Endogenous Juvenile Hormone Titer Research Articles

Mosquitocidal activity of penfluridol as juvenile hormone antagonist

Juvenile hormone antagonists (JHANs) are known to interfere with the formation of juvenile hormone (JH) receptor complex. JHANs might be effective for control of target pests in larval stages at which stages high level of endogenous JH titer is maintained. In order to identify novel insecticidal compounds, 2352 compounds were surveyed on their JHAN activities using the yeast-two hybrid system. Among 53 compounds with JHAN activities, penfluridol showed high level of insecticidal activity against larvae of Aedes albopictus. JHAN activity was increased in proportion to the concentration of penfluridol. Larvicidal activity of penfluridol was 1.3–2.0 folds higher than that of pyriproxyfen. These results suggested that penfluridol could be useful for control of mosquito larvae.

Expressions of juvenile hormone biosynthetic genes during presoldier differentiation in the incipient colony of Zootermopsis nevadensis (Isoptera: Archotermopsidae)

Soldier differentiations require high juvenile hormone (JH) titers in workers and two molts via a presoldier stage. However, it is still unclear when the endogenous JH titer increases in workers, because identifying an individual before it undergoes the presoldier molt is quite difficult in natural conditions. In an incipient colony of Zootermopsis nevadensis Hagen, the oldest 3rd instar larva (Νo. 1 larva) always differentiates into a presoldier and the second 3rd instar larva (Νo. 2 larva) molts into a 4th instar larva. Consequently, by focusing on the ontogeny of the Νo. 1 larva, the timing of the increase in the JH titer can be determined. Here, we compared the expression levels of JH biosynthetic genes in the heads of Νo. 1 and Νo. 2 larvae. Most genes involved in JH biosynthesis were found in a genome database, and two candidate JH epoxidase (CYP15A1) genes were identified. Expression levels of JH acid methyltransferase (JHAMT) and one candidate CYP15A1, probably involved in the final steps of the JH biosynthesis, were specifically high in Νo. 1 larvae at 2–3 and 4–5 days after the appearance, respectively. Expression patterns of these genes may be used for the prediction of endogenous JH titer changes during presoldier differentiation.

Identification of a developmentally and hormonally regulated Delta-Class glutathione S-transferase in rice moth Corcyra cephalonica

Glutathione S-transferases (GSTs) are a large family of multifunctional enzymes, known for their role in cellular detoxification. Here we report a cytosolic GST with optimal activity at alkaline pH (8.3) from the visceral fat body of late-last instar (LLI) larvae of a lepidopteran insect rice moth Corcyra cephalonica. All previously known GSTs are active between pH 6.0 to 6.5. Purification and characterization revealed the Corcyra cephalonica GST (CcGST) as a 23-kDa protein. HPLC and 2D analysis showed a single isoform of the protein in the LLI visceral fat body. Degenerate primer based method identified a 701-nucleotide cDNA and the longest open reading frame contained 216 amino acids. Multiple sequence and structural alignment showed close similarity with delta-class GSTs. CcGST is present mainly in the fat body with highest activity at the late-last instar larval stage. Juvenile hormone (JH) negatively inhibits the CcGST activity both ex vivo and in vivo. We speculate that high expression and activity of CcGST in the fat body of the late-last instar larvae, when endogenous JH titer is low may have role in the insect post-embryonic development unrelated to their previously known function.

Cuticular hydrocarbons correlate with fertility, not dominance, in a paper wasp, Polistes dominulus

Cuticular hydrocarbons (CHCs) are information-rich signals in social insects that coordinate behaviors within nests. However, in some taxa, the precise information conveyed by CHCs is poorly understood. In particular, there is a debate over whether CHCs convey information about their bearer's dominance or fertility. Distinguishing between dominance and fertility signaling is difficult because fertility and rank are frequently correlated within social insect colonies. This study disentangles those relationships by examining CHCs of Polistes dominulus paper wasps during the early nest-founding stage before dominance and fertility become correlated. First, we confirm that dominance and fertility are not associated in early spring foundresses. Then we show that CHCs are more strongly associated with fertility than dominance. There was no relationship between cuticular hydrocarbon profiles and a wasp’s ability to dominate rivals through aggression, suggesting that CHCs are unlikely to provide information about dominance. However, there was a significant correlation between ovarian development and the CHC profile, suggesting that CHCs could convey valuable information about their bearer's fertility. Furthermore, our data provide a potential mechanism for chemical signaling of fecundity, as there is a relationship between endogenous juvenile hormone titer (a gonadotropin), degree of ovarian development, and the CHC profile. Hormonal regulation of CHC profile expression offers a physiological mechanism to coordinate behavior, physical state, and signal expression.

Effects of juvenile hormone III on morphogenetic changes during a molt from each nymphal instar in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Termite castes are defined by their specific characteristics. It is said that juvenile hormone (JH) plays an important role in caste differentiation and JH has been shown to highly influence imaginal-organ development, as well as soldier-specific morphogenesis in some species. To provide additional comparative data for interpreting the effects of JH on the development of alate and soldier characteristics, we performed morphological investigations on newly molted individuals from different nymphal instars of Reticulitermes speratus induced by various concentrations of JH III. As a result, each organ (especially wing (-bud) and mandible) development was shown to be strongly affected by JH III in each nymphal instar. Moreover, depending on the JH III concentration, there was a trade-off-like relationship between wing formation (alate character) and mandibular elongation (soldier character) only in molted individuals from final instar nymphs. Our results suggest that the endogenous JH titer or the threshold titer for caste-specific morphogenesis changes via nymphal development in R. speratus. This study shows that highly developmental plasticity is retained in the derived species of termites, and that it must be a driving force of caste evolution.

Sugar feedingviatrehalose haemolymph concentration affects sex pheromone production in matedHeliothis virescensmoths

Long-distance, female-produced sex pheromones are widespread among moths. Larval feeding provides most of the nutrients for development of these insects but is not thought to influence the de novo production of the fatty-acid derived compounds used as pheromones by most species. Feeding on plant nectar (sugar) by adult moths is important for increasing female fitness and also for the pollination of many plant species. In this paper, I show that feeding on sucrose solution, as opposed to water, increases sex pheromone titre in mated, but not virgin, female Heliothis virescens. Mating caused a rapid decrease in haemolymph trehalose concentration, which was restored to near-virgin levels by sugar ingestion. When isolated mated female abdomens were cultured with different concentrations of trehalose, pheromone titre increased with increasing trehalose concentration. This effect was not observed when abdomens were cultured on saline containing the sugar rhamnose, which insects cannot metabolise to glucose. Virgins injected with the juvenile hormone (JH) analogue, methoprene, showed the same effects as mated females with respect to pheromone titre and haemolymph trehalose concentration. Thus, following mating increases in JH titre increase demand for, and lowering of, blood sugar to develop oocytes, which can be compensated for by sugar ingestion. Haemolymph trehalose concentration probably influences glycolysis in gland cells and, consequently, levels of cytosolic citrate and acetyl-CoA for pheromone biosynthesis. This increase in pheromone titre in sugar-fed, mated females may facilitate further mating and increased fecundity. Thus, exogenous sugar feeding is behaviourally and physiologically integrated with endogenous JH titre to maximise female fitness.

Social reversal of immunosenescence in honey bee workers

A striking example of immunosenescence is seen in the honey bee ( Apis mellifera) worker caste. The bees' age-associated transition from hive duties to more risky foraging activities is linked to a dramatic decline in immunity. Explicitly, it has been shown that an increase in the juvenile hormone (JH) level, which accompanies onset of foraging behavior, induces extensive hemocyte death through nuclear pycnosis. Here, we demonstrate that foragers that are forced to revert to hive-tasks show reversal of immunosenescence, i.e. a recovery of immunity with age. This recovery, which is triggered by a social manipulation, is accompanied by a drop in the endogenous JH titer and an increase in the hemolymph vitellogenin level. Vitellogenin is a zinc binding glycolipoprotein that has been implicated in the regulation of honey bee immune integrity. We also establish that worker immunosenescence is mediated by apoptosis, corroborating that reversal of immunosenescence emerges through proliferation of new cells. The results presented here, consequently, reveal a unique flexibility in honey bee immunity—a regulatory plasticity that may be of general biological interest.

A Biochemical Evidence of the Inhibitory Effect of Diflubenzuron on the Metamorphosis of the Silkworm, Bombyx mori

Diflubenzuron (DFB) has been known to prevent metamorphosis of silkworm, Bombyx mori, from larval to pupal stage at low dose exposure. To explain this inhibitory action of DFB, a hypothesis was raised that DFB acts like juvenile hormone (JH) or DFB inhibits JH esterase to increase endogenous JH titer. A JH bioassay using isolated abdomen clearly indicates that DFB does not act as JH analog because DFB did not induce vitellogenesis in the isolated female abdomen, while endogenous JHs did significantly. General esterase activities in hemolymph were lower in DFB-treated fifth instar larvae than in the control larvae, but there was no difference between fat body esterase activities in both groups. Two hemolymph esterases (‘E1’ and ‘E2’) of the fifth instar larvae were separated and visualized by α-and β-naphthyl acetate. From in vitro incubation experiment, the cathodal esterase (‘E1’) was sensitive to DFB at its nanomolar range. Considering the fact that early fifth instar larvae have high level of JH esterase in the hemolymph, these results suggest that DFB inhibit larval to pupal metamorphosis by blocking JH degradation, which increases endogenous JH titer especially at the critical period when the larvae determine metamorphic development at the following molt.

Acceleration of Pupal-Adult Development by Fenoxycarb in the Silkworm, Bombyx mori

Treatment by fenoxycarb (> 0.1 μg/animal) during a short developmental period in the pharate pupal stage of the silkworm, Bombyx mori, induced alterations in the normal pupal-adult development. All fenoxycarb-treated animals showed accelerated development and precocious adult cuticle deposition very early in the pupal stage. Various internal and external organs of the developing adults underwent abnormal differentiation and were extensively malformed. Consequently, pupal-adult development and adult eclosion behaviour were disturbed. Similar effects were induced by injections of high doses (≥ 4 μg/animal) of 20-hydroxyecdysone (20E) only around the time of pupal ecdysis. Treatment with 1 μg of fenoxycarb in the pharate pupal stage did not affect haemolymph ecdysteroid titers early in the pupal stage. Our results, therefore, suggest that fenoxycarb, a potent juvenile hormone mimic, can imitate the developmental effects of excess 20E and behave as an ecdysteroid mimic after its application during the short developmental period of the pharate pupal stage of B. mori. These results shed light on the timely and coordinated increase of endogenous juvenile hormone titer before pupal ecdysis.

The juvenile hormone titer of Trichoplusia ni and its potential role in embryogenesis of the polyembryonic wasp CopidosomaFloridanum

The hemolymph juvenile hormone (JH) titer of third through fifth stadia Trichoplusia ni parasitized by the polyembryonic parasitoid, Copidosoma floridanum, was measured by radioimmunoassay and compared to the titers of unparasitized larvae. The JH titer of parasitized larvae fluctuated from 28 pg/μl to undetectable levels. Maximum levels of hormone were present at ecdysis to the fourth and fifth stadium, and at the prepupal stage. Qualitatively, similar fluctuations were observed in unparasitized larvae. However, the titers in unparasitized larvae were much lower than those of parasitized larvae in the third and early fourth stadia, and the titer fell to undetectable levels in the fifth stadium 24 h earlier (48 h) than in parasitized larvae (72 h). Preventing the JH titer from falling during the fourth and fifth stadia by topical application of ( RS)-methoprene or JH II had a juvenilizing effect on parasitized T. ni, and inhibited C. floridanum embryo morphogenesis. The effect of exogenous methoprene and JH on C. floridanum development depended on timing of application and dosage. Application of 100 pmol per day of methoprene beginning at 2 h of the host fourth stadium, prior to the large drop in the endogenous JH titer, inhibited morphogenesis in the majority of C. floridanum embryos. Application of methoprene at later times of host development did not inhibit morphogenesis although other developmental alterations were observed. The potential significance of host JH and ecdysteroid titers on polyembryonic development are discussed.

The role of the corpora allata and associated nerves in the regulation of ovarian cycles in the oviparous cockroach Periplaneta americana

Sexually mature females of the oviparous cockroach P. americana take an average of 4.17 days to complete each gonotrophic cycle. Neither sham operations on the corpora allata nor surgical sectioning of the paired nervi corporis allati I (NCA-1) or II (NCA-2) had any obvious effect on this mean cycle length. Total denervation of the corpora allata did bring about a slight lengthening of the mean cycle duration (to 5.04±0.30 days) but each of these operated insects was able nevertheless to produce at least five successive oöthecae. Surgical removal of a single corpus allatum (unilateral allatectomy) was likewise seen to slow down the rate of oötheca production. The mean cycle duration in these insects being 5.21±0.10 days. Total allatectomy abolished oötheca production completely. Measurements of juvenile hormone biosynthesis by freshly isolated corpora allata indicate that a single corpus allatum can compensate for the absence of its missing partner. Parallel experiments reveal that totally denervated corpora allata retain the ability to synthesise juvenile hormone for a considerable time after surgery. A single topical dose (100 μg) of the non-terpenoid juvenile hormone analogue fenoxycarb, in conjunction with a diet impregnated with the same compound at 10 or 100 ppm, was easily sufficient to restore oötheca production in long-term allatectomized females. The mean cycle duration in these replacement-therapy insects was 3.25±0.19 days which was significantly shorter than the interval between successive oöthecae in the control group. Topical application and feeding of fenoxycarb to otherwise intact females greatly enhanced the speed at which gonotrophic cycles were completed. The mean cycle length in this latter group was 2.69±0.05 days. It appears that the corpora allata of P. americana have a considerable capacity to function in the absence of nervous connections. Surgical operations which may reduce endogenous juvenile hormone titre have the effect of merely slowing down the maturation of oöcytes. They do not abolish the process altogether. In contrast to this an artificial elevation of juvenoid titre greatly enhances the rate of oötheca production.. Multiple gonotrophic cycles can even be induced in the total absence of fluctuating titres of endogenous juvenile hormone. It seems conceivable, therefore, that neither the build-up phase nor fall-off phase of corpus allatum biosynthetic activity are the important regulatory signals in the induction and modulation of vitellogenesis in successive batches of oöcytes in P. americana. It is rather as though the corpora allata are acting instead like a variable throttle which serves either to speed up or to slow down an endogenous “clock-like” system. This they do by merely altering the total amount of juvenile hormone which is produced over a somewhat longer period. The more hormone there is available the faster will be the process of oöcyte maturation.

Vitellogenin synthesis and secretion in crickets, Gryllus bimaculatus

1. 1. In vivo vitellogenin (vg) synthesis and secretion was measured in adult female Gryllus bimaculatus by short-term incorporation of labelled amino acids. 2. 2. Thirty min after injection of a [ 3H]amino acid mixture, high amounts of radiolabelled vgs were detected in fat body and hemolymph, and small amounts in the ovaries. A maximum in labelled hemolymph vg was found 2–3 hr after radiolabelling. 3. 3. Vitellogenin synthesis and secretion are temperature-dependent. Peak values were always obtained at the beginning of the oviposition period. 4. 4. Enforced virginity and ovariectomy did not significantly affect the incorporation of radiolabel into fat body and hemolymph vitellogenins. 5. 5. Repeated applications of 5 μg juvenile hormone (JH) III to females with a low endogenous JH titer (from 20°C.) resulted in an acceleration of vg synthesis/secretion.

Activity of optical and geometrical isomers of the juvenile hormone analogue hydroprene on endogenous juvenile hormone levels in Larval Manduca sexta

AbstractThe geometrical and optical isomers of the insect juvenile hormone analogue hydroprene (ethyl (2E,4E)‐3,7,11‐trimethyldodeca‐2,4‐dienoate) were tested in vivo, both for ability to depress endogenous juvenile hormone titre and as juvenile hormone agents in larval Manduca sexta. The structure‐activity relationships of these isomers were found to be similar both for feedback inhibition of juvenile hormone levels, and for juvenile hormone activity as indicated by pigmentation changes in larval cuticle. In both cases, the (7S) (2E,4E) isomer was the most active of the materials tested.

Endocrine manipulations, juvenile hormone and ontogenesis of male sexual behaviour in locusts

By injection of azadirachtin (AZA) to 5th instar hoppers of Locusta migratoria migratorioides, “over-aged” nymphs were produced, some of which survived for long periods without moulting to adults. Such over-aged male nymphs exhibited mating behaviour belatedly, though at a lower intensity than normal adults. Juvenile hormone (JH) markedly intensifies male sexual behaviour in crowded adult (6th instar) Locusta; thus, the lower intensity of sexual behaviour of the over-aged nymphs might have been caused by a low endogenous JH titre, or by a weaker response to the hormone. To clarify this point, chemically allatectomized over-aged 5th instar nymphs were produced by combined treatment with precocene and AZA. These exhibited a very low intensity of mating behaviour. Injections of exogenous JH III intensified the mating behaviour of the chemically allatectomized over-aged 5th instar male nymphs in a dose-dependent way, but the effect was weaker than in chemically allatectomized adult males. AZA-induced over-aged 4th instar male Locusta hoppers also exhibited mating behaviour. By injection of AZA, 5th instar over-aged hoppers of Schistocerca gregaria were also produced. Males showed mating behaviour belatedly, despite the fact that JH completely controls male sexual behaviour in this species. The intensity of this behaviour was again lower than in adults. Interrelations between integumental morphogenesis, “ethogenesis” of male sexual behaviour, and endocrine factors in locusts are discussed.

Relationship between juvenile hormone and ecdysteroids in larval-pupal development of Trichoplusia ni (Lepidoptera: Noctuiidae)

The haemolymph ecdysteroid titre during the late last stadium of the cabbage looper moth, Trichoplusia ni, was monitored in the presence of experimentally altered juvenile hormone levels to test the hypothesis that the appearance of a prepupal burst of juvenile hormone enhances prothoracic gland activity. Two peaks of ecdysteroid activity were detected in the haemolymph of last-stadium larvae (55 ng/ml and 950 ng/ml) with 20-hydroxyecdysone the most prevalent ecdysteroid. Treatment of post-feeding late last-stadium larvae with juvenile hormone I or the juvenoids, methoprene or epofenonane, had no significant effect on the timing or character of pupation. Application of juvenile hormone I to neck-ligated late last-stadium larvae failed to restore peak ecdysteroid levels to those of unligated controls. Application of the anti-juvenile hormone compounds, fluoromevalonolactone or 3,3-dichloro-2-propenyl hexanoate, disrupted metamorphosis causing delays in tanning and the formation of abnormal pupae. Yet, corresponding deviations in the timing or magnitude of ecdysteroid levels or in the conversion of ecdysone to 20-hydroxyecdysone were not observed. When early last-stadium larvae were treated with the juvenile hormone esterase inhibitor, 3-octylthio-1,1,1-trifluoro-2-propanone, shifts in the timing of peak ecdysteroid levels, coincident with delayed pupation, were observed. These results suggest that the prepupal prothoracic glands of T. ni may be considerably less sensitive to changes in the endogenous juvenile hormone titre by the time larvae have begun to wander, even though treatment at this time may still produce toxic effects that influence the success of ecdysis and/or resultant pupal morphology.

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.

Precocene-induced effects and possible role of juvenile hormone during embryogenesis of the milkweed bug Oncopeltus fasciatus

Precocene 2 was used as a tool for uncovering possible juvenile hormone functions during embryogenesis of the milkweed bug Oncopeltus fasciatus. The most conspicuous effect, which was observed after precocene treatment of freshly laid eggs, was the secondary dorsal closure defect (DC-defect). In these embryos growth processes of the ectoderm leading to dorsal closure were disturbed, i.e., the ectoderm (resp. epidermis) failed to replace the amnion in the abdominal dorsum. The critical period for triggering the DC-defect is around 72 hr, a few hours after blastokinesis. This is the time when the endogenous juvenile hormone titer rises and the fine structure of the corpus allatum indicates a synthetic activity in nontreated embryos ( A. Dorn, 1975, Verh. Deutsch. Zool. Ges, 67, 85–89). Thus. also during embryogenesis an antiallatotropic action of precocene 2 seems probable. The fact that the DC-defect can be overcome when precocene treatment is followed by application of juvenile hormone 1 supports this assumption. On the grounds of the described experiments it is suggested that endogenous juvenile hormone controls ectodermal (resp. epidermal) growth processes leading to secondary dorsal closure.