Activité comparée des hormones juvéniles en C-18 (JH-I) et en C-16 (JH-III) chez Locusta migratoria

The comparative activity of C-16 and C-18 juvenile hormones is studied in Locusta migratoria on four well-known physiological functions of the corpora allata by means of a single injection of a solution of hormone in oil at doses of 50, 100, and 200 μg/animal. Judged on morphogenesis and pigmentation, JH-I (C-18 JH) as well as JH-III (C-16 JH) show a real juvenilizing effect. The potency of JH-I is much higher than that of JH-III because the first hormone only produces supernumerary larvae and most modified green animals. JH-I counterbalances exactly the lack of CA on the gonadotropic function whereas JH-III allows only about 50 per cent development of oöcytes. The cardiotropic activity of JH-I is similar to that of the CA. The C-18 juvenile hormone is until now the only studied ‘juvenilizing’ compound which increases the heartbeat. JH-III appears to have no noticeable effect on the heart.These results combine to prove that only JH-I has an activity similar to the Locusta corpora allata on morphogenesis, pigmentation, ovarian maturation, and the cardiac activity of L. migratoria.     

Effects of electrocoagulation of cerebral neurosecretory cells and implantation of corpora allata on oöcyte development in Locusta migratoria

The implantation of active corpora allata into intact Locusta females during growth accelerates pre-vitellogenic oöcyte growth and vitellogenesis. Localised stimulation of yolk deposition follows the implantation of active corpora allata between the ovarioles demonstrating a gonadotrophic rôle for the corpus allatum hormone. Electrocoagulation of the median neurosecretory cells of the brain prevents vitellogenesis whilst pre-vitellogenic oöcyte growth occurs normally. Implantation of active corpora allata into females with ablated cerebral neurosecretory cells promotes vitellogenesis in a proportion of test animals although mature oöcytes are never produced.It is suggested that the rôle of the median neurosecretory cells during egg development in Locusta is primarily concerned with the activation and maintenance of activity of the corpora allata. The corpus allatum hormone acts both metabolically and gonadotrophically.     

In vivo stimulation of vitellogenesis in Aedes aegypti with juvenile hormone,juvenile hormone analogue (ZR 515) and 20-hydroxyecdysone

Decapitated blood-fed Aedes aegypti mosquitoes do not undergo normal oöcyte maturation. Topical application of 1.25 ng JH analogue (ZR 515) or 250 ng JH-I restored ovarian development in 70–80% of the treated females. The rate of vitellogenin synthesis in these animals was 80% of normal blood-fed controls.When ligated abdomens were treated, 125 pg ZR 515 or 12.5 ng JH-I were sufficient to restore ovarian development in 80% of the animals. The rate of vitellogenin synthesis in these animals was 70% of normal blood-fed controls. On the other hand, injection of 1.25 μg 20-hydroxyecdysone was needed to restore ovarian development and vitellogenin synthesis in decapitated and abdominally ligated females.These experiments indicate that JH concentrations closer to the physiological norm than 20-hydroxyecdysone, can restore ovarian development and vitellogenin synthesis in vivo.     

Culture in vitro des ovaires de Tenebrio molitor. Hormone juvénile,vitellogenèse,et survie des jeunes ovocytes

In vitro culture of the ovaries of adult Tenebrio molitor is possible on a medium deprived of chick embryo extract. Ovarian and muscular tissue extracts ensure the young oöcytes survival by trophic action. Vitellogenic proteins present in the culture medium enter the oöcytes without the intervention of the corpora allata hormone. Juvenile hormone does not exert a gonadotrophic function in T. molitor.     

Rate of follicle growth,change in follicle volume and stages of macromolecular synthesis during ovarian development in Musca domestica

At 21°C the first egg generation takes 6 days to develop. During this period the oöcyte volume increases by a factor of ×5000, and compared with an oögonium the growth factor amounts to ×100,000. The growth rate of the oöcyte increases with each stage of oögenesis, until at stage 5 it reaches 2.5 × 10⁶ μm³/hr. About 35% of the substance stored in the oöcyte originates from the nurse chamber. 30% of the volume is formed in the stage where the oöcyte synthesizes almost exclusively glycogen. Accordingly, about 30% of the volume is provided by the euplasmatic protein synthesis and by the yolk uptake.     

Juvenile hormone and its assay in virgin adult Blattella germanica females

The physiological bases for the gonadotrophic assay as presented by Kunkel were confirmed, and the assay method was found to be reproducible. However, the assay method was not found to be as useful as presented, due to the departure from linearity of the ovarian growth response above a hormone level of 5 μg/μl. Juvenile hormone (JH) titre higher than this level results in a depression of terminal oöcyte growth. Therefore, a valid assay of activity cannot be based on a single concentration.By injection, JH and FMC 23509 (10,11-epoxy-N-ethyl-3,7,11-trimethyl-2,6-dodecadienamide) were approximately equal in gonadotrophic activity. Topical application of FMC 23509 resulted in terminal oöcyte length of 2.45 mm in comparison to a length of 1.28 mm after injection of the same amount. This agrees with previous observations that such compounds are more active topically than by injection.     

Effect of photoperiod and temperature on reproduction of the monarch butterfly,Danaus plexippus

Optimal posteclosion ovarian development in monarch butterflies occurs at about 28°C. Higher and lower temperatures appear progressively inhibitory. Reproductive gland development in males follows a similar pattern. Juvenile hormone injections stimulate oöcyte maturation in animals held at 20 and 35°C but are most effective at the higher temperature. Juvenile hormone injections are ineffective at 10 and 15°C. The stimulatory effect of increasing photophase on ovarian development was most apparent at optimal temperature. The possible significance of our findings to monarch migration is discussed.     

Mosquito juvenile hormone: Identification and bioassay activity

Juvenile hormone III was identified in whole-body extracts of larval and adult Aedes aegypti. No juvenile hormone I or II was detected. The activity of juvenile hormones I, II and III, as well as two juvenile hormone analogues (methoprene, or ZR-515 and ZR-371) was examined in adults, whereas the activity of only the three naturally occurring hormones was studied in larvae. In the larval assay fourth-instar larvae were exposed to the juvenile hormones and their ability to eclose normally was measured. In the adult assay, abdomens were removed shortly after eclosion and the juvenile hormones or analogues were applied topically. Growth of the oöcytes to the resting stage was measured. In larval and adult bioassays juvenile hormone I was 10 × and 25 × more active, respectively, than juvenile hormone III. The bioassay and titre data taken together suggest that juvenile hormone III is the sole physiologically necessary juvenile hormone in Aedes.     

The role of factors from the head in the regulation of egg development in the mosquito Aedes aegypti

The relationships between the release of factors from the head after blood-feeding, subsequent levels of ecdysteroids and vitellin, and the ultimate maturation of eggs in Aedes aegypti were investigated. Females were decapitated at various times after a blood meal, at 20 or 48 h after feeding the animals were dissected and divided into two groups, those with arrested oöcytes (yolk length < 100 μm) and those with maturing oöcytes (yolk length > 100 μm). These yolk lengths correspond with the levels of oöcyte growth believed to accompany the proposed initiation and promotion phases of egg development. Animals dissected at 20 h were assayed for ecdysteroid by radioimmunoassay; those dissected at 48 h were assayed for vitellin by rocket immunoelectrophoresis.Non-blood-fed unoperated females contained 8% as much ecdysteroid as blood-fed controls and no measurable vitellin. Females with arrested oöcytes (< 100 μm) were obtained only if decapitations were performed before 8 h; these females had about 20% of the ecdysteroids and 8% of the vitellogenin normally found in blood-fed animals. Females decapitated between 2 and 8 h with maturing oöcytes contained 50–60% as much ecdysteroid and vitellin as blood-fed unoperated controls. Normal ecdysteroid and vitellin levels were reached only when decapitations were delayed for 12 and 24 h, respectively. The number of developing oöcytes was also decreased by early decapitation and was closely correlated with vitellin levels.We conclude that the egg development neurosecretory hormone is released twice, once before 8 h and once after 8 h, to control ecdysteroid levels. We also suggest the presence of other factors from the head that control vitellin levels, the number of developing oöcytes, and the early growth of the oöcyte (initiation).     

Enhancement of juvenile hormone biosynthesis in locusts following electrostimulation of cerebral neurosecretory cells

Electrostimulation of the medial neurosecretory cells of day-1 adult female Locusta migratoria resulted in a significant enhancement of juvenile hormone biosynthesis by the corpora allata within 2–3 days of the operation, as determined by a radiochemical assay for juvenile hormone biosynthesis. This elevation in the rate of juvenile hormone biosynthesis was also reflected in basal oöcyte length, with the oöcytes of stimulated animals significantly larger than the sham-operated animals. Radio-frequency cautery of the cerebral axonal tracts of the medial neurosecretory cells prevented this enhancement in juvenile hormone biosynthesis and in basal oöcyte growth in both stimulated and sham-operated animals.Stimulation of the lateral neurosecretory cells resulted in a slight elevation in rates of juvenile hormone biosynthesis 2 days after the operation. However, after cautery of the medial cell tracts, a significant elevation in juvenile hormone biosynthesis was observed 1 and 2 days after stimulation. Basal oöcyte length in stimulated animals differed significantly from sham-operated animals only on day 6. Cautery of the medial cell tracts again attenuated oöcyte growth. Our results suggest that the medial neurosecretory cells are the source of an allatotropin that can be released by electrostimulation. This substance appears to operate directly on the corpus allatum, causing a change in the juvenile hormone biosynthetic machinery.     

Juvenile hormone: Its assay and effects on pupae of Manduca sexta

Non-diapausing pupae of Manduca sexta were used to develop a bioassay for juvenile hormone (JH). The period of maximal sensitivity to Cecropia C17-JH injected in olive oil was found to be 24 to 30 hr after pupal ecdysis at the time of the beginning of epidermal retraction. The dose-response curves for C16-, C17-, and C18-JH at 29±1 hr after pupal ecdysis were determined and those for the latter two compounds were found to be similar and to be linear between 10^?2 and 10 μg/g body weight. C16-JH was 300 times less active than C17- and C18-JH in this bioassay. The effectiveness of 0·5 μg/g C18-JH at 29±1 hr was determined by the carrier media in which it was injected. The highest scores were obtained when the carrier was light mineral oil or loive oil whereas the lowest scores were obtained using 10% BSA or Tween 80. These scores are consistent with the kinetics of equilibration of the injected JH with the haemolymph. Thus, the injected hormone is more effective when it slowly leaks into the blood, presumably because it is metabolized much more slowly.     

Eclosion and hatching in cockroach first instar larvae: A stereotyped pattern of behaviour

Cockroach pharate first instar larvae (Periplaneta americana) spontaneously initiate eclosion and hatch from the oötheca after 30 days' incubation at 29°C. The caudal-to-rostral peristaltic movements involved in both eclosion and hatching are initiated even when the first instar larvae have been removed from the oötheca and incubated separately in organ culture dishes. Therefore, environmental stimuli and conditions in situ are not necessary for the onset of eclosion. However, environmental factors associated with the cuticle control the termination and/or duration of the eclosion behaviour sequence. Larvae which had cuticles glued to their bodies had longer than normal eclosion episodes while larvae which experienced premature cuticle removal immediately ceased the movements. Cuticle removal immediately ‘switched’ behaviour from that of the larva to that of the adult with the characteristic walking gait. Eclosion in larvae removed from the oötheca could be initiated by tactile stimulation. A rôle for this response in synchronizing the eclosion-hatching movements of the many larvae within an oötheca is suggested.     

Factors responsible for the initiation of a second oöcyte maturation cycle in the ovoviviparous cockroach Nauphoeta cinerea

The factors responsible for the initiation of a second oöcyte maturation cycle were investigated by measuring oöcyte growth, vitellogenin titre, and corpus allatum activity after injection of juvenile hormone and/or removal of the egg-case from pregnant females and by performing ovary and corpus allatum transplant experiments.Egg-case removal in late pregnancy results in immediate oöcyte growth, whereas in early pregnancy oöcyte growth is resumed only after a lapse of time, even after injection of juvenile hormone. This, however, induces an immediate increase in the haemolymph vitellogenin titre. A single injection of 2 or 10 μg of juvenile hormone II first stimulates some oöcyte growth after this lapse of time and later activates the corpora allata, which in turn leads to completion of oöcyte maturation. A repeat injection of 10 μg stimulates continuous oöcyte growth without activating the corpora allata. In the presence of an egg case, activation of the corpora allata is suppressed, even after injection of 2 μg of juvenile hormone III, and the oöcytes do not grow. Injection of higher doses stimulates oöcyte growth and leads to expulsion of the egg case in up to 95% of the females. This, however, is not a direct consequence of the increase in size of the ovaries. Ovary transplant experiment show that in young pregnant females the second generation of oöcyte is not yet competent for growth and that ovaries which are competent can mature in young pregnant females, treated with juvenile hormone, whose egg case has been removed.The results are summarized in a model demonstrating the various factors involved in regulating corpus allatum activity in oöcyte maturation and pregnancy and after application of juvenile hormone. We prepose that the corpus allatum activating effect of exogenous juvenile hormone is mediated by the growing oöcyte and that this activation can be suppressed by the continuous presence of exogenous juvenile hormone.     

Endocrine control of oögenesis in the housefly,Musca domestica vicina

The endocrine system involved in the control of oögenesis in the housefly, Musca domestica vicina, was investigated. Allatectomy, decapitation, and starvation of newly emerged females resulted in inhibition of oögenesis, showing a close relationship between enlargement of the corpus allatum and growth of follicles during the first oögenesis. Histological observation of sexually matured females showed active secretion of the corpus allatum and the medial neurosecretory cells of pars intercerebralis. Topical application of juvenile hormone analogues (JHA) to the allatectomized fly induced the growth of ovary, and critical doses of methoprene and methyl-7, 11-diethyl-juvenate for the maturation of the ovary were determined. JHA stimulated initiationof oögenesis in the starved or decapitated flies as well as vitellogenesis in the sugar-fed one; subsequently it was found that juvenile hormone acted not only as a gonadotropin but also as a regulator of vitellogenesis. Furthermore, JHA stimulated cell lysis in pupal fat body of female flies, indicating a possible influence of juvenile hormone upon the process of releasing vitellogenin.     

The endocrine basis of reproductive inactivity in Monarch butterflies overwintering in central California

Monarch butterflies (Danaus plexippus) collected during winter in central California are reproductively inactive. Oögenesis is stimulated in such animals by environments simulating summer conditions. Allatectomized or neck-ligatured winter animals do not normally undergo oögenesis when placed in summer conditions, but apparently normal oögenesis occurs if they are injected with juvenile hormone isomers. Injections of such isomers into winter animals held in environments simulating winter also promote oögenesis, even though winter conditions typically inhibit ovarian development. Reproductive dormany in winter Monarchs of central California therefore appears to be due (at least partially) to environmentally induced inactivity of the corpora allata.     

Description of the oöcysts of two new species of Eimeria (Apicomplexa: Eimeriidae) from the rough earth snake Virginia striatula (Serpentes: Colubridae) in Texas and Arkansas

Coccidian oöcysts recovered from the faeces of rough earth snakes Virginia striatula (Serpentes: Colubridae) were found to represent two previously unreported eimerians. Oöcysts of Eimeria desotoensis n. sp. were found in 5/32 (16%) of the snakes and were spherical to ellipsoidal, 18.4 × 17.2 (15–21.5 × 15–19.5) μm, with a thin, single-layered wall; their shape-index (length/width) was 1.07 (1.00–1.23). A micropyle and oöcyst residuum were absent; polar granule were present in 33% of the oöcysts. The sporocysts were ovoidal, 11.5 × 7.6 (10.5–13 × 7–8) μm, with a Stieda body; their shape-index was 1.51 (1.30–1.68). The sporocyst residuum was moderate in size and composed of a cluster of granules. Oöcysts of Eimeria hobartsmithi n. sp. were found in 2/32 (6%) of the snakes and were subspherical to ellipsoidal, 18.0 × 15.7 (16–20 × 15–17) μm, with a thin, single-layered wall; their shape-index was 1.15 (1.02–1.32). A micropyle, oöcyst residuum and polar granule were absent. The sporocysts were elongate, 13.2 × 6.3 (12–14.5 × 6–6.5) μm, with a Stieda body; their shape-index was 2.10 (1.88–2.34). A large sporocyst residuum was present in each sporocyst, often obscuring the sporozoites. In addition to the two new species, oöcysts of E. striatula Upton & McAllister, 1990 were observed in 38% of the snakes.     

Two new species of <Emphasis Type="Italic">Eimeria</Emphasis> Schneider, 1875 (Apicomplexa: Eimeriidae) from <Emphasis Type="Italic">Gerbilliscus guineae</Emphasis> Thomas (Rodentia: Gerbillinae) in the Niokolo Koba National Park,Senegal

We describe two new species of Eimeria Schneider, 1875 from the gerbiline rodent Gerbilliscus guineae in the Niokolo Koba National Park, Senegal. Faecal examination of samples revealed the presence of sporulated oöcysts of two eimerian coccidia, both possessing an oöcyst residuum. Eimeria permira n. sp. is remarkable in terms of oöcyst size and oöcyst wall texture. Sporulated oöcysts are ellipsoidal, 45.8 (42–50) × 32.5 (31–38) μm; the oöcyst wall is 3–4 μm thick, composed of three layers, with the outer layer sheathed by rough granular material; and the sporocysts are broadly ellipsoidal, 15.4 (15–16) × 11 and with a Stieda body present. Oöcysts of Eimeria gerbillisci n. sp. are subspherical, 22.5 (19.5–24) × 18.8 (16.5–20) μm, with a colourless, faintly granulated oöcyst wall 1.5 thick; and the sporocysts are 10.1 (10–12) × 6.7 (6–8), broadly ellipsoidal and often somewhat pointed towards both ends.     

Actions of the juvenile hormone, 20-hydroxy-ecdysone,and the oöstatic hormone during oögenesis in the flies Phormia regina and Sarcophaga bullata

Application of juvenile hormone (JH) to sugar-fed Phormia flies leads to full ovarian development, i.e. the flies become autogenous. Application of JH to sugar + liver-fed Phormia leads to the simultaneous development of primary, secondary and tertiary oöcytes, suggesting the role of the oöstatic hormone is to shut off the action of the JH. This is consistent with the notion that the oöstatic hormone may act on the corpus allatum either directly or through the neurosecretory system. Application of 20-hydroxy-ecdysone to Phormia or Sarcophaga, when primary oöcytes have started to develop (stage 4A), causes the primary oöcytes to degenerate, with concomitant development of the secondary oöcytes.     

The effects of nutrition and methoprene treatment on ovarian ecdysteroid synthesis in Drosophila melanogaster

Radioimmunoassay of in vitro culture medium from ovaries of Drosophila melanogaster indicates that detectable ovarian ecdysteroid synthesis begins between 6 and 12 h after eclosion and reaches a peak between 24 and 30 h, when animals are reared at 25°C, 12 h photophase. Analysis of 24 and 72 h medium by a combination of high-performance liquid chromatography and radioimmunoassay demonstrates three ecdysteroid regions, two comigrating with known standards of ecdysone and 20-hydroxyecdysone and a third highly polar region containing one or more unidentified radioimmunoassay-active ecdysteroids. In 72 h medium the polar region comprises the majority of radioimmunoassay-active material while in 24 h medium the majority is in the ecdysone region. Provision of a nutritionally deficient diet to females at adult eclosion prevents the normal increase in vitellogenic-stage follicles and ovarian ecdysteroid synthesis. Methoprene treatment of such females stimulates a transient burst of ovarian ecdysteroid synthesis and the production of near normal numbers of vitellogenic oöcytes by 24 h, although by 48 h the number of vitellogenic oöcytes is less than normal.     

The effects of starvation and subsequent feeding on juvenile hormone synthesis and oöcyte growth in Schistocerca americana gregaria

The effect of starvation on the synthesis of C₁₆ juvenile hormone (JH) and the growth of terminal oöcytes was assessed in Schistocerca americana gregaria at two times during adult life: before activation of the corpora allata and during the first gonotrophic cycle. In both groups, starvation resulted in a decline in JH synthesis within 2–3 days and rates of synthesis remained low throughout the experimental period. The growth rate of oöcytes which were not vitellogenic at the time of starvation was depressed whereas the percentage of resorption of vitellogenic oöcytes increased dramatically with starvation. Although the percentage of resorption increased in animals with vitellogenic oöcytes, some mature oöcytes were produced, particularly in animals in which the oöcytes were greater than 5 mm in length at the time of starvation. This suggests that oöcyte maturation can be divided into two distinct phases—an early phase of vitellogenesis associated with high rates of JH synthesis and a late phase, in oöcytes greater than 5 mm, associated with much lower rates of JH synthesis.Stimulation of JH synthesis by farnesenic acid in 5-day starved animals resulted in high rates of JH synthesis, indicating that starvation did not appreciably alter the enzymic activities of the final two stages in JH synthesis. Thus rate limitation did not occur at these stages.Feeding of 5-day starved animals resulted in a transient increase in the rate of JH synthesis. However, rates of JH synthesis and oöcyte growth remained subnormal throughout the observation period, suggesting that the effects of starvation cannot be entirely reversed by feeding. Thus starvation may decrease the reproductive potential of the females.