Rates Of Juvenile Hormone Synthesis Research Articles

Ovarian stimulation of juvenile hormone biosynthesis in the viviparous cockroach, Diploptera punctata

A direct radiochemical assay for juvenile hormone (JH) biosynthesis by the corpora allata (CA) showed that the cyclic changes in biosynthesis associated with the gonadotrophic cycle were abolished in the absence of ovaries whether or not the CA were innervated. In ovariectomized animals denervated CA synthesized JH at slightly higher rates than did innervated CA. However, the low rates of JH synthesis in ovariectomized females were sufficient to result in accumulation of vitellogenin in the hemolymph to levels twice those of normal females. Implantation of one ovary 1 week after ovariectomy resulted in a cycle of JH biosynthesis qualitatively similar to that observed during a normal gonadotrophic cycle. Implantation of one ovariole did not result in a detectable cycle of JH biosynthesis whereas normal rates of JH synthesis were observed after implantation of three or six ovarioles. Implantation of four ovaries resulted in a cycle of CA activity more attenuated than that observed in the presence of one ovary. Nonetheless all four ovaries sequestered a normal quantity of vitellin.

Effects of decapitation and ovariectomy on the regulation of juvenile hormone synthesis in the cockroach, Diploptera punctata

Corpora allata from Diploptera punctata females at adult ecdysis or at the end of the last-larval stadium, when implanted into decapitated females, underwent a cycle of juvenile hormone synthesis similar in timing and magnitude to that of glands implanted into control animals which had been starved and allatectomized. Starvation did not alter the cycle in rates of juvenile hormone synthesis of sham-operated animals. Decapitation of ovariectomized animals resulted in no cycle in rates of juvenile hormone synthesis by implanted adult corpora allata; however, implantation of an ovary along with the corpora allata into decapitated, ovariectomized hosts resulted in a cycle of juvenile hormone synthesis. In control animals, which retained their heads but were starved and allatectomized as well as ovariectomized, the implanted corpora allata showed a cycle of juvenile hormone synthesis only when implanted with an ovary. The maximal rates of juvenile hormone synthesis by the corpora allata in both experimental and control conditions were lower than normal, likely due to the repeated trauma of surgery. However, at no time from eclosion to the end of the first gonotrophic period was the brain necessary for the cyclic response of the corpora allata to the presence of the ovary.

Influence of temperature and carbon dioxide concentration on juvenile hormone titre and dependent parameters of adult worker honey bees ( Apis mellifera L.)

It is known that juvenile hormone plays an important role in the regulation of labour division and of the different life spans, and that the microclimate of the bee hive is characterized by its high CO 2 concentration and its varying temperature depending on the presence of brood. We have investigated the influence of microclimates characteristic of breeding and broodless areas on the juvenile hormone titre in the haemolymph and whole body extracts, on the corpora allata in vitro activity, on the degradation of juvenile hormone and on the dry weight of the hypopharyngeal glands using bees of known ages. A microclimate of 35°C and 1.5% CO 2, as observed in the breeding area, induces a rapid and pronounced increase in the juvenile hormone titre. On the other hand, this titre remains low in bees kept at 27°C and 1.5% CO 2, a microclimate associated with broodless combs. Rates of juvenile hormone synthesis by corpora allata in vitro were found to be extremely low, even in the presence of farnesenic acid, and not related to the juvenile hormone titre. In vitro incubation of juvenile hormone in haemolymph revealed no degradation while injected juvenile hormone was found to be degraded and taken up by the gut at rates only weakly correlated with the juvenile hormone titre. We propose a hypothetical model for the regulation of the juvenile hormone titre as well as the course of labour division by the varying microclimates observed in the bee hive.

Increased juvenile hormone synthesis and decreased fertility in aging Schistocerca gregaria

The fertility of aging Schistocerca gregaria females of both solitary and gregarious phases is markedly reduced in comparison with that of young females. Examination of eggs (from both young and aging females) maintained in vitro revealed that the decreased fertility of aging females of both phases could be attributed to a decrease in viability of eggs. This, in turn, was found to be in large part due to an increase in the proportion of embryos showing inhibited development. The proportion of inhibited embryos, in pods from young and old females, respectively, increased from 5 to 42% for gregarious animals and from 3 to 38% for solitary animals. Inhibition was found to occur at all stages from blastokinesis to ecdysis of the provisional cuticle. These morphogenetic aberrations were very similar to those obtained after treatment of S. gregaria eggs with exogenous juvenile hormone (JH). Investigation of the JH synthetic activity of corpora allata from aging females of each phase revealed a marked increase in the rates of JH synthesis in comparison with those of young females of the same phase. Furthermore, injection of JH into young females increased the proportion of embryos showing inhibited development from 7% (in control females) to 30% (in JH-treated females). These results suggest a possible correlation between reduced viability of eggs and high rates of JH synthesis in aging S. gregaria of both phases.

Control of the Corpora Allata During a Reproductive Cycle in a Viviparous Cockroach

SYNOPSIS. This paper describes factors which regulate the corpora allata (CA) during the reproductive cycle in the viviparous cockroach Diploptera punctata . Experiments, designed to alter the rate of juvenile hormone (JH) synthesis by the CA, are performed on whole animals and their effects are demonstrated by an in vitro radiochemical assay for JH synthesis by the CA. The CA is both inhibited and stimulated. Axonal pathways from the brain to the CA are required for inhibition of the CA in virgin females but not in young pregnant females. Humorally transmitted inhibition of the CA is caused in vivo by JH (in high titers) and ecdysteroid hormone. JH in low titers also stimulates the CA. Since these hormones do not affect the CA in vitro we suggest that they exert their effect via the central nervous system. The ovary, a possible source of ecdysteroids in the hemolymph, is necessary both for maintenance of JH synthesis and for inhibition in the rate of JH synthesis at the end of egg growth.

The mechanism of compensation in juvenile hormone synthesis following unilateral allatectomy in Diploptera punctata

Following unilateral allatectomy in the viviparous cockroach, Diploptera punctata, the remaining corpus allatum (CA) can synthesize juvenile hormone (JH) at rates equal to that of a pair of control CA. A single CA undergoes changes in volume and cell number similar in magnitude to those occurring during the normal cycle of JH synthesis. There is no hyptertrophy of the CA associated with compensation in JH synthesis. Therefore, the rate of JH synthesis per cell or per unit volume of single CA following unilateral allatectomy is twice that of a single control CA.

Cellular and volumetric changes in relation to the activity cycle in the corpora allata of Diploptera punctata

In the corpora allata (CA) of the viviparous cockroach, Diploptera punctata, a cycle of juvenile hormone (JH) synthesis during ovarian maturation can be correlated with cyclical changes in CA volumes and cell numbers. Uptake of [ 3H]-thymidine occurs in nuclei of CA cells during periods of increase in cell number. Both members of a pair of CA maintain symmetry of volume, cell number and rate of JH synthesis. After a cycle of CA activity, the CA can be transplanted to a young, allatectomized female, where they support a second wave of oöcyte development.

Phase polymorphism in Schistocerca gregaria: Assessment of juvenile hormone synthesis in relation to vitellogenesis

Juvenile hormone (JH) synthesis by the corpora allata of gregarious and solitarious phase females of Schistocerca gregaria was determined in vitro during the penultimate and last stadia as well as during the first gonotrophic period of adults. Generally, the corpora allata of solitarious females showed higher rates of JH synthetic activity. In addition, in adult females there was a temporal difference between the corpora allata activities of gregarious and solitarious locusts, the latter exhibiting relatively higher rates of JH synthesis early in the first gonotrophic period. The corpus allatum volumes of solitarious females were also generally larger than those of their gregarious counterparts; there was no synchrony between fluctuations in JH synthetic activity and changes in corpus allatum volume in either phase. The early onset of relatively high JH synthetic rates in solitarious females was correlated with the early detection, by rocket immunoelectrophoresis, of vitellogenin in the haemolymph and vitellin in the oöcytes. Vitellogenin appeared in the haemolymph on day 4 in solitarious females and on day 6 in gregarious females and vitellin appeared in the oöcytes on days 6 and 8 respectively. Oöcyte length at which vitellogenesis was first detected was 1.8 mm for gregarious and 1.3 mm for solitarious females. However, despite the accelerated onset of both vitellogenin synthesis and uptake, oöcyte maturation time of solitarious females was longer. In both gregarious and solitarious females, vitellogenin titres increased until oöcytes reached a length of about 4 mm and declined thereafter. Vitellin content of ovaries increased proportionately to oöcyte growth until they attained a length of 5.0 mm. The subsequent increase in length of oöcytes to maturity is attributed to postvitellogenic growth, possibly by hydration.

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 C 16 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.

Control of juvenile hormone biosynthesis during the reproductive cycle of a viviparous cockroach II. Effects of unilateral allatectomy, implantation of supernumerary corpora allata, and ovariectomy

Using a direct radiochemical assay, the effects of implantation of supernumerary corpora allata (CA), unilateral allatectomy, and ovariectomy on rates of juvenile hormone (JH) biosynthesis by the CA and on the duration of the gonotrophic cycle have been investigated during the first gonotrophic cycle of the viviparous cockroach Diploptera punctata. Implantation of supernumerary CA decreased the duration of the gonotrophic cycle and had no effect on JH biosynthesis by denervated host CA or by implanted glands. Thus, there appears to be no evidence for a compensatory response reducing JH synthesis under these conditions of high JH titers. Unilateral allatectomy, however, resulted in compensation by the remaining CA: a single CA synthesized the same quantity of JH during the gonotrophic cycle as a pair of CA although maximum rates of synthesis were delayed by 1 day. Accordingly, the gonotrophic cycle is slightly longer in duration in unilaterally allatectomized animals. Ovariectomy either as nymphs or young adults depressed the rate of JH synthesis by the CA. A model for the regulation of JH biosynthesis by the corpora allata in cockroaches is proposed.

Control of juvenile hormone biosynthesis during the reproductive cycle of a viviparous cockroach: I. Activation and inhibition of corpora allata

An in vitro radiochemical assay has been used to determine the juvenile hormone (JH) synthetic capacity of denervated and transplanted corpora allata (CA) of female Diploptera punctata. CA maintained in vitro over a 24-hr period do not increase their rate of JH synthesis whether taken from females in which they would undergo a dramatic increase in vivo (just before vitellogenesis) or from females in which CA synthesize JH at a low rate for an extended period (as in pregnancy). However, when CA are denervated and allowed to remain in vivo, a normal cycle of JH synthesis is observed in mated females. In virgin females, which do not normally mature eggs, the denervation mimics mating in that the CA undergo a synthetic cycle and oocytes are matured. Denervation of CA of young pregnant females (16% gestation) does not result in an immediate cycle of synthesis similar to that of mated females, nor do 0-day CA transplanted to allatectomized pregnant females exhibit such a cycle. However, inactive CA from the pregnant females transplanted to allatectomized 0-day animals promptly undergo a cycle of JH synthesis with an associated maturation of oocytes. From these results it is concluded that the integrity of the nerves of CA is required for inhibition of synthetic activity, whereas some factor in the hemolymph, not present in pregnant females, is responsible for activation and maintenance of the JH synthetic cycle.

Juvenile-Hormone Esterase in Insect Development: A Comparative Study

Juvenile-hormone (JH) esterase activity is found in the hemolymph of last larval (nymphal) instars of Periplaneta brunnea, Schistocerca vaga, Samia cynthia, and Tenebrio molitor, but not in Sarcophaga bullata. In Samia cynthia larvae maximum activity coincides with the JH inactivation preceding metamorphosis; in young Hyalophora cecropia moths the increase in JHE activity coincides with a sharp rise in the rate of JH synthesis. Pupal hemolymph of T. molitor has the highest activity of any species or stage tested. The enzymes of Samia cynthia and T. molitor hydrolyze JH-1 and ethyl ester analogs, whereas the Δ²-cis isomer of JH-I and isopropyl ester analogs (only tested with T. molitor hemolymph) are unaffected.

The synthetic activity and glandular volume of the corpus allatum during ovarian maturation in the desert locust [formula omitted

We have compared, on an individual basis, the volume of the corpora allata with their ability to synthesize and release juvenile hormone (JH) using glands taken at daily intervals throughout the period of sexual maturation and the first two ovarian cycles in Schistocerca gregaria . A standard in vitro radiochemical assay was used to measure the rates of both spontaneous JH biosynthesis from [methyl- 14C]-methionine, and of JH biosynthesis stimulated by optimal concentrations of [C-2 3H]-farnesenic acid. Computation of results showed that there are, during this period, changes of up to 250-fold in the rate of spontaneous JH biosynthesis per unit volume corpora allata. It is concluded that the volume of the corpora allata is of no value as an indicator of the spontaneous synthetic activity of the glands in this species, and that the overall rate of JH synthesis is regulated by mechanisms that do not involve large changes in the volume of the gland cells. However, in the presence of farnesenic acid, there is a corelation between stimulated JH synthesis and glandular volume, suggesting that the volume of the gland reflects the maximum activity of the final two stages in JH biosynthesis.

Spontaneous synthesis and release of C 16 juvenile hormone by isolated corpora allata of female locust Schistocerca gregaria and female cockroach Periplaneta americana

Isolated pairs of corpora allata (CA) from adult females of both Schistocerca gregaria and Periplaneta americana incorporate radioactivity from [methyl- 14C] methionine into C 16 juvenile hormone (JH) when incubated for up to several hours, such that the rate of JH synthesis can be accurately determined. Analysis of the medium shows that CA from P. americana continue to release newly synthesised JH at constant rates for at least 5 hr, whereas those from S. gregaria may show a marked decrease in rate of JH release after 3 hr, particularly in the case of glands having high initial rates of synthesis and release. In both cases the rates of release of JH are strictly proportional to the rates of JH synthesis when measured over a period of 3 hr incubation, independent of the rate of synthesis. It is concluded that the spontaneous level of endocrine activity in glands from both these species can be faithfully quantified by precise radiochemical methods using the short-term incubation procedures described.

Corpus allatum activity in vitro during ovarian maturation in the desert locust, Schistocerca gregaria.

1. Radiochemical in vitro assays show that there are large and rapid changes in the spontaneous rate of juvenile hormone synthesis and release during the course of sexual maturation in the locust. 2. Parallel observations on glands incubated with farnesenic acid show that the rate-limiting step is always prior to the stage of esterification of farnesenic acid to the final intermediate, methyl farnesoate. 3. Corresponding changes in oocyte morphometrics do not reveal any clear correlation between endocrine activity of the corpus allatum and either the induction or maintenance of rapid vitellogenesis. 4. Peaks of synthetic activity in the corpus allatum correspond well with the onset of previtellogenic growth in the oocytes. 5. The data do not provide any evidence that 'corpus allatum insufficiency' is responsible for resorption of growing oocytes. 6. It is concluded that short-term in vitro radio-assays provide a valid method for estimating quantitatively the physiological activity of the corpus allatum.