Endocrine changes associated with metamorphosis and diapause induction in the yellow-spotted longicorn beetle, Psacothea hilaris

At 25 degrees C and under a long-day photoperiod, all 5th instar Psacothea hilaris larvae pupate at the next molt. Under a short-day photoperiod, in contrast, they undergo one or two additional larval molts and enter diapause; the 7th instar larvae enter diapause without further molt. The changes in hemolymph juvenile hormone (JH III) titers, JH esterase activity, and ecdysteroid titers in pupation-destined, pre-diapause, and diapause-destined larvae were examined. JH titers of the 5th instar pupation-destined larvae decreased continuously from 1.3 ng/ml and became virtually undetectable on day 13, when JH esterase activity peaked. Ecdysteroids exhibited a small peak on day 8, 1 day before gut purge, and a large peak on day 11, 2 days before the larvae became pre-pupae. The two ecdysteroid peaks are suggested to be associated with pupal commitment and pupation, respectively. JH titers of the 5th instar pre-diapause larvae were maintained at approximately 1.5 ng/ml for 5 days and then increased to form a peak (3.3 ng/ml) on day 11. JH esterase activity remained at a low level throughout. Ecdysteroid levels exhibited a large peak of 40 ng/ml on day 18, coincident with the larval molt to the 6th instar. JH titers of the 7th instar diapause-destined larvae peaked at 1.9 ng/ml on day 3, and a level of approximately 1.1 ng/ml was maintained even 30-60 days into the instar, when they were in diapause. Ecdysteroid titers remained approximately 0.02 ng/ml. Diapause induction in this species was suggested to be a consequence of high JH and low ecdysteroid titers.     

Relationship between an increase of juvenile hormone titer in early instars and the induction of diapause in fully grown larvae of Sesamia nonagrioides

The larvae of Sesamia nonagrioides (Lepidoptera: Noctuidae) grown at 25 degrees C and long photoperiod (16:8h light:dark) pupate in the 5th or 6th (mostly) larval instar, while the larvae reared under a short photoperiod (12:12h) enter diapause during which they consume some food and undergo up to 12 (usually 3-4) stationary larval molts. Diapause programming includes an increase of juvenile hormone (JH) titer in the hemolymph from about 20 to 50 nM in the 4th and 5th instar larvae (titer in earlier instars was not measured). JH I, II, and III are present in approximate ratio 1-2:10:1. The JH titer drops to zero before pupation but remains around 20 nM during diapause. Perfect extra larval molts associated with a body weight increase can be induced in the non-diapausing larvae with a JH analogue (JHA). The weight rise is due to accumulation of reserves and not to a general body growth. The timing of extra molts is similar to the molting pattern of the diapausing larvae only when JHA is present since early larval instars. In the diapausing larvae, JHA application affects neither molting periodicity nor the body weight. It is concluded that (1) Increased JH titer in early larval instars is a part of diapause programming; (2) The extension of larval stage in the diapausing larvae, but not the timing pattern of extra molts, is due to continuously high JH titer; (3) The diapause program includes low food intake, maintenance of a certain body weight, and periodic larval molts.     

The role of juvenile hormone in the larval diapause of the European corn borer,Ostrinia nubilalis

The possible role of juvenile hormone (JH) in the induction and termination of larval diapause in the European corn borer, Ostrinia nubilalis, was investigated using topical applications of both JH I and a JH mimic as well as by monitoring JH titers with the Galleria bioassay. Neither JH nor the JH mimic ZR515 was capable of influencing diapause termination when administered topically. The Galleria bioassay revealed little or no JH in the hemolymph of mid diapause (>30 days) insects, indicating no demonstrable role for JH in diapause maintenance. When ZR515 was administered to nondiapause, newly ecdysed fifth instar larvae the pupal molting cycle was delayed. By use of photoperiodic regimes we were able to show that the molting delay was not equivalent to diapause induction. The Galleria bioassay showed differences in JH titer profiles between diapause and nondiapause animals during the final larval stadium. The nondiapause insects showed titers that decline rapidly to trace amounts following the molt to fifth instar then rose prior to pupation. The diapause insects had generally higher titers and exhibited a more gradual decline after the molt. No evidence was obtained to support the hypothesis that JH plays a key role in the induction, maintenance, or termination of larval diapause.     

Juvenile hormone esterase activity in the pupating and diapausing larvae of Sesamia nonagrioides

The development of the Mediterranean corn borer, Sesamia nonagrioides, under long-day (LD) photoperiod is associated with juvenile hormone (JH) decline and pupation in the 5th or 6th larval instar. The larvae grown under short-day (SD) conditions maintain a moderate JH titer and enter diapause during which they undergo several extra larval molts. Both types of larvae exhibit similar levels of juvenile hormone esterase (JHE) activity that increases in each instar during the period of low ecdysteroid titer and drops when the titer rises to a molt-inducing peak. A suppression of JHE activity within 24h after application of an ecdysteroid agonist suggests that the drop of activity is a rapid and possibly direct response to ecdysteroids or their agonist. Esterase inhibitor 3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) suppressed more than 98% of the JHE activity without affecting pupation timing and adult development. The data indicate that JHE is not crucial for the switch between larval development, diapause, and metamorphosis in S. nonagrioides.     

Reproductive and developmental consequences of a diapause maternal effect in the flesh fly, Sarcophaga bullata

Abstract Progeny of Sarcophaga bullata produced from mothers with a history of short day will not enter pupal diapause even if they are reared in a strong diapause-inducing environment (LD 12:12 h at 20^oC). Short-day exposure and diapause commitment are normally inseparable, but this maternal effect provides a tool for examining separately the effect of photoperiod and diapause commitment. Duration of the wandering period of the third instar is longer in diapause-destined larvae than in non-diapause-destined larvae, and fecundity of flies that have experienced pupal diapause is lower than in long-day flies that have not been through diapause. The puparia of diapausing pupae contain more hydrocarbons than puparia of nondiapausing pupae, and this contributes to higher rates of net transpiration for the nondiapausing flies. Flies showing the maternal effect (short-day experience but no diapause) show an intermediate response: length of wandering, fecundity rate and quantities of puparial hydrocarbon are between the extremes observed in the other two groups of flies. Thus, the maternal effect switches the developmental programme to nondiapause, but the progeny retain some characteristics of diapause. Evidence from reciprocal crosses indicates that the photoperiodic history of the female, rather than the male, is responsible for the influence on fecundity.     

Endocrine interactions controlling the larval diapause of the southwestern corn borer, Diatraea grandiosella

The effect of hormone treatments on larvae of the southwestern corn borer, Diatraea grandiosella, was examined to explore endocrine interactions which regulate its mature larval diapause. This species is especially suitable for investigating the endocrine control of larval diapause because it ecdyses from a spotted to an immaculate morph at the onset of diapause, and the immaculate morph may undergo up to three stationary ecdyses during diapause. The response of prediapause larvae to a β-ecdysone injection showed that the larvae have the potential to transform into the immaculate morph early in the final larval instar, but under normal conditions this ecdysis occurs after larvae reach maturity. Since a high rate of pupation occurred among early diapause larvae which received a head ligature, followed 17 days later by a β-ecdysone injection, diapause larvae retain active corpora allata. Since a head ligature prevented diapause larvae from responding to repeated topical applications of a juvenile hormone (JH) mimic or JH 1, the intermediate titer of JH associated with larval diapause may inhibit the synthesis or transport of ecdysiotropin, or its release from the corpora cardiaca. Current results suggest, therefore, that an interaction between the cerebral neurosecretory system and the corpora allata regulates the initiation, maintenance, and termination of this larval diapause.     

A Role for Ecdysteroids in the Induction and Maintenance of the Pharate First Instar Diapause of the Gypsy Moth,Lymantria dispar

Several lines of evidence suggest a novel regulatory mechanism for diapause regulation in the gypsy moth. We propose that ecdysteroids play a role in the induction and maintenance of the pharate first instar larval diapause in this species. A 55 kDa gut protein that is indicative of diapause is expressed in intact and neck-ligated pharate larvae but is not expressed when a ligature is placed posterior to the prothorax, site of the prothoracic gland. Guts cultured in vitro for 12 h cease to synthesize the 55 kDa protein, but synthesis of the protein resumes if the culture medium is enriched with a prothorax extract from pharate larvae or a prothoracic gland extract from fifth instar larvae. Injection of 20-hydroxyecdysone or the ecdysteroid agonist, RH-5992, into isolated abdomens stimulates synthesis of the diapause-specific 55 kDa protein, suggesting that the essential factor from the prothorax is an ecdysteroid. KK-42, an imidazole derivative known to inhibit ecdysteroid biosynthesis, averts diapause when applied to prediapausing pharate first instar larvae, but this effect can be countered by application of 20-hydroxyecdysone or RH-5992, i.e. KK-42 treated pharate larvae that are exposed to an ecdysteroid or RH-5992 readily enter diapause. A chilling period (120 days at 5 degrees C) is normally adequate to prompt an immediate termination of diapause when pharate larvae are transferred to 25 degrees C, but if such larvae are held in hanging drop cultures with ecdysteroids they fail to terminate diapause. Together, these results suggest that ecdysteroids are essential for the induction and maintenance of diapause and imply that a drop in the ecdysteroid titer is essential for diapause termination. Copyright 1997 Elsevier Science Ltd. All rights reserved     

滞育和非滞育棉铃虫血淋巴类固醇蜕皮素含量变化的比较

采用放射免疫分析法对不同时期的注定滞育和非滞育棉铃虫的血淋巴中的类固醇蜕皮素的含量进行了测定,发现在预蛹期间,注定滞育的棉铃虫的类固醇蜕皮素含量高于非滞育的棉铃虫,化蛹后,注定滞育的棉铃虫的类固醇蜕皮素含量则迅速降到极低的水平,明显低于非滞育棉铃虫。用20-羟基蜕皮素处理不同时期的滞育蛹,均能打破滞育。由此可见,类固醇蜕皮素含量的降低或缺乏乃是导致棉铃虫滞育的关键因子之一。     

Brain-independent development in the moth Sesamia nonagrioides

The caterpillars of Sesamia nonagrioides developing under long-day (LD) photoperiod pupate in the 5th or 6th instar whereas under short day (SD) conditions they enter diapause and undergo several extra larval molts. The diapause is terminated within 1-3 instars upon transfer of SD larvae to the LD conditions. Brain removal from the 6th instar larvae promotes pupation followed by imaginal development; however, one third of the SD larvae and 12% of the LD larvae debrained at the start of the instar first undergo 1-2 larval molts. The incidence of larval molts is enhanced by the brain implants. Exclusively pupal molts occur in the LD larvae debrained late in the 6th instar. Decapitation elicits pupation in both LD and SD larvae, except for some of the 4th and 5th and rarely 6th instar that are induced to a fast larval molt. The pupation of decapitated larvae is reverted to a larval molt by application of a juvenile hormone (JH) agonist. No molts occur in abdomens isolated from the head and thorax prior to the wandering stage. Abdomens isolated later undergo a larval (SD insects) or a pupal (LD insects) molt. Taken together the data reveal that in S. nonagrioides (1) several larval molts followed by a pupal and imaginal molt can occur without brain; (2) an unknown head factor outside the brain is needed for the pupal-adult molt; (3) brain exerts both stimulatory and inhibitory effect on the corpora allata (CA); (4) larval molts induced in CA absence suggest considerable JH persistence.     

Diapause termination in the spotted stem borer, Chilo partellus (Lepidoptera: Pyralidae) in the laboratory

The effect of temperature, photoperiod, artificial diet and water on the termination of diapause by larvae of the stem borer, Chilo partellus (Lepidoptera: Pyralidae), was studied in the laboratory. Termination of diapause as indicated by pupation was affected mainly by a combination of high temperature and a long day photoperiod. Total darkness did not prevent termination of diapause and pupation occurred also in larvae which were never exposed to water. Long days accelerated pupation, but, under 16 h daylength, termination of diapause was faster than under constant illumination. Provision of artificial diet had no effect or slowed down pupation but water decreased the time to pupation. Under 28°C, 16 h daylength and availability of water, C. partellus diapausing larvae terminated diapause and pupated in about 9 days.     

Food‐availability dependent premature metamorphosis in the bean blister beetle Epicauta gorhami (Coleoptera: Meloidae), a hypermetamorphic insect that feeds on grasshopper eggs in the larval stage

Larvae of the bean blister beetle, Epicauta gorhami, feed on only grasshopper eggs and undergo hypermetamorphosis with pseudopupal diapause in the fifth instar. Whether E. gorhami larvae enter pseudopupal diapause or pupate directly from the fourth instar is controlled by temperature and photoperiod. In nature, larvae are confronted with a significant variation in the availability of food, suggesting the possibility that feeding conditions may also affect the diapause incidence. Here, we addressed this issue by changing the feeding conditions in the fourth instar under conditions of 16 h light : 8 h dark (LD 16 : 8) at 25°C. Food deprivation reduced the length of instar and increased the tendency to pupate, leading to the early eclosion of a small adult. Even non‐feeding fourth‐instar larvae pupated. Regardless of the timing of food deprivation, the post‐feeding larval period was constant and equivalent to that of ad libitum‐fed larvae, suggesting that premature exhaustion of the food supply triggers the initiation of pupation. In agreement with these results, when larvae were fed on intact grasshopper egg pods of various sizes from four species, those that fed on smaller egg pods had a decreased tendency to pseudopupate (i.e., to enter diapause). Food‐deprived larvae showed a clearer photoperiodic response and had a shorter critical day‐length. Thus, in E. gorhami, feeding conditions do not affect pupation success, but do affect the tendency to pupate or pseudopupate. This is the first report of the occurrence of premature pupation in carnivorous insects. We discuss our findings in the context of the natural history and behavioral ecology of E. gorhami.     

Juvenile hormones and their titer regulation in Galleria mellonella

Juvenile hormones I, II and III occur in Galleria but JH II is dominant. Its concentration reaches a peak of 3 pmol/g body wt in the penultimate instar, drops to zero in the last larval instar and, except for a small peak in prepupae (0.2 pmol/g), remains undetectable until pharate adults. After emergence the titer reaches over 5 pmol/g in both sexes. Presence of JH II is associated with JH II acid; JH III acid occurs even more often, including stages lacking JH III. Brain implantation into freshly ecdysed last instar larvae effects a similar JH peak as in the penultimate instar and causes an extra larval molt. The opposite treatment, i.e. decerebration of fresh last instar larvae, elicits a continuous rise of JH II to 10 pmol/g and an increase of otherwise rare JH I to 3 pmol/g. Sham operations of these larvae or decerebration of old larvae elevate practically only JH II titer to 1–1.5 pmol/g. Implanted brain-corpora cardiaca-corpora allata complexes maintain in various hosts 0.14–1.6 pmol/g of JH II. The significance and regulation of these fluctuations in JH titer are discussed.     

苜蓿切叶蜂滞育的诱导因素研究

苜蓿切叶蜂Megachile rotundata(F.)预蛹的滞育主要受光周期和温度的影响。雌蜂感受光周期的变化是决定子代预蛹是否进入滞育的一个主要因素;当代的幼期,特别是高龄幼虫(约3龄)到预蛹这一阶段所感受的温度变化,对预蛹滞育有很大的影响,此期如果环境温度低于(21.59±1.03)℃,可有超过50%的个体进入滞育。此外,放蜂地区的纬度及蜂的代次对预蛹的滞育亦有重要的影响。     

Pupal diapause of Helicoverpa armigera (Lepidoptera: Noctuidae): sensitive stage for thermal induction in the Okayama (western Japan) population

Helicoverpa armigera (Hübner) exhibits a facultative pupal diapause, which depends on temperature and photoperiod. Pupal diapause is induced at 20 degrees C by short photoperiods and inhibited by long photoperiods during the larval stage. However, in some pupae (35% of males and 57% of females) of a non-selected field population from Okayama Prefecture (34.6 degrees N), diapause is not induced by short photoperiods. In the present experiment, the importance of temperature for diapause induction was studied in the non-diapausing strain, which was selected from such individuals reared at 20 degrees C under a short photoperiod of 10L:14D. Furthermore, the sensitive stage for thermal determination of pupal diapause was determined by transferring larvae of various instars and pupae between 20 degrees C and 15 degrees C. Diapause was induced by 15 degrees C without respect to photoperiod. When larvae or pupae reared from eggs at 20 degrees C under a short or a long photoperiod were transferred to 15 degrees C in the periods of the middle fifth instar to the first three days after pupation, the diapause induction rate was significantly reduced in both males and females, especially in females. In contrast, when larvae or pupae reared at 15 degrees C were transferred to 20 degrees C in the same periods, diapause was induced in males, but not in females. However, the diapause induction rate of pupae transferred to 20 degrees C on the fourth day after pupation was significantly increased in females. The results show that temperature is the major diapause cue in the photoperiod-insensitive strain and the periods of middle fifth larval instar to early pupal stage are the thermal sensitive stages for pupal diapause induction with some different responses to temperatures between males and females in H. armigera.     

Prothoracicotropic Hormone Acts as a Neuroendocrine Switch between Pupal Diapause and Adult Development

Diapause is a programmed developmental arrest that has evolved in a wide variety of organisms and allows them survive unfavorable seasons. This developmental state is particularly common in insects. Based on circumstantial evidence, pupal diapause has been hypothesized to result from a cessation of prothoracicotropic hormone (PTTH) secretion from the brain. Here, we provide direct evidence for this classical hypothesis by determining both the PTTH titer in the hemolymph and the PTTH content in the brain of diapause pupae in the cabbage army moth Mamestra brassicae. For this purpose, we cloned the PTTH gene, produced PTTH-specific antibodies, and developed a highly sensitive immunoassay for PTTH. While the hemolymph PTTH titer in non-diapause pupae was maintained at high levels after pupation, the titer in diapause pupae dropped to an undetectable level. In contrast, the PTTH content of the post-pupation brain was higher in diapause animals than in non-diapause animals. These results clearly demonstrate that diapause pupae have sufficient PTTH in their brain, but they do not release it into the hemolymph. Injecting PTTH into diapause pupae immediately after pupation induced adult development, showing that a lack of PTTH is a necessary and sufficient condition for inducing pupal diapause. Most interestingly, in diapause-destined larvae, lower hemolymph titers of PTTH and reduced PTTH gene expression were observed for 4 and 2 days, respectively, prior to pupation. This discovery demonstrates that the diapause program is already manifested in the PTTH neurons as early as the mid final instar stage.     

The hormonal regulation of the larval diapause in the codling moth, Laspeyresia pomonella (Lep. Tortricidae)

The hormonal control of the facultative diapause of the codling moth has been investigated. The diapause can be divided into 4 phases or periods: (1) diapause induction by short-day conditions (SD) in young larvae, (2) initiation of the diapause in the early last larval instar by a high titre of juvenile hormone, (3) onset and maintenance of diapause with inactivity of the neuroendocrine system, as evidenced by the results of neck-ligation experiments, (4)termination of diapause by the production of ecdysteroid.Diapause-induced larvae pupated after spinning the cocoon, if the state of induction was changed by injection with the anti-juvenile hormone precocene II at the beginning of the last larval instar and subsequent results of neck-ligation experiments, (4) termination of diapause by the production of ecdysteroid. treated with juvenile hormone during the first 1.5 days after the last larval moult and subsequently reared under SD. Under LD, continuous application of juvenile hormone during the last larval instar and after spinning did not prevent the insects from moulting to either a supernumerary larva, a pupa or a larval-pupal intermediate. Termination of diapause, i.e. pupation, was achieved by injecting diapausing larvae with 20-hydroxyecdysone. Although juvenile hormone was found to have a prothoractropic effect in diapausing larvae, no pupal moult could be induced by the application of the hormone. Contrary to the hormonal situation before pupation of nondiapausing larvae, no juvenile hormone could be detected before or during the pupation of larvae after diapause.     

Identification, characterization, and developmental regulation of two storage proteins in the bamboo borer Omphisa fuscidentalis

Two insect storage proteins, OfSP1 (75 kDa) and OfSP2 (72 kDa), were purified using three different chromatographies from the hemolymph of Omphisa fuscidentalis larvae during diapause, and their genes were cloned. OfSP1 and OfSP2 concentrations in the hemolymph were high during diapause. During pupation, OfSP1 levels decreased in the male hemolymph and disappeared from the female hemolymph. OfSP1 and OfSP2 mRNA levels in the fat bodies were low during the third instar, but increased greatly during the fourth and fifth larval instars. During diapause, mRNA expression continued at a lower level than during the feeding period. The injection of 20-hydroxyecdysone (20E) into diapausing larvae caused an increase in OfSP1 and OfSP2 mRNA levels 2-3 days post-injection, followed by a decrease in expression until pupation, which occurred 2-4 days thereafter. When larvae were treated with juvenile-hormone analog (JHA), OfSP1 and OfSP2 mRNA levels gradually decreased until the onset of pupation. In Omphisa, OfSP1 and OfSP2 proteins are produced and released by the larval fat bodies in the fourth and fifth-instar larvae, and the proteins accumulate in the hemolymph until the insects enter diapause. OfSP1 may be reabsorbed by the fat bodies at the end of diapause for subsequent re-use during pupation.     

Dopamine is a key factor for the induction of egg diapause of the silkworm, Bombyx mori.

The silkworm, Bombyx mori, enters diapause in the early embryonic stage. Embryonic diapause is induced by incubating eggs of the maternal generation at high temperature (diapause type), whereas incubation at low temperature results in non-diapausing progeny (non-diapause type). Measurement of catecholamine concentrations in haemolymph and brain-subesophageal ganglia (Br-SGs) showed that only dopamine concentrations in both tissues are consistently higher in diapause-type than non-diapause-type larvae and pupae. In particular, the difference in dopamine concentrations in both tissues increases around pupal ecdysis. During the early pupal stage, Dopa decarboxylase activities and mRNA concentrations in Br-SGs were also much higher in diapause-type than non-diapause-type insects. Elevation of dopamine levels induced by feeding Dopa to penultimate-instar and last-instar larvae, and by injecting Dopa or dopamine into pupae 2 days after pupation made the non-diapause-destined insects lay diapause-destined eggs at 59% and approximately 70% frequencies, respectively. Furthermore, injection of Dopa or dopamine elevated mRNA levels of the diapause hormone in the Br-SGs of non-diapause-type pupae 1 day after injection. Incubation of Br-SGs isolated from non-diapause-type day-2 pupae with Dopa or dopamine also stimulated the expression of diapause hormone mRNA. These data indicate that environmental stimuli during embryonic development increase dopamine levels in both hemolymph and Br-SGs from the larval stage to early pupal stage, which results in laying of diapause-destined eggs by female adults through enhanced expression of the diapause hormone gene.