Regulation Of Juvenile Hormone Titer Research Articles

Quercetin stimulates an accelerated burst of oviposition-based reproductive strategy in codling moth controlled by juvenile hormone signaling pathway

The advantageous characteristics of invasive pests, particularly their ability to reproduce and adapt to the environment, have been observed. However, it remains unclear what specific inherent superiority enables fruit pests to successfully invade and dominate in interactions with other species. In this study, we report that Cydia pomonella (Linnaeus), a notorious invasive pest of pome fruits and walnuts globally, employs unique reproductive strategies in response to quercetin, a plant compound in host fruits. By monitoring adult dynamics and fruit infestation rates, we observed a competitive relationship between C. pomonella and the native species Grapholita molesta (Busck). C. pomonella was able to occupy vacant niches to ensure its population growth. We also found that quercetin had different effects on the reproductive capacity and population growth of C. pomonella and G. molesta. While quercetin stimulated the fecundity and population growth of G. molesta, it inhibited C. pomonella. However, C. pomonella was able to rapidly increase its population after exposure to quercetin by adopting an ‘accelerated burst’ of oviposition strategy, with each individual making a greater reproductive contribution compared to the control. We further demonstrated that the effect of quercetin on oviposition is regulated by the juvenile hormone (JH) signaling pathway in C. pomonella, allowing it to prioritize survival. The enhanced reproductive fitness of G. molesta in response to quercetin is attributed to the regulation of JH titers and key genes such as Met and Kr-h1, which in turn up-regulate reproduction-related genes Vg and VgR. In contrast, C. pomonella is inhibited. These findings shed light on the mechanisms interspecific competition and help to improve our understanding of the global spread of C. pomonella, which can be attributed to its inherent superiority in terms of reproductive strategy.

Expression and characterization of recombinant Juvenile Hormone Epoxide Hydrolase of Spilarctia obliqua, a major pest in Agri-Sericulture

Juvenile Hormone (JH) modulates a variety of developmental and physiological processes in Insects. Previous studies suggest that the two hydrolytic enzymes namely Juvenile Hormone Esterase (JHE) and Juvenile Hormone Epoxide Hydrolase (JHEH) play important roles in the regulation of JH titer. Compared with JHE, JHEH is more essential regulatory enzyme and could be applied to control insects, because of its irreversible reaction on JH Mechanism. A full length of cDNA (1323bp) encoding juvenile hormone epoxide hydrolase gene from Spilarctia obliqua (SoJHEH) is isolated and subcloned into baculovirus vector system using pFastBac and pFastBac-HTA vectors. The bacmid-transformed SoJHEH is expressed in Insect cell line system and the expression of recombinant SoJHEH is confirmed by Western blotting. The enzyme activity of recombinant SoJHEH showed a high activity with JH III and very low with other general epoxide substrates. The deduced SoJHEH protein sequence showed the conserved domains of catalytic triad and oxyanion hole indicating the well preserved catalytic mechanism of epoxide hydration which can be explored further for bio control strategy at molecular level using insect’s own enzyme which can address the current problem of insect resistance.

Involvement of a putative allatostatin in regulation of juvenile hormone titer and the larval development in Leptinotarsa decemlineata (Say)

Juvenile hormone III (JH III) plays primary roles in regulation of metamorphosis, reproduction and diapause in Leptinotarsa decemlineata, a notorious defoliator of potato. The neurosecretory cell-borne substance(s) negatively affects the final two steps in JH biosynthesis, catalyzed respectively by an epoxidase CYP15A1 and a juvenile hormone acid methyltransferase (JHAMT). In a few insect species other than L. decemlineata, the inhibitory substance is allatostatin (AS) neuropeptide. In this study, two putative AS genes encoding LdAS-C and LdAS-B precursors were cloned. Both LdAS-C and LdAS-B were expressed in the egg, larvae, pupae and adults, and highly expressed in the brain and the gut. Dietary introduction of double-stranded RNAs (dsRNAs) targeting LdAS-C and LdAS-B successfully knocked down respective target genes. Ingestion during 3 and 6 consecutive days of dsLdAS-C significantly increased the LdJHAMT mRNA levels by 3.8 and 9.9 fold respectively. In contrast, ingestion of dsLdAS-B only slightly increased the LdJHAMT expression level by 1.1 and 1.7 fold. Moreover, after one, two and three days' ingestion of dsLdAS-C, the relative JH levels in the hemolymph of treated larvae were 2.5, 4.2 and 1.9 fold higher than those in control beetles. Furthermore, ingestion of dsLdAS-C and dsLdAS-B significantly affected larval growth and delayed larval development. Thus, we provide a line of experimental evidence in L. decemlineata to support the concept that AS-C acts as an allatostatin and inhibit JH biosynthesis.

Effect on mandibular length of juvenile hormones and regulation of soldier differentiation in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

To understand the relationship between juvenile hormone (JH) titers and morphogenetic changes associated with soldier differentiation of the termite Reticulitermes speratus, mandibular length (length between apex and first teeth) of presoldiers induced by various concentrations of JH III (0–320 μg per dish) was measured. Presoldiers were observed when treated with more than 20 μg JH III. Both left and right mandibular lengths were significantly different among differentiated presoldiers treated with different concentrations of JH III. Concentration-dependent effects on mandibular lengths were observed: higher JH III concentrations (160 and 320 μg) caused differentiation in presoldiers with longer mandibles, and lower concentrations (40 and 80 μg) caused differentiation in presoldiers with shorter mandibles. These results suggest that morphogenetic changes specific to soldiers are influenced by JH titers (endogenous JH+applied JH III) in workers. Live soldiers could inhibit presoldier differentiation in R. speratus workers. Interestingly, mandibular lengths of presoldiers induced by JH III were influenced by soldier presence, which could influence morphological changes, probably by regulation of JH titers in workers, as recently shown in the termite Coptotermes formosanus.

A mathematical model for the regulation of juvenile hormone titers

The titer of juvenile hormone (JH) is determined by three factors: its rate of synthesis, its rate of degradation, and the degree to which JH is protected from degradation by binding to a diversity of JH-binding proteins. All three of these factors vary throughout the life history of an insect and contribute to variation in the JH titer. The relative importance of each of these factors in determining variation in the JH titer is not known and can, presumably, differ in different life stages and different species. Here we develop a mathematical model for JH synthesis, degradation, and sequestration that allows us to describe quantitatively how each of these contribute to the titer of total JH and free JH in the hemolymph. Our model allows for a diversity of JH-binding proteins with different dissociation constants, and also for a number of different modes of degradation and inactivation. The model can be used to analyze whether data on synthesis and degradation are compatible with the observed titer data. We use the model to analyze two data sets, from Manduca and Gryllus, and show that in both cases, the known data on synthesis and degradation cannot account for the observed JH titers because the role of JH sequestration by binding proteins is greatly underestimated, and/or the in vivo rate of JH degradation is greatly overestimated. These analyses suggest that there is a critical need to develop a better understanding of the in vivo role of synthesis, sequestration and degradation in JH titer regulation.

Molecular cloning and developmental expression of the gene encoding juvenile hormone esterase in the yellow-spotted longicorn beetle, Psacothea hilaris

Juvenile hormone (JH) plays a key role in the regulation of growth, development, diapause and reproduction in insects. The regulation of JH titers in the insect body is therefore crucial throughout postembryonic development. One of the major pathways of JH metabolism is degradation by a highly selective enzyme, juvenile hormone esterase (JHE). We obtained a full-length cDNA encoding JHE in Psacothea hilaris ( PhJHE). The complete PhJHE cDNA sequence is comprised of 1989 bp with an open reading frame of 1785 bp encoding 595 amino acid residues. The deduced protein sequence of PhJHE showed high homology with the Tenebrio molitor JHE (50% amino acid identity) and moderate homology with the Drosophila melanogaster JHE (34%). The PhJHE transcript was expressed mainly in the fat body. PhJHE transcript levels were low until day 3 of the 5th (final) larval instar, then steadily increased reaching a peak on day 13 (the prepupa stage), coinciding well with the peak hemolymph enzyme activity level. Sustained starvation of larvae after a period of feeding stimulated the expression of PhJHE mRNA while feeding the larvae with glucose downregulated its expression. These results are discussed with reference to the induction of precocious metamorphosis in this beetle by starvation.

Regulation of juvenile hormone titers by soldiers in the Formosan subterranean termite, Coptotermes formosanus

In field collections of the Formosan subterranean termite Coptotermes formosanus, soldiers averaged less than 10%. The proportion of soldiers increased to about 25% or higher when termites were kept in the laboratory, as did the juvenile hormone III (JH III) titers for both workers and soldiers. In laboratory experiments with a proportion of soldiers 25% or higher, very few new pre-soldiers were formed and the JH titer in existing soldiers remained constant. On the contrary, workers from groups containing less than 25% soldiers formed more pre-soldiers. In such cases, both workers and soldiers showed higher JH titers. Newly formed soldiers also had higher JH titers than older soldiers. It is speculated that populations containing higher soldier proportions inhibit further soldier differentiation, eventually holding the JH titers under the threshold or suppressing the activity of corpora allata resulting in lower JH titers in workers.

Feedback Regulation of Juvenile Hormone Titer by Biogenic Amines in Drosophilidae

Feedback Regulation of Juvenile Hormone Titer by Biogenic Amines in Drosophilidae

Regulation of JH titers: The relevance of degradative enzymes and binding proteins

Juvenile hormones play a crucial role in development, metamorphosis, and reproduction of insects. This mini-review discusses the nature of the juvenile hormones identified in insects and their changes in concentration in the hemolymph during development and reproduction. The hemolymph titer is largely determined by the rate at which juvenile hormones are synthesized and released by the corpora allata, but other factors are also involved in titer regulation, such as the affinity and concentration of juvenile hormone binding proteins in the hemolymph and the rate of juvenile hormone degradation in hemolymph and tissues. Juvenile hormone specific esterases occur in hemolymph and tissues, whereas epoxide hydrolases, which may degrade the hormone, are exclusively tissue bound. The activities of these degradative enzymes and the concentration of binding proteins change during the insect life cycle and these changes are related to fluctuations in hormone titer. However, we are still a long way from understanding the subtle interactions between these components in regulation of juvenile hormone titers. In particular, our knowledge is hampered by lack of information about the types, concentrations, and affinities of intracellular juvenile hormone receptors. © 1996 Wiley-Liss, Inc.

Ovaries and regulation of juvenile hormone titer in Acheta domesticus L. (Orthoptera)

A study was performed on females Acheta domesticus to examine the effects of various experimental conditions on the ovarian physiology. Using a radioimmunoassay to determine juvenile hormone (JH) titers as well as in vitro JH biosynthesis, we observed that retention of mature follicles in egg-retaining females, i.e., virgins or mated females not provided an egg-laying substrate, inhibits JH production and consequently oocyte development. Mating in intact as well as ovariectomized females does not affect corpora allata activity. It is only when mating is associated with egg laying that JH biosynthesis and hemolymph titers increased and oocyte development and fecundity are stimulated. Despite lower JH biosynthesis, ovariectomized females present enlarged corpora allata and the levels of JH observed in their hemolymph were intermediate between those of intact egg-laying and virgin females. In intact females, the hemolymph JH titers as well as the JH esterase activities were related to ovarian development. JH esterase activity was very high in ovariectomized animals. Several factors involved in ovarian development of A. domesticus are discussed.

Regulation of juvenile hormone titer in African locust

In the African locust, the titer of C-16 JH in hemolymph (determined by GC-MS), reflects the rate of hormone biosynthesis (determined by RCA) in normal adult females. Severance of the nervi corporis allati-I (NCA-I) results in a low C-16 JH biosynthesis without affecting physiological events dependent on JH. In NCA-I-transectioned animals, JH titer is higher than in control locusts. JH catabolism does not seem to be involved in this high titer of hormone associated with a very low rate of JH production. In sham-operated females, the bulk of injected [3H]C-16 JH quickly disappeared from the hemolymph but JH was retained in the bloodless body. After severance of the NCA-I, the remaining radiolabeled JH in the hemolymph increased. These results suggest the role of tissue JH-binding or of JH excretion in regulating its level in the locust.

Juvenile hormone induction of esterases: a mechanism for the regulation of juvenile hormone titer.

Within a few hours after injection of juvenile hormone into Hyalophora gloveri pupae, several fast-migrating carboxylesterases (EC 3.1.1.1) that are sensitive to diisopropylfluorophosphate appear in the hemolymph. Treatment of the pupae with puromycin or actinomycin D prevents the appearance of these hemolymph enzymes, suggesting de novo synthesis of the carboxylesterases. Of the several other compounds investigated, only a potent mimic of the juvenile hormone is able to induce these enzymes. When the induced enzymes are incubated in vitro with (14)C-labeled juvenile hormone, the hormone is rapidly and efficiently degraded. It is suggested that these induced carboxylesterases play an important role in the regulation of juvenile hormone titer.