Juvenile Hormone Esterase Activity Research Articles

Investigating the Regulatory Mechanism of the Sesquiterpenol Nerolidol from a Plant on Juvenile Hormone-Related Genes in the Insect Spodoptera exigua.

Various plant species contain terpene secondary metabolites, which disrupt insect growth and development by affecting the activity of juvenile hormone-degrading enzymes, and the juvenile hormone (JH) titers maintained in insects. Nerolidol, a natural sesquiterpenol belonging to the terpenoid group, exhibits structural similarities to insect JHs. However, the impact of nerolidol on insect growth and development, as well as its underlying molecular mechanism, remains unclear. Here, the effects of nerolidol on Spodoptera exigua were investigated under treatment at various sub-lethal doses (4.0 mg/mL, 1.0 mg/mL, 0.25 mg/mL). We found that a higher dose (4.0 mg/mL) of nerolidol significantly impaired the normal growth, development, and population reproduction of S. exigua, although a relatively lower dose (0.25 mg/mL) of nerolidol had no significant effect on this growth and development. Combined transcriptome sequencing and gene family analysis further revealed that four juvenile hormone esterase (JHE)-family genes that are involved in juvenile hormone degradation were significantly altered in S. exigua larvae after nerolidol treatment (4.0 mg/mL). Interestingly, the juvenile hormone esterase-like (JHEL) gene Sexi006721, a critical element responsive to nerolidol stress, was closely linked with the significant augmentation of JHE activity and JH titer in S. exigua (R2 = 0.94, p < 0.01). Taken together, we speculate that nerolidol can function as an analog of JH by modulating the expression of the enzyme genes responsible for degrading JH, resulting in JH disorders and ultimately disrupting the development of insect larvae. This study ultimately provides a theoretical basis for the sustainable control of S. exigua in the field whilst proposing a new perspective for the development of novel biological pesticides.

Modulation of Juvenile Hormone Esterase Gene Expression Against Development of Plutella xylostella (Lepidoptera: Plutellidae).

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a widespread and destructive pest of cruciferous crops. Owing to its increasing resistance to conventional pesticides, new strategies need to be developed for diamondback moth control. Here, we investigated factors that modulate juvenile hormone esterase (JHE) activity and jhe (Px004817) transcription, and determined the effects of these factors on subsequent growth and development in diamondback moth. Starvation inhibited JHE activity and jhe transcription, increased mortality, and decreased the rate of molting from the third- to the fourth-instar stages. Larvae kept at 32°C molted earlier and showed increased JHE activity and jhe transcription after 24-h treatment. Exposure to 1,325 mg/liter OTFP (3-octylthio-1,1,1-trifluoro-2-propanone) delayed molting and pupation, increased pupal weight, and decreased JHE activity and jhe transcription at both 24 and 48 h. Treatment with 500 mg/liter pyriproxyfen delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. A combination of OTFP (1,325 mg/liter) and pyriproxyfen (500 mg/liter) induced the highest mortality, delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. These effects on JHE activity and jhe transcription were similar to those in insects treated only with pyriproxyfen. The results demonstrated that JHE and jhe (Px004817) were involved in the responses of diamondback moth to external modulators and caused changes in growth and development. The combination of OTFP and pyriproxyfen increased the effectiveness of action against diamondback moth.

Entomopoxvirus infection induces changes in both juvenile hormone and ecdysteroid levels in larval Mythimna separata.

Insect viruses are among the most important pathogens of lepidopteran insects. Virus-infected larvae often show developmental defects including a prolonged larval period and a failure to pupate, but the mechanisms by which insect viruses regulate host development need further investigation. In this study, the regulation of host endocrinology by a lepidopteran entomopoxvirus (EPV), Mythimna separata EPV (MySEV), was examined. When fourth instar M. separata were inoculated with MySEV occlusion bodies, pupation was prevented and the insects died during the final (sixth) larval instar. Liquid chromatography-MS analysis revealed that juvenile hormone (JH) titres in the haemolymph of MySEV-infected sixth instars were higher than those in mock-infected larvae. JH esterase (JHE) activity was also examined by kinetic assay using a colorimetric substrate. The level of JHE activity in the haemolymph of MySEV-infected larvae was generally lower than that found in mock-infected larvae. In contrast, ecdysteroid titre in the haemolymph of final-instar MySEV-infected larvae was lower than that found in mock-infected larvae when measured by radioimmunoassay. A statistically significant difference in the release of ecdysteroids from prothoracic glands (PGs) that were dissected from MySEV- or mock-infected sixth instar Day 3 larvae was not found following prothoracicotropic hormone (PTTH) exposure. Our results indicate that the release of ecdysteroids was reduced not by infection of the PGs by MySEV, but by reduced PTTH production from the brain. Taken together our study suggests that EPVs retard host development by both reducing ecdysone titre and maintaining status quo levels of JH by preventing its metabolism.

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 23nmolmin−1ml−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.

In Vitro and in Vivo Inhibition of Haemolymph Juvenile Hormone Esterase Activity by the Ethanol Extract of Clerodendrum inerme in Fifth Instar Larva of Castor Semilooper, Achaea janata (L.)

Juvenile hormone (JH) is a unique hormone in insects that controls growth, development, metamorphosis and reproduction. It has been well established that JH esterase is an enzyme involved in JH regulation. Results of both in vitro and in vivo studies revealed that ethanol leaf extract of Clerodendrum inerme significantly inhibits haemolymph JH esterase activity affecting growth and normal development of the test insect, castor semilooper ( Achaea janata ), a serious pest of oil seed crops like castor and groundnut.

Exposure of Daphnia magna to trichloroethylene (TCE) and vinyl chloride (VC): Evaluation of gene transcription, cellular activity, and life-history parameters

Trichloroethylene (TCE) is a ubiquitous contaminant classified as a human carcinogen. Vinyl chloride (VC) is primarily used to manufacture polyvinyl chloride and can also be a degradation product of TCE. Very few data exist on the toxicity of TCE and VC in aquatic organisms particularly at environmentally relevant concentrations. The aim of this study was to evaluate the sub-lethal effects (10day exposure; 0.1; 1; 10µg/L) of TCE and VC in Daphnia magna at the gene, cellular, and life-history levels. Results indicated impacts of VC on the regulation of genes related to glutathione-S-transferase (GST), juvenile hormone esterase (JHE), and the vitelline outer layer membrane protein (VMO1). On the cellular level, exposure to 0.1, 1, and 10µg/L of VC significantly increased the activity of JHE in D. magna and TCE increased the activity of chitinase (at 1 and 10µg/L). Results for life-history parameters indicated a possible tendency of TCE to affect the number of molts at the individual level in D. magna (p=0.051). Measurement of VG-like proteins using the alkali-labile phosphates (ALP) assay did not show differences between TCE treated organisms and controls. However, semi-quantitative measurement using gradient gel electrophoresis (213–218kDa) indicated significant decrease in VG-like protein levels following exposure to TCE at all three concentrations. Overall, results indicate effects of TCE and VC on genes and proteins related to metabolism, reproduction, and growth in D. magna.

Juvenile hormone (JH) esterase activity but not JH epoxide hydrolase activity is downregulated in larval Adoxophyes honmai following nucleopolyhedroviruses infection

Juvenile hormones (JHs) and ecdysteroids are critical insect developmental hormones. JH esterase (JHE) and JH epoxide hydrolase (JHEH) are JH-selective enzymes that metabolize JH and thus regulate the titer of JH. Baculoviruses are known to alter host endocrine regulation. The nucleopolyhedroviruses, AdhoNPV and AdorNPV, are known to have slow and fast killing activity against Adoxophyes honmai (Lepidoptera: Tortricidae), respectively. Here we found that when penultimate (4th) instar A. honmai are inoculated with AdhoNPV or AdorNPV, the mean survival time is 9.7 and 8.2days, respectively. The larvae molted once but did not pupate. The AdhoNPV- or AdorNPV-infected larvae did not show a dramatic increase in JHE activity as was found in mock-infected larvae, instead they showed a marked decrease in JHE activity. In contrast, both viral infections had no effect on JHEH activity. In order to further characterize the JHE activity, the JHE-coding sequence of A. honmai (ahjhe) was cloned and confirmed to encode a biologically active JHE. Quantitative real-time PCR analysis of ahjhe expression in 4th and 5th instar A. honmai revealed that AdhoNPV and AdorNPV are able to reduce ahjhe expression levels.

A whole genome screening and RNA interference identify a juvenile hormone esterase-like gene of the diamondback moth, Plutella xylostella

Juvenile hormone (JH) plays a crucial role in preventing precocious metamorphosis and stimulating reproduction. Thus, its hemolymph titer should be under a tight control. As a negative controller, juvenile hormone esterase (JHE) performs a rapid breakdown of residual JH in the hemolymph during last instar to induce a larval-to-pupal metamorphosis. A whole genome of the diamondback moth (DBM), Plutella xylostella, has been annotated and proposed 11 JHE candidates. Sequence analysis using conserved motifs commonly found in other JHEs proposed a putative JHE (Px004817). Px004817 (64.61kDa, pI=5.28) exhibited a characteristic JHE expression pattern by showing high peak at the early last instar, at which JHE enzyme activity was also at a maximal level. RNA interference of Px004817 reduced JHE activity and interrupted pupal development with a significant increase of larval period. This study identifies Px004817 as a JHE-like gene of P. xylostella.

Structure–activity relationship study of trifluoromethylketone inhibitors of insect juvenile hormone esterase: Comparison of several classification methods

Juvenile hormone esterase (JHE) plays a key role in the development and metamorphosis of holometabolous insects. Its inhibitors could possibly be targeted for insect control. Conversely, JHE may also be involved in endocrine disruption by xenobiotics, resulting in detrimental effects in beneficial insects. There is therefore a need to know the structural characteristics of the molecules able to monitor JHE activity, and to develop SAR and QSAR studies to estimate their effectiveness. For a large diverse population of 181 trifluoromethylketones (TFKs) – the most potent JHE inhibitors known to date – we recently proposed a binary classification (active/inactive) using a support vector machine and Codessa structural descriptors. We have now examined, using the same data set and with the same descriptors, the applicability and performance of five other machine learning approaches. These have been shown able to handle high dimensional data (with descriptors possibly irrelevant or redundant) and to cope with complex mechanisms, but without delivering explicit directly exploitable models. Splitting the data into five batches (training set 80%, test set 20%) and carrying out leave-one-out cross-validation, led to good results of comparable performance, consistent with our previous support vector classifier (SVC) results. Accuracy was greater than 0.80 for all approaches. A reduced set of 15 descriptors common to all the investigated approaches showed good predictive ability (confirmed using a three-layer perceptron) and gives some clues regarding a mechanistic interpretation.

Teratocyte-secreting proteins of an endoparasitoid wasp, Cotesia plutellae, prevent host metamorphosis by altering endocrine signals

An endoparasitoid wasp, Cotesia plutellae, parasitizes young larvae of the diamondback moth, Plutella xylostella, with its parasitic factors of polydnavirus, venom, ovarian proteins, and teratocytes (TCs). TCs are originated from embryonic serosal membrane at hatch of C. plutellae egg. Injection of in vitro cultured TCs significantly prolonged a larval period of nonparasitized P. xylostella and impaired a larva-to-pupa metamorphosis. This developmental alteration was also induced by injection of TC-cultured medium (TCM). However, heat-treated TCM significantly lost the inhibitory activity against larval development of P. xylostella. Larvae treated with TC or TCM appeared to undergo abnormal endocrine conditions. Juvenile hormone esterase activity was significantly suppressed at early last instar by injection of TC or TCM. In addition, expression of ecdysone receptor at final instar was lost, but that of insulin receptor was maintained until the end of the larval period in TC or TCM treatment. A proteomic analysis of TCM predicted several teratocyte-secreting proteins (TSPs). The inhibitory effect of host development by TCs was significantly enhanced by an addition of another parasitic factor, C. plutellae bracovirus. These results suggest that C. plutellae TC plays a crucial role in alteration of host development by secreting TSPs.

Reduced activity of juvenile hormone esterase in microsporidia-infected Lymantria dispar larvae

Infection of the fat body of Lymantria dispar (Lep.: Lymantriinae) larvae with the microsporidium Vairimorpha disparis has severe effects on juvenile hormone (JH) metabolism of the host. Beginning 8days postinfection, activity of the JH degrading enzyme JH-esterase was significantly lower in the hemolymph of infected than uninfected larvae. Activity remained low as microsporidiosis progressed. JH titers were slightly elevated in infected larvae; the difference was not significant in most cases. This disturbance of JH metabolism may be due to generally impaired fat body functions and high demand for resources by the developing pathogen.

Improved insecticidal efficacy of a recombinant baculovirus expressing mutated JH esterase from Manduca sexta

Juvenile hormone esterase (JHE), a member of the carboxylesterase family (EC 3.1.1.1), metabolizes JH that is found in juvenile insects. A highly conserved amphipathic alpha helix is found on the surface of known JHEs. This helix is implicated in receptor-mediated binding and endocytosis of JHE by the pericardial cells resulting in the clearance of JHE activity from the hemolymph. In this study, Lys-204 and Arg-208 of the amphipathic alpha helix of the JHE of Manduca sexta (MsJHE) were mutated to histidine residues generating MsJHE-HH. Pharmacokinetic studies following the injection of MsJHE-HH into the hemocoel of larval M. sexta, Heliothis virescens, and Agrotis ipsilon indicated that MsJHE-HH and wild type MsJHE are cleared at similar rates. The infectivity (lethal concentration and lethal time) of a recombinant baculovirus, AcMsJHE-HH, expressing MsJHE-HH was not significantly different than that of a recombinant baculovirus, AcMsJHE, expressing MsJHE in first instars of H. virescens and A. ipsilon. However, the mass of AcMsJHE-HH-infected larvae was 40–50% lower than that of larvae infected with AcMsJHE, and 70–90% lower than that of wild type AcMNPV-infected larvae.

Sub-Lethal Effects of Fenvalerate on the Development, Fecundity, and Juvenile Hormone Esterase Activity of Diamondback Moth, Plutella xylostella (L.)

The toxicities of fenvalerate (20% EC) to the 3rd instar larvae of diamondback moth (DBM), Plutella xylostella (L.), reared on three host plants viz., radish, oilseed rape, and cabbage were tested. The LC 50 values of fenvalerate to the 3rd instar larvae of DBM varied with host plants, however, there wasn't any significant difference among them ( P > 0.05). Similarly, DBM fed on three host plants had same pupal weight, pupal period, pupation rate, adult emergence rate, female ratio, and fecundity. The activity of juvenile hormone esterase (JHE, EC 3.1.1.1) in the 3rd instar larvae of DMB did not significantly vary with host plants, either. These suggested that DBM had similar fitness on the three host plant species. When fed on the host plants pretreated with fenvalerate at the concentrations equivalent to LC 20, LC 50 and LC 80, the pupation rate, pupal weight, adult emergence rate, female ratio, fecundity, and JHE activity of the tested insects were declined as compared with insects in control treatments fed on the same host plant species. Furthermore, the pupal period of the tested insects was extended after fenvalerate treatment. The decrease in JHE activity after fenvalerate treatment in the tested insects could partly explain the changes in the mentioned growth parameters. Whether the role of fenvalerate in the inhibition of JHE activity could serve as a new way to control DBM needs further investigation.

A Novel Peptide Mediates Aggregation and Migration of Hemocytes from an Insect

Insect blood cells (hemocytes) comprise an essential arm of the immune system [1-7]. Several factors mediating recognition and phagocytosis of foreign intruders by hemocytes have been identified, but the mechanisms regulating hemocyte movement remain fragmentary. Embryonic hemocytes from Drosophila migrate along stereotypical routes in response to chemotactic signals from PVF ligands, members of the platelet-derived growth factor family [8-12]. Embryonic and larval hemocytes also accumulate at external wounds [11-13], but PVFs are not required for this response, suggesting involvement by other, unknown factors. Here we report the identification of hemocyte chemotactic peptide (HCP) from the moth Pseudaletia separata and present evidence that it stimulates aggregation and directed movement of phagocytic hemocytes. Spatiotemporal studies revealed that HCP is expressed in both epidermal cells and hemocytes, whereas structure-function studies identified post-translational modifications important for activity. HCP also shares similarities with another group of cytokines from moths called ENF peptides [14-17]. Taken together, our results identify HCP as a chemotactic cytokine that enhances clotting at wound sites in larvae.

Venom of Pteromalus puparum (Hymenoptera: Pteromalidae) induced endocrine changes in the hemolymph of its host, Pieris rapae (Lepidoptera: Pieridae)

Pteromalus puparum is a predominant endoparasitoid wasp of Pieris rapae. Its venom is the only active factor injected into host associated with oviposition. In this report, we explored whether the venom alone from this wasp affects the endocrine system of its host or not. We monitored the changes of hemolymph juvenile hormone (JH; only JH III detected), ecdysteroid, and juvenile hormone esterase activity (JHE) over 72 h in parasitized and venom-microinjected P. rapae pupae. Non-parasitized and PBS-microinjected P. rapae served as controls. Results showed that JH titers were significantly higher in parasitized and venom-microinjected pupae than that in control pupae during 24 to 72 h. After 12 h, JH titers were significantly promoted by parasitization and venom microinjection. JHE activities of non-parasitized and PBS-microinjected pupae were significantly higher than that of parasitized and venom-microinjected pupae, which was with a peak at 12 h (parasitized pupae) or 24 h (venom-microinjected pupae) during 6 to 48 and 12 to 36 h, respectively. The hemolymph titers of ecdysteroid in non-parasitized and PBS-microinjected pupae increased rapidly during 12 to 36 h with a peak at 36 h, and were higher than treatments before 48 h, while presenting a significant difference at 24 to 48 h between the treatments and controls. The results demonstrate that venom alone of this parasitoid wasp can disrupt its host's endocrine system.

Molecular cloning and characterization of a juvenile hormone esterase gene from brown planthopper, Nilaparvata lugens

Juvenile hormone (JH) plays key roles in the regulation of growth, development, diapause and reproduction in insects, and juvenile hormone esterase (JHE) plays an important role in regulating JH titers. We obtained a full-length cDNA encoding JHE in Nilaparvata lugens (NlJHE), the first JHE gene cloned from the hemipteran insects. The deduced protein sequence of Nljhe contains the five conserved motifs identified in JHEs of other insect species, including a consensus GQSAG motif that is required for the enzymatic activity of JHE proteins. Nljhe showed high amino acid similarities with Athalia rosae JHE (40%) and Apis mellifera JHE (39%). Recombinant NlJHE protein expressed in the baculovirus expression system hydrolyzed [ 3H] JH III at high activity and yielded the specificity constants ( k cat/ K M = 4.28 × 10 6 M −1 s −1) close to those of the validated JHEs from other insect species, indicating that Nljhe cDNA encodes a functional JH esterase. The Nljhe transcript was expressed mainly in the fat body and the expression level reached a peak at 48 h after ecdysis of the 5th instar nymphs. In the 5th instar, macropterous insects showed significantly higher Nljhe mRNA levels and JHE activities, but much lower JH III levels, than those detected in the brachypterous insects soon after ecdysis and at 48 h after ecdysis. These data suggest that NlJHE might play important roles in regulation of JH levels and wing form differentiation.

Tissue and stage-specific juvenile hormone esterase (JHE) and epoxide hydrolase (JHEH) enzyme activities and Jhe transcript abundance in lines of the cricket Gryllus assimilis artificially selected for plasma JHE activity: Implications for JHE microevolution

Fat body and midgut juvenile hormone esterase (JHE) and juvenile hormone epoxide hydrolase (JHEH) specific activities, and plasma JHE activity, were measured throughout the last stadium in two pairs (blocks) of lines of the cricket Gryllus assimilis, each pair of which had been artificially selected for high- or low-plasma JHE activity. Highly significant differences were observed between high- and low-activity lines of each block on most days for fat body JHE, and on one day for midgut JHE activity. In each block, line differences in developmental profiles for fat body JHE activity paralleled line differences in plasma JHE activity during the early-mid stadium, but not during the latter part of the stadium. The developmental profile of midgut JHE activity differed from that of plasma and fat body JHE activity, exhibiting peaks during the early and latter parts of the stadium. Midgut and fat body JHEH activities exhibited a mid-stadium peak in all lines, but activities were very similar in all lines. Fat body JHE appears to be a more significant contributor to plasma JHE than is midgut JHE. During the middle of the last stadium (day 4), Jhe transcript abundance was significantly higher in fat body or midgut of high- vs. low-JHE-activity lines. Jhe transcript abundance was positively correlated with JHE enzyme activity in either fat body or midgut, and with plasma JHE activity. Natural populations of G. assimilis harbor genetic variation for Jhe gene expression which appears to contribute to genetic variation in JHE specific activity in fat body and midgut. These genes appear to have been the targets of artificial selection that resulted in lines that differ dramatically in high- or low-plasma JHE activity. These genes appear to have little, if any, pleiotropic effects on JHEH specific activity.

Juvenile hormone esterase activity in the pupating and diapausing larvae of Sesamia nonagrioides

The development of the Mediterranean corn borer, Sesamia nonagrioides, under long-day (LD) photoperiod is associated with juvenile hormone (JH) decline and pupation in the 5th or 6th larval instar. The larvae grown under short-day (SD) conditions maintain a moderate JH titer and enter diapause during which they undergo several extra larval molts. Both types of larvae exhibit similar levels of juvenile hormone esterase (JHE) activity that increases in each instar during the period of low ecdysteroid titer and drops when the titer rises to a molt-inducing peak. A suppression of JHE activity within 24 h after application of an ecdysteroid agonist suggests that the drop of activity is a rapid and possibly direct response to ecdysteroids or their agonist. Esterase inhibitor 3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) suppressed more than 98% of the JHE activity without affecting pupation timing and adult development. The data indicate that JHE is not crucial for the switch between larval development, diapause, and metamorphosis in S. nonagrioides.

Synthesis and biological activity of novel anti-juvenile hormone agents

Ethyl 4-[2-(tert-butylcarbonyloxy)butoxy]benzoate (ETB) is a partial juvenile hormone (JH) antagonist which targets larval epidermis. We converted ETB to ethyl 4-(2-substituted alkyloxy)benzoates. These compounds induced precocious metamorphosis in the silkworm, Bombyx mori, which is a clear sign of JH deficiency, and their activity was completely counteracted by the simultaneous application of a JH agonist, methoprene. Among these novel compounds, ethyl 4-(2-benzylhexyloxy)benzoate (KF-13) showed high precocious metamorphosis-inducing activity at low doses, but its activity decreased with increasing dose, probably due to their JH-like activity. KF-13 is an enantiomeric compound. The (S)-enatiomer of KF-13 was more active than the (R)-enantiomer at low doses, but at high doses the activity was reversed (R>S). Hemolymph JH esterase activity, which is indispensable for the initiation of pupation in normal last-instar larvae, was induced in 4th-instar larvae by treatment with KF-13. 2-(6-Methyl-3-pyridyloxy)hexyl and 2-phenoxyhexyl analogs showed JH activity when topically applied to allatechtomized 4th-instar larvae.

Inhibition of juvenile hormone esterase activity in Lymantria dispar (Lepidoptera, Lymantriidae) larvae parasitized by Glyptapanteles liparidis (Hymenoptera, Braconidae)

Glyptapanteles liparidis is a gregarious, polydnavirus (PDV)-carrying braconid wasp that parasitizes larval stages of Lymantria dispar. In previous studies we showed that parasitized hosts dramatically increase juvenile hormone (JH) titers, whereas JH degradation is significantly inhibited in the hemolymph. Here we (i) quantified the effects of parasitism on JH esterase (JHE) activity in hemolymph and fat body of penultimate and final instars of L. dispar hosts and (ii) assessed the relative contribution of individual and combined wasp factors (PDV/venom, teratocytes, and wasp larvae) to the inhibition of host JHE activity. The effects of PDV/venom was investigated through the use of gamma-irradiated wasps, which lay non-viable eggs (leading to pseudoparasitization), while the effects of teratocytes and wasp larvae were examined by injection or insertion of these two components in either control or pseudoparasitized L. dispar larvae. Parasitism strongly suppressed host JHE activity in both hemolymph and fat body irrespective of whether the host was parasitized early (premolt-third instar) or late (mid-fourth instar). Down-regulation of JHE activity is primarily due to the injection of PDV/venom at the time of oviposition, with only very small additive effects of teratocytes and wasp larvae under certain experimental conditions. We compare the results with those reported earlier for L. dispar larvae parasitized by G. liparidis and discuss the possible role of JH alterations in host development disruption.