Sensitivities to juvenile hormone and ecdysteroid in the diapause larvae of Omphisa fuscidentalis based on the hemolymph trehalose dynamics index

Comprehensive Proteomics Analysis of the Hemolymph Composition of Sugar-Fed Aedes aegypti Female and Male Mosquitoes

In arthropods, hemolymph carries immune cells and solubilizes and transports nutrients, hormones, and other molecules that are involved in diverse physiological processes including immunity, metabolism, and reproduction. However, despite such physiological importance, little is known about its composition. We applied mass spectrometry-based label-free quantification approaches to study the proteome of hemolymph perfused from sugar-fed female and male Aedes aegypti mosquitoes. A total of 1403 proteins were identified, out of which 447 of them were predicted to be extracellular. In both sexes, almost half of these extracellular proteins were predicted to be involved in defense/immune response, and their relative abundances (based on their intensity-based absolute quantification, iBAQ) were 37.9 and 33.2%, respectively. Interestingly, among them, 102 serine proteases/serine protease-homologues were identified, with almost half of them containing CLIP regulatory domains. Moreover, proteins belonging to families classically described as chemoreceptors, such as odorant-binding proteins (OBPs) and chemosensory proteins (CSPs), were also highly abundant in the hemolymph of both sexes. Our data provide a comprehensive catalogue of A. aegypti hemolymph basal protein content, revealing numerous unexplored targets for future research on mosquito physiology and disease transmission. It also provides a reference for future studies on the effect of blood meal and infection on hemolymph composition.

Functional characterization of a geranylgeranyl diphosphate synthase in the leaf beetle Monolepta hieroglyphica

Geranylgeranyl diphosphate synthase (GGPPS) as the short-chain prenyltransferases for catalyzing the formation of the acyclic precursor (E)-GGPP has been extensively investigated in mammals, plants, and microbes, but its functional plasticity is poorly understood in insect species. Here, a single GGPPS in leaf beetle Monolepta hieroglyphica, MhieGGPPS, was functionally investigated. Phylogenetic analysis showed that MhieGGPPS was clustered in one clade with homologs and had six conserved motifs. Molecular docking results indicated that binding sites of dimethylallyl diphosphate (DMAPP), (E)-geranyl pyrophosphate (GPP), and (E)-farnesyl pyrophosphate (FPP) were in the chain-length determination region of MhieGGPPS, respectively. In vitro, recombiant MhieGGPPS could catalyze the formation of (E)-geranylgeraniol against different combinations of substrates including isopentenyl pyrophosphate (IPP)/DMAPP, IPP/(E)-GPP, and IPP/(E)-FPP, suggesting that MhieGGPPS could not only use (E)-FPP but also (E)-GPP and DMAPP as the allylic cosubstrates. In kinetic analysis, the (E)-FPP was most tightly bound to MhieGGPPS than that of others. It was proposed that MhieGGPPS as a multifunctional enzyme is differentiated from the other GGPPSs in the animals and plants, which only accepted (E)-FPP as the allylic cosubstrate. These findings provide valuable insights into understanding the functional plasticity of GGPPS in M. hieroglyphica and the novel biosynthesis mechanism in the isoprenoid pathway.

Metformin-induced AMPK activation suppresses larval growth and molting probably by disrupting 20E synthesis and glycometabolism in fall webworm, Hyphantria cunea Drury

Metformin, considered to be a potent AMPK activator, is widely used for clinical therapy of cancer and diabetes due to its distinct function in regulating cell energy balance and body metabolism. However, the effect of metformin-induced AMPK activation on the growth and development of insects remains largely unknown. In the present study, we focused on the role of metformin in regulating the growth and development of Hyphantria cunea, a notorious defoliator in the forestry. Firstly, we obtained the complete coding sequences of HcAMPKα2, HcAMPKβ1, HcAMPKγ2 from H. cunea, which encoded a protein of 512, 281, and 680 amino acids respectively. Furthermore, the phylogenetic analysis revealed that these three subunits were highly homologous with the AMPK subunits from other lepidopteran species. According to the bioassay, we found metformin remarkably restrained the growth and development of H. cunea larvae, and caused molting delayed and body weight reduced. In addition, expressions of HcAMPKα2, HcAMPKβ1, and HcAMPKγ2 were upregulated 3.30-, 5.93- and 5.92-folds at 24 h after treatment, confirming that metformin activated AMPK signaling at the transcriptional level in H. cunea larvae. Conversely, the expressions of two vital Halloween genes (HcCYP306A1 and HcCYP314A1) in the 20E synthesis pathway were remarkably suppressed by metformin. Thus, we presumed that metformin delayed larval molting probably by impeding 20E synthesis in the H. cunea larvae. Finally, we found that metformin accelerated glycogen breakdown, elevated in vivo trehalose level, promoted chitin synthesis, and upregulated transcriptions of the genes in chitin synthesis pathway. Taken together, the findings provide a new insight into the molecular mechanisms by which AMPK regulates carbohydrate metabolism and chitin synthesis in insects.

The feeding status regulates the action of insulin and 20-hydroxyecdysone on haemolymph trehalose level in Bombyx larvae

Insulin in mammals is known for its effect on carbohydrate metabolism and maintenance of blood sugar levels. In the present study, we explored the effect of exogenous insulin and 20-hydroxyecdysone (20E) on carbohydrate metabolism in Bombyx mori under the fed and food-deprived conditions. The study showed that insulin and 20E regulate the trehalose (major circulating sugar) level in B. mori, and larval feeding status plays a decisive role in influencing the action of these two hormones. At feeding, both insulin and 20E showed its hypertrehalosemic action but at food deprivation, these hormones acted as hypotrehalosemic factors. Although both insulin and 20E showed the same effect on the haemolymph trehalose level either at feeding or food deprivation, the metabolic regulation was different for these two hormones. Insulin treatment to fed larvae increased the haemolymph trehalose level without altering the effectiveness of trehalose utilization but possibly by inducing the activity of glycogen phosphorylase enzyme and releasing glucose-1-P for the increased synthesis of trehalose. The treatment of 20E to fed larvae also increased the trehalose level, but concurrently it also increased both the enzyme activity of trehalase and glycogen phosphorylase. Insulin treatment to food-deprived larvae decreased the circulating trehalose level by increasing the trehalose breakdown as the mRNA expression level of trehalase-2 and enzyme activity of trehalase increased in these larvae. The treatment of 20E to food-deprived larvae decreased the haemolymph trehalose possibly by decreasing its synthesis, as glycogen phosphorylase enzyme activity decreased in these larvae, thus restricting the availability of glucose-1-P for trehalose synthesis. The study, thus suggests that both insulin and 20E regulate carbohydrate metabolism in B. mori.

Regulation of a Trehalose-Specific Facilitated Transporter (TRET) by Insulin and Adipokinetic Hormone in Rhodnius prolixus, a Vector of Chagas Disease

Using the blood-sucking kissing bug, Rhodnius prolixus as an experimental model, we have studied the involvement of insulin-like peptides (ILPs) and adipokinetic hormone (AKH) signaling in carbohydrate metabolism, focusing on the regulation of the trehalose-specific facilitated transporter (Rhopr-TRET), particularly in the ovaries. We find that trehalose stores in ovaries increase after feeding, synchronously with the beginning of vitellogenesis, but that the transcript expression of enzymes involved in trehalose synthesis show no changes between unfed and blood-fed animals. However, an eightfold increase in Rhopr-TRET transcript expression is observed in the ovaries post-blood meal. In vivo and ex vivo assays using exogenous insulins and Rhopr-AKH, reveal that Rhopr-TRET is up-regulated in ovaries by both peptide families. In accordance with these results, when ILP and AKH signaling cascades are impaired using RNA interference, Rhopr-TRET transcript is down-regulated. In addition, trehalose injection induces an up-regulation of Rhopr-TRET transcript expression and suggests an activation of insulin signaling. Overall, the results support the hypothesis of a direct trehalose uptake by ovaries from the hemolymph through Rhopr-TRET, regulated by ILP and/or AKH. We also show that Rhopr-TRET may work cooperatively with AKH signaling to support the release of trehalose from the ovaries into the hemolymph during the unfed (starved) condition. In conclusion, the results indicate that in females of R. prolixus, trehalose metabolism and its hormonal regulation by ILP and AKH play critical roles in adapting to different nutritional conditions and physiological states.

The Modulation of Trehalose Metabolism by 20-Hydroxyecdysone in Antheraea pernyi (Lepidoptera: Saturniidae) During its Diapause Termination and Post-Termination Period

Trehalose plays a crucial role in the diapause process of many insects, serving as an energy source and a stress protectant. Trehalose accumulation has been reported in diapause pupae of Antheraea pernyi; however, trehalose metabolic regulatory mechanisms associated with diapause termination remain unclear. Here, we showed that the enhanced trehalose catabolism was associated with an increase in endogenous 20-hydroxyecdysone (20E) in hemolymph of A. pernyi pupae during their diapause termination and posttermination period. Injection of 20E increased the mRNA level of trehalase 1A (ApTre-1A) and trehalase 2 (ApTre-2) of A. pernyi diapause pupae in a dose-dependent manner but did not affect the mRNA level of trehalase 1B (ApTre-1B). Meanwhile, exogenous 20E increased the enzyme activities of soluble and membrane-bound trehalase, leading to a decline in hemolymph trehalose. Conversely, the expression of ApTre-1A and ApTre-2 were down-regulated after the ecdysone receptor gene (ApEcRB1) was silenced by RNA interference or by injection of an ecdysone receptor antagonist cucurbitacin B (CucB), which inhibits the 20E pathway. Moreover, CucB treatment delayed adult emergence, which suggests that ApEcRB1 might be involved in regulating pupal-adult development of A. pernyi by mediating ApTre-1A and ApTre-2 expressions. This study provides an overview of the changes in the expression and activity of different trehalase enzymes in A. pernyi in response to 20E, confirming the important role of 20E in controlling trehalose catabolism during A. pernyi diapause termination and posttermination period.

Diapause hormone directly stimulates the prothoracic glands of diapause larvae under juvenile hormone regulation in the bamboo borer, Omphisa fuscidentalis Hampson

Larval diapause in many lepidopteran insects is induced and maintained by high juvenile hormone (JH). In the case of the bamboo borer, Omphisa fuscidentalis, the effect of JH is the opposite: The application of juvenile hormone analog (JHA: S-methoprene) terminates larval diapause, unlike in other insect species. Here, we analyzed the expression of JH-receptor Met, DH-PBAN, and Kr-h1 in the subesophageal ganglion (SG) from October to April using semi-quantitative polymerase chain reaction (PCR). The results show that OfMet and OfDH-PBAN messenger RNA in the SG are mainly expressed during the larval diapause stage, while OfKr-h1 increases during the pupal stage. Using tissue culture techniques and an enzyme-linked immunosorbent assay (ELISA), diapause hormone (DH) was found to induce ecdysteroidogenesis in the culture medium of the prothoracic gland (PG) after incubation for 30 min with 25 ng and 50 ng of DH. Thus, DH is a novel stimulator for the PG. We identified a DHR homolog in the bamboo borer and confirmed that it is expressed in the PG. In addition, for in vitro experiments, DH increased the expression levels of OfDHR, OfEcR-A, and ecdysone-inducible genes in the PG. These results demonstrate that DH can function as a prothoracicotropic factor, and this function of DH might be through of DHR expressed on PG cells. Consequently, DH is one of the key factors in larval diapause break which is triggered by JH in the bamboo borer, O. fuscidentalis.

Larval diapause termination in the bamboo borer, Omphisa fuscidentalis

In insects, juvenile hormone (JH) and 20-hydroxyecdysone (20E) regulate larval growth and molting. However, little is known about how this cooperative control is terminating larval diapause especially in the bamboo borer, Omphisa fuscidentalis. In both in vivo and in vitro experiments, we here measured the expression levels of genes which were affected by juvenile hormone analogue (JHA: S-methoprene) and 20-hydroxyecdysone (20E) in diapausing O. fuscidentalis larvae. Corresponding mRNA expression changes in the subesophageal ganglion (SG) and prothoracic gland (PG) were evaluated using qRT-PCR. The data showed similar response patterns of JH receptor gene (OfMet), diapause hormone gene (OfDH-PBAN), ecdysone receptor genes (OfEcR-A and OfEcR-B1) and ecdysone inducible genes (OfBr-C, OfE75A, OfE75B, OfE75C and OfHR3). JHA induced the expressions of OfMet and OfDH-PBAN in both SG and PG, whereas ecdysone receptor genes and ecdysone inducible genes were induced by JHA only in PG. For 20E treatment group, expressions of ecdysone receptor genes and ecdysone inducible genes in both SG and PG were increased by 20E injection. In addition, the in vitro experiments showed that OfMet and OfDH-PBAN were up-regulated by JHA alone, but ecdysone receptor genes and ecdysone inducible genes were up-regulated by JHA and 20E. However, OfMet and OfDH-PBAN in the SG was expressed faster than OfMet and OfDH-PBAN in the PG and the expression of ecdysone receptor genes and ecdysone inducible genes induced by JHA was much later than observed for 20E. These results indicate that JHA might stimulate the PG indirectly via factors (OfMet and OfDH-PBAN) in the SG, which might be a regulatory mechanism for larval diapause termination in O. fuscidentalis.

Myosuppressin is involved in the regulation of pupal diapause in the cabbage army moth Mamestra brassicae

Diapause, a programmed developmental arrest, is common in insects, enabling them to survive adverse seasons. It is well established that pupal diapause is regulated by ecdysteroids secreted by the prothoracic glands (PGs), with cessation of ecdysteroid secretion after pupal ecdysis leading to pupal diapause. A major factor regulating the gland activity is prothoracicotropic hormone (PTTH) secreted from the brain. In our previous study, we demonstrated that the cessation of PTTH release after pupal ecdysis resulted in the inactivation of the PGs, leading to pupal diapause in the cabbage army moth Mamestra brassicae. Here we show that a neuropeptide myosuppressin also contributes to the inactivation of PGs at the initiation of diapause. Myosuppressin suppresses PTTH-stimulated activation of the PGs in vitro. Concentrations of myosuppressin in the hemolymph after pupal ecdysis are higher in diapause pupae than in nondiapause pupae.

Effects of juvenile hormone (JH) analog insecticides on larval development and JH esterase activity in two spodopterans

Juvenile hormone analog (JHA) insecticides are biological and structural mimics of JH, a key insect developmental hormone. Toxic and anti-developmental effects of the JHA insecticides methoprene, fenoxycarb, and pyriproxyfen were investigated on the larval and pupal stages of Spodoptera littoralis and Spodoptera frugiperda. Bioassays showed that fenoxycarb has the highest toxicity and fastest speed of kill in 2nd instar S. littoralis. All three JHAs affected the development of 6th instar (i.e., final instar) and pupal S. frugiperda. JH esterase (JHE) is a critical enzyme that helps to regulate JH levels during insect development. JHE activity in the last instar S. littoralis and S. frugiperda was 11 and 23 nmol min(-1) ml(-1) hemolymph, respectively. Methoprene and pyriproxyfen showed poor inhibition of JHE activity from these insects, whereas fenoxycarb showed stronger inhibition. The inhibitory activity of fenoxycarb, however, was more than 1000-fold lower than that of OTFP, a highly potent inhibitor of JHEs. Surprisingly, topical application of methoprene, fenoxycarb or pyriproxyfen on 6th instars of S. littoralis and S. frugiperda prevented the dramatic reduction in JHE activity that was found in control insects. Our findings suggest that JHAs may function as JH agonists that play a disruptive role or a hormonal replacement role in S. littoralis and S. frugiperda.

Biosynthesis, Turnover, and Functions of Chitin in Insects

Chitin is a major component of the exoskeleton and the peritrophic matrix of insects. It forms complex structures in association with different assortments of cuticle and peritrophic matrix proteins to yield biocomposites with a wide range of physicochemical and mechanical properties. The growth and development of insects are intimately coupled with the biosynthesis, turnover, and modification of chitin. The genes encoding numerous enzymes of chitin metabolism and proteins that associate with and organize chitin have been uncovered by bioinformatics analyses. Many of these proteins are encoded by sets of large gene families. There is specialization among members within each family, which function in particular tissues or developmental stages. Chitin-containing matrices are dynamically modified at every developmental stage and are under developmental and/or physiological control. A thorough understanding of the diverse processes associated with the assembly and turnover of these chitinous matrices offers many strategies to achieve selective pest control.

Sublethal effects of the chitin synthesis inhibitor, hexaflumuron, in the cotton mirid bug, Apolygus lucorum (Meyer-Dür)

Hexaflumuron is a type of benzoylphenylurea insecticide which is highly toxic for many insects. Sublethal doses of hexaflumuron have been shown to significantly affect insect growth and development. However, the action mechanism of hexaflumuron is not well understood. In the present study, first instar Apolygus lucorum nymphs were exposed to sublethal doses of hexaflumuron based on the estimated 120h acute LC50 valve of 20.53mg/ml. We found that exposure to sublethal hexaflumuron doses resulted in a significant increase in development time and reduced the weights of fifth instar A. lucorum nymphs. We also measured trehalose, which is a primary blood sugar in insects, and the enzyme trehalase that is involved in energy metabolism. Trehalose content in first instar nymphs significantly increased following hexaflumuron treatment while the glucose content, soluble trehalase activity and expression levels of ALTre-1 mRNA decreased significantly. However, no significant changes in membrane-bound trehalase activity and ALTre-2 mRNA expression were observed. In addition, these decreases or increases could be correlated to increases in treatment time or concentration of hexaflumuron, respectively. The present findings indicated that sublethal doses of hexaflumuron could interfere the normal carbohydrate metabolism by depressing the expression of ALTre-1 in A. lucorum, which provide valuable information on the physiology and molecular mechanisms for the toxicity of hexaflumuron.

Molecular characterization and gene expression of juvenile hormone binding protein in the bamboo borer, Omphisa fuscidentalis

Juvenile hormone (JH) plays an important role in many physiological processes in insect development, diapause and reproduction. An appropriate JH titer in hemolymph is essential for normal development in insects. Information concerning its carrier partner protein, juvenile hormone binding protein (JHBP), provides an alternative approach to understanding how JH regulates metamorphosis. In this study, we cloned and sequenced the Omphisa juvenile hormone binding protein (OfJHBP). The full-length OfJHBP cDNA sequence is comprised of 849 nucleotides with an open reading frame of 726bp encoding 242 amino acids. The molecular mass of the protein was estimated to be 26.94kDa. The deduced protein sequence of OfJHBP showed moderate homology with the lepidopteran, Heliothis virescens JHBP (52% amino acid identity) and lower homology with the Bombyx mori JHBP (45%) and the Manduca sexta JHBP (44%). The OfJHBP was expressed mainly in the fat body. OfJHBP transcripts in the fat body was moderately high during 3rd, 4th and 5th instars, then rapidly increased, reaching a peak during early diapause. The expression remained high in mid-diapause, then decreased in late-diapause until the pupal stage. Both juvenile hormone analog (JHA), methoprene, 20-hydroxyecdysone (20E) exhibited a similar stimulatory pattern in OfJHBP expression of diapausing larvae. OfJHBP mRNA levels gradually increased and showed a peak of gene expression on the penultimate, then declined to low levels in the pupal stage. For in vitro gene expression, both of JHA and 20E induced OfJHBP mRNA expression in fat body. Fat body maintenance in vitro in the presence of 0.1μg/50μl JHA induced OfJHBP mRNA expression to high levels within the first 30min whereas 0.1μg/50μl 20E induced gene expression at 120min. To study the synergistic effect of these two hormones, fat body was incubated in vitro with 0.1μg/50μl JHA or 0.1μg/50μl 20E or a combination of both hormone for 30min. Induction of OfJHBP expression by JHA and 20E was significantly greater than that of either hormone alone. These results should contribute to our understanding of how JHBP and JH regulate the termination of larval diapause in the bamboo borer.

Programmed cell death of larval tissues induced by juvenile hormone in the bamboo borer, Omphisa fuscidentalis

Programmed cell death (PCD) plays a critical role during animal development through the destruction of unneeded cells and tissues. In some insects, the prothoracic glands (PGs) and anterior silk glands (ASGs) are larval-specific tissues that are normally eliminated by PCD after pupation. Previous studies report that juvenile hormone analog (JHA) terminates the larval diapause of Omphisa fuscidentalis by increasing the hemolymph ecdysteroids that trigger PCD. Because JHA may indirectly induce the PCD of the PGs and ASGs of Omphisa diapausing larvae, the effects of JHA on the induction of PCD were determined. The application of 1μg JHA induced PCD in the PGs and ASGs of larvae identified as stage G0 (prior to pupation). The injection of 1μg 20E triggered the PCD of the ASGs when the larvae expressed a G0-G1 morphology, whereas PCD occurred in the PGs on day 1 post-injection. Histological studies revealed similar patterns of morphological changes during the PG and ASG PCD in the JHA- and 20E-treated larvae. Furthermore, to confirm that PCD was induced by a high ecdysteroid level that increases after JHA application, the expression profiles of EcR-A and EcR-B1 in the PGs and ASGs from the JHA-treated larvae were examined, and the results showed that the expression levels of EcR-A and EcR-B1 mRNA increased during the G0 stage. These results suggest that JHA may be involved in PCD by increasing the ecdysteroid titer, leading to termination of the larval diapause period in Omphisa fuscidentalis.

The effects of triazophos on the trehalose content, trehalase activity and their gene expression in the brown planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

A previous study demonstrated that the flight capacity of Nilaparvata lugens adults treated with triazophos was enhanced significantly. However, the physiological and regulative mechanisms of the flight enhancement are not well understood. Trehalose is a primary blood sugar in insects, and the enzyme trehalase is involved in energy metabolism. The present study investigated the effects of triazophos on the trehalose content, trehalase activity (soluble trehalase and membrane-bound trehalase) and the mRNA transcript levels of their corresponding genes (NlTre-1 and NlTre-2) in fifth instar nymphs, as well as in the brachypterous and macropterous N. lugens adult females. Our findings showed that the trehalose content in fifth instar nymphs as well as in the brachypterous and the macropterous adults significantly decreased following triazophos treatment. However, the glucose content, soluble trehalase activity and expression level of NlTre-1 mRNA increased significantly compared to the controls. No significant enhancement of NlTre-2 expression was found, indicating that regulation of energy metabolism of triazophos-induced flight capacity in N. lugens was not associated with NlTre-2 expression. In addition, soluble trehalase activity and the expression level of NlTre-1 mRNA in the macropterous females was significantly higher than that in the brachypterous females. The present findings provide valuable information on the molecular and regulative mechanisms of the increased flight capacity found in adult N. lugens after treatment with triazophos.

Identification of 20-hydroxyecdysone late-response genes in the chitin biosynthesis pathway

Background

20-hydroxyecdysone (20E) and its receptor complex ecdysone receptor (EcR) and ultraspiracle (USP) play a crucial role in controlling development, metamorphosis, reproduction and diapause. The ligand-receptor complex 20E-EcR/USP directly activates a small set of early-response genes and a much larger set of late-response genes. However, ecdysone-responsive genes have not been previously characterized in the context of insect chitin biosynthesis.

Principal Findings

Here, we show that injection-based RNA interference (RNAi) directed towards a common region of the two isoforms of SeEcR in a lepidopteron insect Spodoptera exigua was effective, with phenotypes including a high mortality prior to pupation and developmental defects. After gene specific RNAi, chitin contents in the cuticle of an abnormal larva significantly decreased. The expression levels of five genes in the chitin biosynthesis pathway, SeTre-1, SeG6PI, SeUAP, SeCHSA and SeCHSB, were significantly reduced, while there was no difference in the expression of SeTre-2 prior to 72 hr after injection of EcR dsRNA. Meanwhile, injection of 20E in vivo induced the expression of the five genes mentioned above. Moreover, the SeTre-1, SeG6PI, SeUAP and SeCHSB genes showed late responses to the hormone and the induction of SeTre-1, SeG6PI, SeUAP and SeCHSB genes by 20E were able to be inhibited by the protein synthesis inhibitor cycloheximide in vitro indicating these genes are 20E late-response genes.

Conclusions

We conclude that SeTre-1, SeG6PI, SeUAP and SeCHSB in the chitin biosynthesis pathway are 20E late-response genes and 20E and its specific receptors plays a key role in the regulation of chitin biosynthesis via inducing their expression.

Characterization of putative soluble and membrane-bound trehalases in a hemipteran insect, Nilaparvata lugens

Trehalose is the main blood sugar of insects, and the enzyme trehalase is involved in energy metabolism and controlling trehalose levels in cells. Two forms (soluble and membrane-bound) of trehalase and the corresponding genes (NlTre-1 and NlTre-2) were identified from the brown planthopper, Nilaparvata lugens. Both NlTre-1 and NlTre-2 contain trehalase signature motifs, and NlTre-2 contains a putative transmembrane domain. Comparison of trehalase activity and gene mRNA level at different developmental stages, or following application of 20-hydroxyecdysone (20E), suggests that NlTre-1 and NlTre-2 encode a soluble trehalase and a membrane-bound trehalase respectively. Soluble trehalase activity accounted for the majority of total trehalase activity in N. lugens. Only soluble trehalase activity and NlTre-1 mRNA level could be induced by 20E. Additionally, only soluble trehalase activity was significantly higher in macropterous individuals than in brachypterous morphs. These results indicate that only soluble trehalase is differentially expressed between macropterous and brachypterous individuals and is more responsive to hormone stimulus.

Synthesis and mobilization of glycogen and trehalose in adult male Rhodnius prolixus

The vector of Chagas' disease, Rhodnius prolixus, feeds exclusively on blood. The blood meals are slowly digested, and these insects wait some weeks before the next meal. During the life of an insect, energy-requiring processes such as moulting, adult gonadal and reproductive growth, vitellogenesis, muscular activity, and fasting, lead to increased metabolism. Carbohydrates are a major source of energy and their mobilization is important. We determined the amounts of glycogen, trehalose, and glucose present in the fat body and/or hemolymph of adult males of R. prolixus and recorded the processes of accumulation and mobilization of these carbohydrates. We also tested our hypothesis that these processes are under endocrine control. The amount of glycogen in the fat body progressively increased until the fourth day after feeding (from 9.3+/-2.2 to 77. 3+/-7.5 microg/fat body), then declined to values around 36.3+/-4.9 microg/fat body on the fifteenth day after the blood meal. Glycogen synthesis was eliminated in decapitated insects and head-transplanted insects synthesized glycogen. The amount of trehalose in the fat body increased until the sixth day after feeding (from 16. 6+/-1.7 to 40. 6+/-5.3 nmol/fat body), decreased abruptly, and stabilized between days 7 and 15 at values ranging around 15-19 nmol/fat body. Decapitated insects did not synthesize trehalose after feeding, and this effect was reversed in head-transplanted insects. The concentration of trehalose in the hemolymph increased after the blood meal until the third day (from 0.07+/-0.01 to 0.75+/-0.05 mM) and at the fourth day it decreased until the ninth day (0.21+/-0.01 mM), when it increased again until the fourteenth day (0.79+/-0.06 mM) after the blood meal, and then declined again. In decapitated insects, trehalose concentrations did not increase soon after the blood meal and at the third day it was very low, but on the fourteenth day it was close to the control values. The concentration of glucose in the hemolymph of untreated insects remained low and constant (0.18+/-0.01 mM) during the 15 days after feeding, but in decapitated insects it progressively increased until the fifteenth day (2.00+/-0.10 mM). We recorded the highest trehalase activity in midgut, which was maximal at the eighth day after feeding (2,830+/-320 nmol of glucose/organ/h). We infer that in Rhodnius prolixus, the metabolism of glycogen, glucose, and trehalose are controlled by factors from the brain, according to physiological demands at different days after the blood meal.

Deciphering proteomic signatures of early diapause in Nasonia

Insect diapause is an alternative life-history strategy used to increase longevity and survival in harsh environmental conditions. Even though some aspects of diapause are well investigated, broader scale studies that elucidate the global metabolic adjustments required for this remarkable trait, are rare. In order to better understand the metabolic changes during early insect diapause, we used a shotgun proteomics approach on early diapausing and non-diapausing larvae of the recently sequenced hymenopteran model organism Nasonia vitripennis. Our results deliver insights into the molecular underpinnings of diapause in Nasonia and corroborate previously reported diapause-associated features for invertebrates, such as a diapause-dependent abundance change for heat shock and storage proteins. Furthermore, we observed a diapause-dependent switch in enzymes involved in glycerol synthesis and a vastly changed capacity for protein synthesis and degradation. The abundance of structural proteins and proteins involved in protein synthesis decreased with increasing diapause duration, while the abundance of proteins likely involved in diapause maintenance (e.g. ferritins) increased. Only few potentially diapause-specific proteins were identified suggesting that diapause in Nasonia relies to a large extent on a modulation of pre-existing pathways. Studying a diapause syndrome on a proteomic level rather than isolated pathways or physiological networks, has proven to be an efficient and successful avenue to understand molecular mechanisms involved in diapause.

Regulation of soluble and membrane-bound trehalase activity and expression of the enzyme in the larval midgut of the bamboo borer Omphisa fuscidentalis

Diapausing larvae of Omphisa fuscidentalis contain soluble and membrane-bound trehalase in the midgut. Soluble trehalase activity accounts for three-fourths of the total trehalase activity in midgut homogenates. The exposure of diapausing larvae to juvenile hormone analog (JHA) induced pupation, accompanied by an increase in soluble trehalase activity at the beginning of the prepupal period. Injection of 20-hydroxyecdysone (20E) increased the level of soluble trehalase activity 5 days postinjection in a dose-dependent manner. In contrast, no increase in membrane-bound trehalase activity was observed under the same conditions. We cloned the cDNAs that encode the soluble and membrane-bound forms of trehalase in O. fuscidentalis trehalase-1 (OfTreh-1) and trehalase-2 (OfTreh-2), respectively. Treh-1 encodes a 581-aa protein while Treh-2 encodes a 648-aa protein with one putative transmembrane domain near the C-terminus. The mRNA expression level of Treh-1 was 27-fold higher than that of Treh-2 in diapausing larval midgut. Following the exposure of diapausing larvae to JHA, Treh-1 mRNA expression increased gradually until the prepupal period whereupon it increased dramatically; in contrast, the mRNA expression of Treh-2 remained at its initial level. Similarly, 20E upregulated Treh-1 expression but had no effect on Treh-2 expression. Taken together, these results suggest that an increase in the soluble trehalase activity at pupation is caused by upregulation of Treh-1 gene. Moreover, membrane-bound trehalase does not appear to be involved in the dynamic changes in the hemolymph trehalose concentration that occur during the larval-pupal transformation.

Dual control of midgut trehalase activity by 20-hydroxyecdysone and an inhibitory factor in the bamboo borer Omphisa fuscidentalis Hampson

During larval diapause lasting 9 months from September to May, trehalase activity in the midgut of the bamboo borer Omphisa fuscidentalis Hampson (Lepidoptera: Crambidae) was low from December to April, followed by a fourfold increase in May that remained high during the pupal stage in July. An application of juvenile hormone analog (JHA) produced increases in the ecdysteroid titer, while trehalase activity was increased by both JHA and 20-hydroxyecdysone (20E) injection. The trehalase activity in the midgut of diapausing larvae was doubled by incubating the midgut with 20E for 48h. During diapause as well as after JHA application, expression of two ecdysone receptor isoform genes (EcR-A and EcR-B1) in the midgut increased simultaneously with the increase in hemolymph ecdysteroid titer, followed by an increase in trehalase activity. The hemolymph of diapausing larvae contained a trehalase inhibitor and inhibitory activity was high during diapause. After 20E injection, trehalase inhibition decreased as midgut trehalase activity increased. Taken together, at least two factors may participate in the change in midgut trehalase activity: increase in trehalase activity and decrease in trehalase inhibitor activity, both of which may be induced by 20E.

Identification, characterization, and developmental regulation of two storage proteins in the bamboo borer Omphisa fuscidentalis

Two insect storage proteins, OfSP1 (75 kDa) and OfSP2 (72 kDa), were purified using three different chromatographies from the hemolymph of Omphisa fuscidentalis larvae during diapause, and their genes were cloned. OfSP1 and OfSP2 concentrations in the hemolymph were high during diapause. During pupation, OfSP1 levels decreased in the male hemolymph and disappeared from the female hemolymph. OfSP1 and OfSP2 mRNA levels in the fat bodies were low during the third instar, but increased greatly during the fourth and fifth larval instars. During diapause, mRNA expression continued at a lower level than during the feeding period. The injection of 20-hydroxyecdysone (20E) into diapausing larvae caused an increase in OfSP1 and OfSP2 mRNA levels 2-3 days post-injection, followed by a decrease in expression until pupation, which occurred 2-4 days thereafter. When larvae were treated with juvenile-hormone analog (JHA), OfSP1 and OfSP2 mRNA levels gradually decreased until the onset of pupation. In Omphisa, OfSP1 and OfSP2 proteins are produced and released by the larval fat bodies in the fourth and fifth-instar larvae, and the proteins accumulate in the hemolymph until the insects enter diapause. OfSP1 may be reabsorbed by the fat bodies at the end of diapause for subsequent re-use during pupation.

Correlation of oxygen consumption, cytochrome c oxidase, and cytochrome c oxidase subunit I gene expression in the termination of larval diapause in the bamboo borer, Omphisa fuscidentalis

The moth Omphisa fuscidentalis (Lepidoptera, Pyralidae) is a univoltine insect with a larval diapause period lasting up to 9 months. We studied changes in O(2) consumption in conjunction with cytochrome c oxidase activity and cytochrome c oxidase subunit I (cox1) gene expression. O(2) consumption changed within a day, showing a supradian rhythm with a ca.12-h cycle at 25 degrees C. During the first two-thirds of the diapause period, from October to March, O(2) consumption was constant until January and then increased by March. Topical application of methoprene, a juvenile hormone analog (JHA), to diapausing larvae terminated the diapause and was associated with an increase in O(2) consumption rate at diapause termination. In JHA-treated larvae, cytochrome c oxidase activity in fat bodies was high at the beginning of the prepupal period and highest at pupation. cox1 expression in fat bodies displayed a transient peak 8 days after JHA application and peaked in the prepupal period. Taken together, our results show that the break of diapause by JHA is associated with the activation of cox1, bringing about an increase in cytochrome c oxidase activity, followed by an increase in O(2) consumption rate.

Eco-physiological phases of insect diapause

Insect diapause is a dynamic process consisting of several successive phases. The conception and naming of the phases is unsettled and, sometimes, ambiguous in the literature. In this paper, the ontogeny of diapause was reviewed and the most often used terms and the best substantiated phases were highlighted, explained and re-defined. The aim was to propose relatively simple and generally applicable terminological system. The phases of diapause induction, preparation, initiation, maintenance, termination and post-diapause quiescence were distinguished. The specific progression through diapause phases in each species, population (genotype), or even individual, is based on (thus far largely unknown) physiological processes, the actual expression of which is significantly modified by diverse environmental factors. Thus, such phases are eco-physiological in their nature.

Germ cell death in the testis and its relation to spermatogenesis in the wax moth,Galleria mellonella (Lepidoptera: Pyralidae), effects of facultative diapause

The dichotomous spermatogenesis of many Lepidopterans results in the production of two types of sperm: eupyrene sperm possessing a cell nucleus which participates in fertilisation, and apyrene ones, which lose their nuclei during development and whose function remains a mystery. The goal of our study was to analyse spermatogenesis at the end of the larval development of the wax moth, Galleria mellonella, at an optimal temperature of 30 degrees C as well as to describe how they are affected by diapause brought on by a reduction of temperature to 18 degrees C. Spermatogenesis in non-diapausing insects did not differ significantly from that described in other species of Lepidoptera, and any differences found were compared against available literature. Based on the results presented, it may be unequivocally stated that changes in spermatogenesis occur in diapause caused by a suboptimal temperature of 18 degrees C. The main effect of diapause observed in the testes is the degeneration of germ cells, immediately following their differentiation from bipotential spermatocytes. Eupyrene cells seem to reach a more advanced stage of development. Due to the absence of secondary eupyrene spermatocytes in the testis of diapausing insects, it may be surmised that the meiotic divisions, which lead to the formation of secondary spermatocytes and eventually spermatids, do not occur, or are somehow altered. Lastly, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) analyses we performed show that the degenerative changes of eupyrene cells are apoptotic in character.

Evidence for the presence of a threshold weight for entering diapause in the yellow-spotted longicorn beetle, Psacothea hilaris

Under long-day conditions larvae of Psacothea hilaris (Coleoptera: Cerambycidae) pupate after the 4th or 5th instar, while under short-day conditions they undergo 2-4 nonstationary supernumerary molts and eventually enter diapause. To explore the possibility of a threshold weight for entering diapause, P. hilaris larvae were deprived of food on days 0 (day of ecdysis), 4 or 8 of the 4th, 5th and 6th instars under short-day conditions. Within the first 40 days of starvation, 60% of the larvae starved starting on day 0 of the 4th instar died, but all the larvae starved at later stages survived. The incidence of diapause in these survivors was determined by the occurrence of pupation after a temporary chilling at 15 degrees C for 15 days. Diapause incidence increased as the onset of starvation was delayed; from 11% in the larvae starved on day 0 of the 5th instar to 100% in the larvae starved on day 4 and day 8 of the 6th instar. Analysis of the relationship between the initial weight of a respective larva at the onset of starvation and its pupation success revealed that none of the larvae weighing <or=540 mg pupated but all the larvae weighing >690 mg did. This finding suggests the presence of a threshold weight (about 600 mg), below which larvae are incapable of entering diapause. We discuss these findings with reference to the life history of P. hilaris.