Effect of injection of synthetic Hyalophora cecropia juvenile hormone in Locusta migratoria L]

The synthetic racemic C18 Hyalophora cecropia juvenile hormone (JH-I) is injected at does of between 10 and 200 mug/animal at the end of the fourth instar of Locusta migratoria. The effects on mortality, length of the fourth and fifth instars, pigmentation and morphogenesis are reported. Higher doses of JH-I produce a higher mortality than lower doses. But mortality can also occur following the injection of oil which sometimes takes place only a few hours before the ecdysis. In no case is JH-I able to shorten the length of the instar. Many animals moult at the same time as the controls, but some of them, both in the fourth and fifth instars, show an important increase in the length of the instar because of an inhibition of the ecdysis. The effect of JH-I on pigmentation is very important and doses higher than 50 mug/animal present a greater effect than an implantation of one pair of corpora allata, both on the number of insects which turn green and on the intensity of this green pigmentation. At the metamorphosis the larvae injected with JH-I produce imperfect imagos and supernumerary larvae, the number of which depends upon the dose. Nevertheless the morphogenetic effect is considerably lower than that of one pair of corpora allata. We have reason to think that this is only due to the time of injection and not to the activity on morphogeneis of the injected hormone. JH-I is injected at the dose of 200 mug in young females which were allatectomized beforehand to prevent oocytes maturation. The hormone completely counter-balances the lack of the corpora allata and some days after the injection the oocytes are in the same state of development as those of the controls. All the results indicate that the synthetic racemic C18 juvenile hormone of Hyalophora cecropia shows a quite similar activity to the secretion of the corpora allata on Locusta migratoria although it has been said for some time that this hormone was not the principal one in locusts.     

Activite de l'hormone juvenile en C17 (JH-II) chez Locusta migratoria

The effects of C₁₇ juvenile hormone (JH-II) have been investigated in Locusta on morphogenesis, ovarial development, and pigmentation, by means of injections in oil. These effects have been compared with those of injecting C₁₈ juvenile hormone (JH-I) and of implanting corpora allata into Locusta. JH-I and JH-II are similar in their effects upon morphogenesis and pigmentation, and also on ovarial development in which JH-III has been found to be more effective in other insects. Injections of JH-I and JH-II have similar effects to those seen after implanting corpora allata. However in experiments on heart beat (in which the corpora allata have been shown to be involved) JH-I is the only substance to increase the rate of heart beat in the same way as active corpora allata. These observations are discussed, and it is concluded that JH-I is the hormone with effects nearest to those of the corpus allatum hormone itself.     

Some effects of amputation of the antennae on pigmentation, growth and development in the locust, Schistocerca gregaria

ABSTRACT. Removal of the antennae from Schistocerca gregaria early in the third or fourth instar resulted in fifth instar nymphs with a green haemolymph and cuticle. Antennectomized adults had a lower somatic dry weight and a smaller fat body than operated control insects. In addition, their rate of sexual development increased and some of their morphometric parameters were altered. Implantation of corpora allata into fourth instar nymphs induced a green coloration of the haemolymph after a few days. It is suggested that antennectomy of Schistocerca nymphs resulted in an increased effectiveness of the corpus allatum hormone with its concomitant effects on nymphal pigmentation, growth and development, and adult morphometries. It is further suggested that antennectomy of crowded locusts may mimic, for them, the uncrowded condition, by reducing sensory input.     

Influence of juvenile hormone on growth and digestion in fifth instar larvae and adults of Locusta migratoria

Food utilization was measured in female fifth instar larvae and adults of the migratory locust by following the weight of food ingested, the weight of faeces produced, and the increase in body weight. These parameters were measured in normally developing locusts, in locusts that had been implanted with a pair of active corpora allata (CA) in the beginning of the fifth instar period, and in allatectomized locusts, operated on the first day after adult ecdysis.A high titre of corpus allatum hormone results in a considerably higher water content of the insects; allatectomy reduces this content. The dry weight of the locusts is not essentially influenced by excess or absence of juvenile hormone.Food consumption in corpora-allata-implanted locusts does not differ from that in normally developing insects. Within each developmental period the digestive capacity remains constant, but the absolute value of this capacity may differ between the two developmental periods. The approximate digestibility is somewhat higher after CA-implantation and lower after allatectomy. The efficiency of conversion of digested food into body substance is greater in normally developing larvae than in adults. CA-implantation lowers this efficiency in developing larvae. Allatectomy slightly raises the efficiency of conversion in adult locusts.In the second half period of larval development, CA-implantation raises the respiratory rate, as estimated by measuring oxygen consumption. During adult development no significant influence of CA-implantation on respiration was established. Relations between the amount of food digested, the efficiency of conversion of digested food into body substance, and the respiratory activity are discussed.     

The activity of the corpora allata in the fourth and fifth larval instars of the migratory locust

The presence of juvenile hormone in the haemolymph of larvae of Locusta has been detected by a modified Galleria bioassay and these results are compared with indirect methods of estimating corpus allatum activity. Juvenile hormone is present in the haemolymph during the fourth larval instar except on the last day of the instar, and is absent from the haemolymph of the fifth and final larval instar except on the last day of the instar. Changes in the volumes of the corpora allata simply reflect changes in the growth of the whole insect and are of no value in predicting endocrine activity. Changes in the size of the cells of the corpora allata can be correlated with the presence of juvenile hormone in the haemolymph in the fourth larval instar, but similar changes in cell size occur in the fifth larval instar when no juvenile hormone is present in the haemolymph. The effects of the implantation of corpora allata are unreliable as estimates of corpus allatum activity as isolated corpora allata from fifth instar larvae release juvenile hormone. Indirect methods of measuring corpus allatum activity are thus shown to be unreliable. The R_f value of Locusta juvenile hormone as determined by thin-layer chromatography differs from that of Roeller's juvenile hormone, suggesting that the two hormones might be chemically distinct.     

Quantitative studies on the activity of the corpora allata in adult male Locusta and Schistocerca

Juvenile hormone has been detected in the haemolymph and corpora allata of adult male Locusta and the haemolymph of adult male Schistocera by a modified Galleria bioassay. The hormone was readily detected in the haemolymph of insects immediately after the final ecdysis, but then became difficult to detect until 2 days prior to the onset of sexual maturation. In sexually mature insects the titre of juvenile hormone was maintained at a constant level. The corpora allata of adult male Locusta increased in size throughout adult life. The juvenile hormone content of the corpora allata was low during the period of somatic growth, but increased at the onset of sexual maturation. Sectioning of the nervi corporis allati I in insects immediately after the final ecdysis prevented the normal increase in size of the corpora allata, but did not render them inactive since juvenile hormone was detected in the haemolymph after the operation. The half life of juvenile hormone in the haemolymph of allatectomized adult male Locusta was 1 to 2 hr.     

Juvenile hormone-dependent vitellogenin synthesis in Locusta migratoria fat body: Inducibility related to sex and stage

Juvenile hormone (JH)-dependent vitellogenin (Vg) synthesis in the fat body of Locusta migratoria is normally limited to sexually mature adult females. As a step toward examining the basis of this limitation, we have tested female and male locusts in a series of stages after the third larval molt for inducibility of Vg synthesis by the synthetic JH analog, methoprene. We find that in the fourth and fifth larval instars fat body of both sexes can be induced to produce Vg, but in the adult stage females respond strongly while no more than trace amounts can be induced in males. Quantitative assays show relative responsiveness in the order: adult female > fifth instar female > fifth instar male ? adult male. During the fifth instar of both sexes, maximal vitellogenic response was obtained in midinstar. After the larval-adult ecdysis, female fat body was unresponsive during the first 4 days, then responsiveness increased and by Day 8 after ecdysis fat bodies were fully as competent to produce Vg as at Day 14, the usual maximum of the first vitellogenic cycle due to endogenous JH. Larval and adult female fat bodies implanted into male larvae are competent for Vg synthesis after metamorphosis, so that the differences between adult male and female cannot be imposed by the male milieu intérieur during the larval-adult molt. In male and female precocious adults, produced by treatment of fourth instars with precocene, fat body responded to methoprene as in normal adults. We conclude that factors intrinsic to the fat body cells, determined early in development, are responsible for differential gene programing in males and females, which is partially expressed by the fifth instar but fully manifest only after a molt in the absence of JH.     

Developmental changes in urea concentrations in the haemolymph of Daizo (T), an original strain of the silkworm,Bombyx mori reared on an artificial diet and on fresh mulberry leaves

Urea concentrations in the haemolymph of Daizo (T), an original strain of the silkworm, Bombyx mori, reared on an artificial diet and on fresh mulberry leaves were determined by a urease-indophenol method during the larval-pupal-adult development. Urea concentrations in the fourth and fifth instar larvae reared on an artificial diet (diet I) were between 0.10 and 0.15 mg urea N/ml haemolymph, and increased during the larval-pupal transformation to reach 0.33 mg/ml at the larval-pupal ecdysis. A further increase was observed during pupal-adult development and finally reached 0.48 mg/ml at day 7 pharate adult. In the fourth and fifth instar larvae reared on fresh mulberry leaves, the concentrations were low (0.05 mg/ml). From the larval-pupal ecdysis until day 8 pharate adult, further low urea concentrations (0.04 mg/ml) were observed. By starvation from 72 hr of the fifth instar larvae reared on another artificial diet (diet II), the elevation of urea concentrations (between 1.4- and 3.0-fold against the controls) was observed from just after starvation until day 1 spinning. From day 5 pupae, both the starved and the control insects showed a marked elevation of urea concentrations in the haemolymph, which was never observed on animals reared on diet I.     

Effect of fumigation and juvenile hormone on oxygen consumption of the larvae of Corcyra cephalonica (Stainton)

Reduced effect of JH-I, JH-II and JH-III on oxygen consumption of II-V instars and increased effect on the oxygen consumption of VI instar larvae suggested that control of corcyra with juvenile hormones could be brought about only when applied to just emerged VI instar larvae. Similarly fumigation of juvenile hormone treated larvae could prove beneficial only at VI instar stage. The possibility of enhancing the effect of fumigant with pretreatment of JH will be futile as even only JH treated VI instar larvae develop into abnormal individuals which die later.     

Compactin inhibits insect HMG-CoA reductase and juvenile hormone biosynthesis

The activity of 3-hydroxy-3-methylglutaryl CoA reductase in homogenates of the corpora allata of the tobacco hornworm, $\text{Manduca sexta}$, was competitively inhibited by compactin. The K_I for the sodium salt form of compactin was 0.9 nM for the reductase from both male and female corpora allata. In intact female corpora allata juvenile hormone biosynthesis was also inhibited by approximately 50 percent at 10 nM compactin. Following injection with compactin, darkening of the cuticle, an indication of juvenile hormone deficiency, was observed in larvae after ecdysis from third to fourth instar. Hence, compactin shows potential as an inhibitor of insect growth and development.     

Actions juvénilisante,chromatotrope, gonadotrope,et cardiotrope de- JH-III sur Locusta migratoria

The effects of JH-III, a chemical compound close to JH, are studied on different functions in which the corpora allata are involved. JH-III shows a clear prothoracotropic effect by shortening the length of the instar in which it is injected. Doses which comprised between 50 and 200μg/animal have a real juvenilizing and chromatotropic effect. But in all cases the effect is lower because this one is produced by the same doses of JH or by an implantation of one pair of corpora allata. JH-III allows the oöcytes of allatectomized females to develop. On control insects JH-III is not able to increase cardiac activity but at doses of 200 μg/animal it counterbalances the 10 per cent decrease brought about by allatectomy.JH-III, despite its chemically closeness to natural JH, appears to be less potent than more distant compounds such as Altozar and Altosid.     

L'action differentielle des hormones juveniles sur la metamorphose chez Locusta migratoria

The morphogenetic effect on metamorphosis of the three juvenile hormones is studied under experimental conditions that permit accurate conclusions in Locusta migratoria. Injections are made at the beginning on the last larval instar, which is the best time for action at the optimum level on the control of metamorphosis. Racemic hormones in stereochemical form comparable to that of natural compounds were used. Doses were chosen between 5 and 50 μg in order to give clear morphogenetic effects and give effects at a physiological level.A chronological study showed that juvenile hormones have the most important morphogenetic effect when injected in the first 40 hr of the last larval instar. Oiled solutions, stored at 4°C, lost only a small part of their morphogenetic activity after 9 months.Among the three hormones, JH-III presented the weaker morphogenetic effect, very significantly different from that of JH-I and JH-II. It has been possible to dissociate the effects of JH-I and JH-II on metamorphosis, JH-I giving a more potent action.     

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.     

Influence of a juvenile hormone analogue on vitellogenin synthesis and oögenesis in larvae of Nauphoeta cinerea

In experiments on the synthesis of the vitellogenic protein, farnesylmethylester, a juvenile hormone (JH) analogue, was injected into female Nauphoeta cinerea larvae at various stages during their development. Two and 4 days after injection, 2 μl of haemolymph were assayed in a vitellogenin immunodiffusion test. In second last and last instar larvae less than 6 days before adult ecdysis, high doses (100 μg) of farnesylmethylester are necessary to induce vitellogenin synthesis, whereas older last stage larvae and decapitated adults respond to small doses (1 μg) with the synthesis of vitellogenin. It seems that the competence to synthesize the vitellogenic protein changes at the time of induction of the moulting process. If farnesylmethylester is injected into last instar larvae with a supposedly high titre of ecdysone, the vitellogenic protein can be detected in the haemolymph of a small percentage of animals only.Oöcyte maturation can be observed in last instar larvae injected after the fifth to ninth day with farnesylmethylester. The observed volume changes of the corpora allata suggest that an absence of JH for a short time is necessary for the oöcytes to become competent to grow. Last instar larvae treated with farnesylmethylester become larval-adult intermediates with partly developed oöcytes, demonstrating a simultaneous juvenilizing and gonadotropic influence of the JH analogue. In last instar larvae injected with farnesylmethylester a partial degeneration of already maturing oöcytes is induced at the time when the ecdysone titre is supposedly high and the possible reasons for this are discussed.     

Hormonal control of egg maturation in the corn earworm, Heliothis zea

At eclosion, the ovaries of female Corn earworm Heliothis zea do not contain mature eggs. Virgin-unfed females produced approximately 400 mature eggs in 8 days; mating or feeding doubled this number, and mating plus feeding more than tripled it. Females allatectomized or decapitated at day O matured few eggs. Egg production was restored by implantation of active corpora allata (CA) or by treatment with the juvenile hormone (JH) analogue methoprene at day 0. 20-Hydroxyecdysone, on the other hand, had no effect. Females in which the CA had been denervated or in which the median neurosecretory cells of the brain had been ablated at day O produced fewer eggs than sham-operated animals. These results indicate that egg maturation is controlled by JH and that continuous input from the brain is required for sustained CA activity for maintaining a high rates of egg maturation.The rate of JH biosynthesis by CA in vitro was determined with a radiochemical assay. The major hormones produced were JH-II and JH-III with small quantities of JH-I. The rates of JH synthesis were similar in all experimental groups which may indicate that the in vitro rate of JH synthesis does not reflect the actual state of CA activity in the female.     

Activity of the corpora allata in the adult female migratory locust

Juvenile hormone was detected in the haemolymph of adult female Locusta by a modified Galleria bioassay. The hormone was present in the haemolymph immediately after the final ecdysis, but could not be detected after this time until the end of the period of somatic growth just before the start of ovarian development. During the first gonotrophic cycle the levels of juvenile hormone in the haemolymph could be related to the growth of the proximal oöcytes. The volumes of the corpora allata could be related to haemolymph juvenile hormone levels during the first gonotrophic cycle. Ovariectomy had no effect on haemolymph juvenile hormone levels or on the volumes of the corpora allata.     

Role of juvenile hormone in regulating tyrosine glucoside synthesis for pupal tanning in Manduca sexta (L.)

Tyrosine glucoside (α-d-glucopyranosyl-O-l-tyrosine) serves as a reservoir of tyrosine and glucose for pupal and adult cuticle formation, tanning, and pigmentation in several Lepidopteran insects. In the tobacco hornworm, Manduca sexta (L.), detectable quantities appear in the haemolymph 1–2 days after ecdysis of the fifth instar and very high concentrations accumulate between the fourth and eighth days of the stadium. If juvenile hormone II or a mimic (methoprene) is injected into fifth-instar larvae at 24-h intervals after ecdysis, tyrosine glucoside synthesis is almost completely suppressed. Temporary starvation of newly ecdysed larvae that results in the maintenance of a high endogenous juvenile hormone titre, also suppresses and delays the onset of tyrosine glucoside synthesis. The decrease and eventual disappearance of juvenile hormone after ecdysis of the last-larval instar appears to be a necessary prerequisite for the synthesis or activation of tyrosine glucoside synthetase along with the initiation of other metamorphic events.     

Inhibition of the corpora allata of last-instar male larvae of the cockroach, Diploptera punctata

Normal rates of juvenile hormone synthesis, cell number and volume of corpora allata were measured in penultimate and final-instar male larvae of Diploptera punctata. The rate of juvenile hormone synthesis per corpus allatum cell was highest on the 4th day of the penultimate stadium, declined slowly for the remainder of that stadium, and rapidly after the first day of the final stadium.Regulation of the corpora allata in final-instar males was studied by experimental manipulation of the corpora allata followed by in vitro radiochemical assay of juvenile hormone synthesis. Nervous inhibition of the corpora allata during the final stadium is suggested by the observation that rates of juvenile hormone synthesis increased following denervation of the corpora allata at the start of the stadium; this operation induced a supernumerary larval instar. Juvenile hormone synthesis by corpora allata denervated at progressively later ages in the final stadium and assayed after 4 days decreased with age at operation. This suggests an increasingly unfavourable humoral environment in the final stadium, which was confirmed by the low rate of juvenile hormone synthesis of adult female corpora allata implanted into final-instar larvae. Thus, inhibitory factors or lack of stimulatory factors in the haemolymph may act with neural inhibition to suppress juvenile hormone synthesis in final-instar males.     

Bursicon and the metabolism of tyrosine in the moulting cycle of Pieris larvae

In fourth instar larvae of Pieris brassicae the haemolymph tyrosine level begins to rise about 1 day before apolysis to reach a level about treble that in the middle of the instar. Between apolysis and ecdysis the haemolymph tyrosine level appears to decline, until just before ecdysis another steep rise occurs. About 30 min after ecdysis a steep decline starts, levelling off gradually until the level in the middle of the instar is restored.Bursicon assays show that this hormone operates in the haemolymph both during apolysis and after ecdysis; but during the actual ecdysis no bursicon activity can be demonstrated in the haemolymph.Indications have been found that the bursicon activity can restore itself spontaneously in the haemolymph of newly ecdysed larvae. This would suggest that during ecdysis a bursicon inhibitor of restricted life is operating.     

Maturation of locust corpora allata during the reproductive cycle: Effect of reserpine on allatotropic activity,juvenile hormone-III biosynthesis,and oocyte development

Reserpine, at doses of 20–175 μg per g body weight, severely retards oogenesis in newly emerged adult female migratory locusts (Locusta migratoria migratorioides) but does not increase mortality during the first 9 days and only slightly delays somatic growth. Total protein, and hemolymph vitellogenin content particularly, are significantly reduced in reserpine-treated locusts. The synthesis of juvenile hormone III (JH-III) following adult emergence, essential for induction of vitellogenesis and subsequent oogenesis, is dependent on the maturation and activation of the corpora allata (CA). CA of 7- to 8-day-old female locusts, treated with reserpine at day 1 after adult emergence, are only marginally active in vitro and are only slightly stimulated by an allatotropic factor. The basal activity and response of CA from the reserpine-treated locusts resembles that of newly emerged locusts, suggesting that reserpine specifically retards the initial maturation of the locust CA. Recovery of basal CA activity is evident on days 12–13 in reserpine-treated locusts, but responsiveness to the allatotropic factor is not recovered. Starvation of newly emerged females for 3 days and subsequent feeding did not effect ooctye development or CA activity. Cerebral content of the allatotropic factor, assayed on days 7–8, is not reduced by the reserpine treatment.