs than under long-day conditions, and this low rate of oviposition was attributed to the retarded development of ovaries. Diapause adults reared at 15°C were more resistant to low temperature than nondiapause adults reared at 25°C.