Influence of the braconid Glyptapanteles liparidis on the juvenile hormone titer of its larval host,the gypsy moth,Lymantria dispar

The increase in the juvenile hormone (JH) III titer in the hemolymph of Lymantria dispar larvae that were parasitized by the endoparasitoid braconid, Glyptapanteles liparidis, during the host's premolt to third instar, coincided with the molt of the parasitoid larvae to the second instar between day 5 and 7 of the fourth host instar. It reached a maximum mean value of 89 pmol/ml on day 7 of the fifth instar while it remained below 1 pmol/ml in unparasitized larvae. Only newly molted fifth instar hosts showed a low JH III titer similar to that of the unparasitized larvae. JH II, which is the predominant JH homologue in unparasitized gypsy moth larvae, also increased relative to controls in the last two samples (days 7 and 9) from parasitized fourth and fifth instars. Compared to unparasitized larvae, a generally reduced activity of JH esterase (JHE) was found in parasitized larvae throughout both larval stages. The reduction in enzyme activity at the beginning and at the end of each instar, when the JHE activity in unparasitized larvae was high, may be in part responsible for the increased JH II and JH III titers in parasitized larvae. Ester hydrolysis was the only pathway of JH metabolism in the hemolymph of unparasitized and parasitized gypsy moth larvae as detected by chromatographic assays. © 1996 Wiley-Liss, Inc.     

Development of the polyembryonic parasitoid Copidosoma floridanum in Trichoplusia ni

Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) parasitized by the polyembryonic egg-larval parasitoid Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) attained significantly larger final weights and head capsule widths than unparasitized controls. The difference in weight between parasitized and unparasitized hosts was not entirely accounted for by the weight of the C. floridanum brood. The head capsule widths of all parasitized and unparasitized fifth instars used in the study exceeded the critical threshold of 1.66 mm previously established for T. ni metamorphosis. The critical ratios associated with each T. ni instar of: 1) maximum weight within the instar:head capsule width and 2) maximum weight within the instar:weight at the beginning of the instar differed between parasitized and unparasitized larvae. Development of C. floridanum was synchronized with that of its host. Germ band formation and gastrulation of morulae destined to produce reproductive larvae invariably coincided with the host molt to the ultimate, fifth instar. Reproductive larvae had two instars. Eclosion from the egg to the first instar occurred during day 2 of the host's fifth instar, and ecdysis from the first to the second instar was synchronized with host cocoon spinning. Conversely, embryogenesis of morulae destined to produce precocious larvae began during the host first instar, continued through the second and third instar and ceased during the penultimate, fourth instar. Precocious larvae never molted and died when the host was consumed by the reproductive larvae.

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Résumé T. ni Hübner parasité par le parasitoïde ovo-larvaire C. floridanum Ashmead à développement polyembryonnaire atteint un poids final signficativement plus élevé avec une capsule céphalique plus grosse que les témoins non parasités, sans subir de mues surnuméraires. La différence de poids entre noctuelles parasitées ou non ne correspondait pas entièrement au poids des C. floridanum. Les largeurs des capsules céphaliques de tous les T. ni du cinquième stade dépassaient toutes le seuil critique de 1,66 mm lié à la métamorphose, mais les seuils critiques de taille du corps:largeur de la capsule céphalique et/ou taille et corps, taille initiale du corps au début du stade associé à la mue, différaient chez T. ni parasités ou non. Les développements de T. ni et de C. floridanum étaient synchrones. La formation de la bande germinative et la gastrulation de la morula produisant la multiplication des larves ont coïncidé invariablement avec la mue de l'hôte donnant le dernier stade. Les larves polyembryonnaires ont présenté deux stades. L'éclosion des oeufs s'est produite le deuxième jour du cinquième stade de T. ni, et le passage du premier au second était synchrone de la formation du cocon de l'hôte. Réciproquement, l'embryogenèse de la morula qui donnait des larves précoces commençait pendant le premier stade de l'hôte et se poursuivait à travers les second et troisième, pour cesser pendant le quatrième et pénultième stade.

     

Host plant species affects the quality of the generalist Trichoplusia ni as a host for the polyembryonic parasitoid Copidosoma floridanum

Diet of herbivorous insects can influence both the herbivores and their natural enemies. We examined the direct and indirect effects of diet on the interactions between the polyphagous herbivore Trichoplusia ni Hübner (Lepidoptera: Noctuidae) and its polyembryonic parasitoid Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae). To determine how host plant species and host plant iridoid glycoside content affect host caterpillars and their parasitoids, parasitized and unparasitized T. ni were given leaves of either Plantago lanceolata L., which contains the iridoid glycosides aucubin and catalpol, Plantago major L. (Plantaginaceae), which contains only aucubin, or Taraxacum officinale F.H. Wigg (Asteraceae), which contains neither. Survival of unparasitized T. ni was much lower when fed P. major compared with the other two host plants, whereas pupae were smallest when fed T. officinale and developed most slowly when fed P. lanceolata as larvae. Neither aucubin nor catalpol were detected in intact Plantago‐fed T. ni larvae or their hemolymph, and only trace amounts of aucubin were detected in frass, suggesting that these compounds are mostly metabolized in the midgut and are not encountered by the parasitoid. Copidosoma floridanum clutch size was almost doubled when reared from P. lanceolata‐fed T. ni compared with T. officinale‐fed larvae and tripled compared with P. major‐fed larvae, although the percent of parasitoids surviving to adulthood was uniformly high regardless of host diet. The observed variation in C. floridanum fitness among host diets is likely mediated by the effect of the diets on host quality, which in turn may be influenced more by other factors in the host plants than their iridoid glycoside profiles. Interactions between plant metabolites, generalist herbivores like T. ni, and their parasitoids may be predominantly indirect.     

Parasitoid-host endocrine relations: self-reliance or co-optation?

High titers of juvenile hormone (JH) maintain developmental arrest in Manduca sexta larvae parasitized by Cotesia congregata. Parasitized hosts exhibit up to 9.5 times greater amounts of total hemolymph JH (from 0.6±0.09 to 2.51±0.43 ng/ml) compared to non-parasitized controls. Elevated titers are observed throughout the fifth instar, even beyond egression of the parasitoids on day 5. GC–MS analysis revealed that in hemolymph of unparasitized control larvae, JH I is the major homolog and levels of JH III are negligible; in parasitized individuals the amounts of JH I, II, and III rise, and JH III predominates. Neck ligation ensured separation of M. sexta’s corpora allata from the posterior section, which contained most of the parasitoids in the infected insects. When the posterior region was sampled, JHs were not detected in the non-parasitzed larvae, but in those parasitized, JH III was found (1.98±0.29 ng/ml, 24 h post-ligation). JH III was the only homolog produced and secreted by the parasitoid in in vitro culture. This is the first report stating that a parasitoid secretes JH III and may contribute, at least in part, to the circulating titer in the host hemocoel, concurrently promoting host production of JH I and II.     

In vivo fluctuation of JH,JH acid,and ecdysteroid titer,and JH esterase activity,during development of fifth stadium Manduca sexta

Juvenile hormone (JH), JH acid, and ecdysteroid titer, and JH esterase activity, were measured in hemolymph from synchronous last stadium larvae of Manduca sexta. JH and JH acids were identified and quantified by GC-MS: JH I and II (and the corresponding acids) were the predominant JH homologs detected in males or females. Maximum levels of JHs and JH acids were observed just following ecdysis to the fifth (last) stadium (day 0, 0 hr) and at the prepupal stage (day 6–day 7). JH titer (≥ 1 ng JH I or II/ml) was higher than JH acid titer (∼0.7 ng JH I acid or JH II acid/ml) in very early fifth stadium larvae. However, this was reversed at the prepupal stage when higher titers of JH acids than JH were observed. JH acid titer began to rise prior to JH titer at the prepupal stage. JH esterase activity rose significantly only after JH or JH acid titers had begun to decline; maximum JH esterase activity was observed at day 3 and day 8. Ecdysteroid titer (measured by RIA) decreased during the last larval molt to a low level by day 0 (0 hr) and to undetectable levels at day 0 (12 hr) of the fifth stadium, by which time JH and JH acid levels had also declined substantially. Just prior to wandering, a small ecdysteroid peak was noted and a slightly elevated level of ecdysteroid was maintained for a further 2 days before a surge in ecdysteroid titer occurred at the prepupal stage, in synchrony with JH and JH acid titer maxima. There was no sexual dimorphism in timing or magnitude of JH, JH acid, and ecdysteroid titer or JH esterase activity.     

Differential induction of plant chemical defenses by parasitized and unparasitized herbivores: consequences for reciprocal,multitrophic interactions

Insect parasitoids can play ecologically important roles in virtually all terrestrial plant–insect herbivore interactions, yet whether parasitoids alter the defensive traits that underlie interactions between plants and their herbivores remains a largely unexplored question. Here, we examined the reciprocal trophic interactions among populations of the wild cabbage Brassica oleracea that vary greatly in their production of defensive secondary compounds – glucosinolates (GSs), a generalist herbivore, Trichoplusia ni, and its polyembryonic parasitoid Copidosoma floridanum. In a greenhouse environment, plants were exposed to either healthy (unparasitized), parasitized, or no herbivores. Feeding damage by herbivores induced higher levels of the indole GSs, glucobrassicin and neoglucobrassicin, but not any of the other measured GSs. Herbivores parasitized by C. floridanum induced cabbage plants to produce 1.5 times more indole GSs than levels induced by healthy T. ni and five times more than uninduced plants. As a gregarious endoparasitoid, C. floridanum causes its host T. ni to feed more than unparasitized herbivores resulting in increased induction of indole GSs. In turn, herbivore fitness parameters (including differential effects on male and female contributions to lifetime fecundity in the herbivore) were negatively correlated with the aliphatic GSs, sinigrin and gluconapin, whereas parasitoid fitness parameters were negatively correlated with the indole GSs, glucobrassicin and neoglucobrassicin. That herbivores and their parasitoids appear to be affected by different sets of GSs was unexpected given the intimate developmental associations between host and parasitoid. This study is the first to demonstrate that parasitoids, through increasing feeding by their herbivorous hosts, can induce higher levels of non‐volatile plant chemical defenses. While parasitoids are widely recognized to be ubiquitous in most terrestrial insect herbivore communities, their role in influencing plant–insect herbivore relationships is still vastly underappreciated.     

Immunoanalysis of unique protein in Trichoplusia ni larvae parasitized by the braconid wasp Chelonus near curvimaculatus

Parasitization in insects brings about profound biochemical and physiological effects in the host which may include complete overriding of the normal endocrinological program, resulting in precocious metamorphosis and in blockage of pupal development. The subtle effects of parasitization include changes in the expression of hemolymph proteins and the appearance of proteins which are unique to parasitized hosts. One such protein has been identified in the hemolymph of Trichoplusia ni larvae parasitized by the braconid wasp Chelonus near curvimaculatus. In this study, purified preparations of the parasitism-specific protein were used to generate polyconal antibodies against the protein. Results from the immunocharacterization indicate the antibodies obtained are highly specific for the protein and are present in a high titer (1:8000 antiserum dilution yielded strong signals in analysis of the protein in 0.25 μl hemolymph). Subsequently, the expression of the parasitism-specific protein in the hemolymph and tissues was analyzed by immunoblotting during the entire course of development in normal and parasitized insects. The parasitism-specific protein was not detected in normal, unparasitized larvae. In parasitized insects, expression of the parasitism-specific protein appears to be stage-specific in that it is only detected during the last larval stadium of precociously metamorphosing larvae, but is absent from all earlier stages of development.     

Effects of parasitization of Trichoplusia ni by Chelonus sp.

ABSTRACT. Parasitization of Trichoplusia ni (Huebner) (Lepidoptera: Noctuidae) by Chelonus sp. (Hymenoptera: Braconidae), an egg-larval parasitoid, leads to precocious cocoon spinning of the host in the fourth (penultimate) stadium followed by parasitoid emergence from the prepupa. We have investigated the mechanism by which Chelonus sp. disrupts host development. The developing larva and fluids injected by the adult female separately from the egg, are not the source of these effects, but it remains a possibility that the teratocytes, originating from the trophamnion of the parasitoid egg, are responsible. The titre of the juvenile hormone esterase activity in the haemolymph of the parasitized fourth instar host is similar to that in the initial period of the final instar of normal T. ni, but lacks the postwandering peak of activity. The increased JHE activity leads to a reduced JH titre early in the fourth stadia. This indicates that disruption of host development occurs within 12h after apolysis to the fourth stadium, if not before. Anti-juvenile hormone activity is not detected in extracts of parasitized T. ni. The morphological and behavioural changes associated with precocious development of the T. ni host are prevented by applications of juvenile hormone I, juvenile hormone II and the juvenoid, Ro 10–3108, but not juvenile hormone III and the juvenoid R 20458. However, these applications fail to prevent the onset of juvenile hormone esterase activity, another marker of precocious development. These observations indicate that simple anti-juvenile hormone activity may not be the mechanism of disruption of host development. Development of the parasitoid is disrupted by application of Ro 10–3108 and juvenile hormones I, II and III, but timing of eclosion is only affected by application of juvenile hormone I, juvenile hormone II and Ro 10–3108. This observation may indicate a discrimination by the parasitoid between its own juvenile hormone III and the host's juvenile hormone II.     

Detrimental effects of plant compounds on a polyembryonic parasitoid are mediated through its highly polyphagous herbivore host

Plant defensive compounds can have sometimes severe deleterious effects on both herbivores and their natural enemies. Iridoid glycosides (IGs) are defensive compounds that are well established as deterrent to several generalist herbivores and generalist predators. Trichoplusia ni Hübner (Lepidoptera: Noctuidae) is exceptional among generalist herbivores for its ability to tolerate and thrive when feeding upon IG‐producing plant species; however, it is not known whether the compounds themselves have a harmful effect on T. ni and whether the effects in turn affect its oligophagous endoparasitoid Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae). To examine these effects, a semi‐purified extract of the IG‐containing plant Plantago lanceolata L. (Plantaginaceae), containing the IGs aucubin and catalpol, was added to artificial diets at 0, 1, 5, or 10% diet dry weight. These diets were fed to both C. floridanum‐parasitized and unparasitized T. ni. Diets higher in IGs tended to be more toxic to both parasitized and unparasitized larvae: host larvae that did survive were slightly smaller and took longer to develop on higher IG diets and total clutch size and survival of the parasitoid C. floridanum were greatly reduced as the host's dietary intake of IGs increased. Only small amounts of aucubin were detected inside the T. ni hemocoel, suggesting that the negative effect of these compounds on C. floridanum is due to nutritional quality of the host being reduced rather than direct toxic effects of the compounds.     

Hydrocarbon accumulation and lipid biosynthesis during larval development in the cabbage looper,Trichoplusia ni

Larvae of the cabbage looper, Trichoplusia ni, were analyzed for the accumulation and biosynthesis of cuticular and internal hydrocarbon at closely spaced and accurately timed intervals during the fourth and fifth stadia. Large differences in the incorporation of [1-¹⁴C]acetate into hydrocarbon were observed at different times during larval development. Much higher incorporation was observed during feeding stages as compared to wandering stages, while lowest rates of biosynthesis occurred just prior to ecdysis. Fourth stadia wanderers accumulated increased amounts of internal hydrocarbon, which is apparently used to cover the newly forming cuticle. During the fourth to fifth stadium moult insects lost all cuticular hydrocarbon that was present on the old cuticle (about 8 μg/insect) and had about 8 μg/insect on the surface of the newly exposed cuticle. During the fourth stadium incorporation of [1-¹⁴C]acetate into total lipid declined between feeding and wandering stages from 24% of injected radiolabel to 7%. Similar decreases in lipid biosynthesis were observed between feeders and wanderers in fifth stadium larvae with the greatest decrease found in the triacylglycerol fraction. These results document dramatic changes in the accumulation and biosynthesis of hydrocarbon and other lipids during larval development.     

Inhibition of testicular growth and development in Manduca sexta larvae parasitized by the braconid wasp Cotesia congregata

Tobacco hornworm larvae parasitized by the gregarious larval endoparasitoid Cotesia congregata exhibited an inhibition in testicular growth and development, the extent of which was determined by the age and developmental stage of the host at the time of parasitization. The degree of parasitic castration, as assessed by measurements of testicular volume, was correlated with the stadium in which parasitization occurred. A mathematical formula requiring the measurement of testicular length, width and depth was used to calculate testicular volume. The use of the depth parameter revealed a negative correlation between host weight and testicular volume in parasitized larvae. Testicular volumes of fifth instar hosts, which had been parasitized in the first stadium, were significantly smaller than those originally parasitized as fourth or fifth instar larvae and were not correlated with parasitoid load. Effects of natural parasitism were not duplicated by injections of C. congregata polydnavirus and venom, topical treatment with the juvenile hormone analog methoprene, or starvation of nonparasitized larvae. Larvae receiving virus plus venom or methoprene grew larger due to delayed wandering and had larger testes than controls. Deleterious effects on host testes may be due to the effects of nutrient competition between the developing parasitoid progeny and the gonads, combined with the juvenilizing effects believed to be caused by the polydnavirus.     

Relationships between the parasitoid Hyposoter exiguae and Trichoplusia ni: Parasitoid-induced histo- and cytopathology

The histology and cytology of Trichoplusia ni larvae were studied for evidence of abnormality or pathology induced by the solitary ichneumonid endoparasitoid, Hyposoter exiguae. Sample control and parasitized larvae were fixed every other day, and sections of these larvae were stained with mercuric-bromophenol blue. The fat body of parasitized larvae failed to show many of the changes characteristic of normally developing controls and, on the last day of parasitism, revealed extensive pathological changes. Spermatogenesis continued normally until the end of the association in parasitized hosts even though their development was halted in the fifth larval stadium. Parasitoid larvae seemed to secrete a proteinaceous material from their salivary and rectal glands into the host hemocoel. This material may be responsible for the pathological changes reported here. The parasitoids apparently fed on hemolymph alone until about 24 hr before emergence and pupation.     

Stage-specific effects of Campoletis sonorensis parasitism on Heliothis virescens development and prothoracic glands

Abstract The ichneumonid endoparasitoid Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae) injects a polydnavirus when it oviposits into a host. We compared the development of Heliothis virescens (F.) (Lepidoptera: Noctuidae) larvae parasitized in the penultimate (fourth) stadium with those parasitized in the last (fifth) stadium by C.sonorensis and show that hosts stung in the fifth stadium exhibited arrested or delayed development compared to the controls. Parasitoids developed normally to the point of emergence in larvae stung in the fifth stadium but most did not successfully emerge from the host. The prothoracic glands in all successfully parasitized fifth stadium hosts and most unsuccessfully parasitized fifth stadium hosts showed some degree of virally-induced degeneration. Larvae stung in the fourth stadium developed more slowly than controls and either did not moult or developed to a fifth and sometimes a supernumerary sixth stadium before parasitoid emergence. Unsuccessfully parasitized hosts were delayed in their development but eventually moulted to the fifth and, in some cases, a supernumerary sixth stadium before pupating. Hosts stung in the fourth stadium showed no signs of prothoracic gland degeneration whether successfully parasitized or not. In addition, calyx fluid injections into early fourth stadium hosts did not cause prothoracic gland degeneration even after these hosts moulted to the fifth stadium, suggesting that degeneration induced by polydnavirus is specific to the last stadium of the host.     

The role of juvenile hormone in the larval diapause of the European corn borer,Ostrinia nubilalis

The possible role of juvenile hormone (JH) in the induction and termination of larval diapause in the European corn borer, Ostrinia nubilalis, was investigated using topical applications of both JH I and a JH mimic as well as by monitoring JH titers with the Galleria bioassay. Neither JH nor the JH mimic ZR515 was capable of influencing diapause termination when administered topically. The Galleria bioassay revealed little or no JH in the hemolymph of mid diapause (>30 days) insects, indicating no demonstrable role for JH in diapause maintenance. When ZR515 was administered to nondiapause, newly ecdysed fifth instar larvae the pupal molting cycle was delayed. By use of photoperiodic regimes we were able to show that the molting delay was not equivalent to diapause induction. The Galleria bioassay showed differences in JH titer profiles between diapause and nondiapause animals during the final larval stadium. The nondiapause insects showed titers that decline rapidly to trace amounts following the molt to fifth instar then rose prior to pupation. The diapause insects had generally higher titers and exhibited a more gradual decline after the molt. No evidence was obtained to support the hypothesis that JH plays a key role in the induction, maintenance, or termination of larval diapause.     

Inhibition of the larval ecdysis and emergence behavior of the parasitoid Cotesia congregata by methoprene

Parasitism of the tobacco hornworm, Manducasexta, by the braconid wasp Cotesiacongregata, induces developmental arrest of the host in the larval stage. During the final instar of the host, its juvenile hormone (JH) titer is elevated, preventing host metamorphosis. This study investigated the effects of hormonal manipulation of the host on the parasitoid’s emergence behavior. The second larval ecdysis of the wasps coincides with their emergence from the host, and application of the juvenile hormone analogue methoprene to day 4 fifth instar hosts either delayed or totally suppressed the subsequent emergence of the wasps. Effects of methoprene were dose-dependent and no parasitoids emerged following treatment of host larvae with doses >50 μg. Parasitoids which failed to emerge eventually succumbed as unecydsed pharate third instar larvae in the hemocoel of the host. Effects of host methoprene treatment on parasitoid metamorphosis were also assessed, and metamorphic disruption occurred at much lower dosages compared with doses necessary to suppress parasitoid emergence behavior. The inhibitory effect of methoprene on parasitoid emergence behavior appears to be mediated by effects of this hormone on the synthesis or release of ecdysis-triggering hormone (ETH) in the parasitoid, the proximate endocrine cue which triggers ecdysis behavior in free-living insects. ETH accumulated in the epitracheal Inka cells of parasitoids developing in methoprene-treated hosts, suggestive of a lack of hormone release. Thus, the hormonal modulation of parasitoid emergence behavior appears to be complex, involving a suite of hormones including JH, ecdysteroid, and peptide hormones.     

Endocrine alteration and precocious premetamorphic behaviors in the greater wax moth larvae,Galleria mellonella,parasitized by an endoparasitoid,Apanteles galleriae

Parasitization of Galleria mellonella (Lepidoptera: Pyralididae) larvae by a larval endoparasitoid Apanteles galleriae (Hymenoptera: Braconidae) leads to the precocious expression of premetamorphic behavior in the sixth (normally penultimate) instar host larvae prior to the parasitoid's emergence. We investigated the role of parasitization with A. galleriae on the alteration of development and/or behavior of its host. The ecdysteroid titer in the hemolymph of parasitized sixth instar larvae (the last instar of parasitized larvae) was higher than that of unparasitized ones, and the high ecdysteroid concentrations induced premetamorphic behaviors such as wandering and cocoon spinning. However, the epidermis of the parasitized larvae was not pupally committed through this stage. The activity of JH esterase in the parasitized larvae remained low, and application of a JH analogue to these larvae caused the production of a larval-type cocoon. These facts suggest that the parasitization by A. galleriae induces precocious premetamorphic behaviors of G. mellonella larvae by changing host endocrine conditions without causing the typical larval-pupal metamorphosis. Arch. Insect Biochem. Physiol. 34:257–273, 1997. © 1997 Wiley-Liss, Inc.     

Endokrinologische Untersuchungen an dem Wirt-Parasit-System: Pieris brassicae-Apanteles glomeratus

Die von Apanteles glomeratus L. parasitierten Raupen von Pieris brassicae zeigen in Abhängigkeit des Parasitierungstermins eine deutliche Veränderung des Juvenilhormon (JH)-Titer-Verlaufs während des letzten Larvenstadiums. Dabei tritt ein steiler Anstieg des JH-Gehaltes der Wirtshämolymphe im Zusammenhang mit der Häutung der Parasitenlarven vom 1. zum 2. Larvenstadium auf. Aufgrund von Ligations-experimenten konnte nachgewiesen werden, daß die Parasitenlarven selbst für den erhöhten JH-Titer ihrer Wirtsraupen verantwortlich sind, indem sie während ihrer Häutungsphase anscheinend JH in die Wirtshämolymphe abgeben.Eine durch die Parasitierung gesteigerte Syntheseaktivität läßt sich aus den Befunden histologischer Schnitte der Corpora allata frühparasitierter Raupen nicht feststellen. Dagegen weisen die Prothoraxdrüsen parasitierter Raupen zur Mitte des letzten Stadiums eine deutlich kleinere Querschnittsfläche auf als unparasitierte Tiere. Eine dadurch im Zusammenhang mit dem erhöhten JH-Titer bestehende Beziehung zur Häutungsunfähigkeit parasitierter Pieris-Raupen am Ende des letzten Larvenstadiums wird diskutiert.

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Summary The effects of parasitism by Apanteles glomeratus on the hemolymph juvenile hormone (JH) titers of Pieris brassicae during the last larval instar were determined using the Galleria bioassay.Depending on the time of parasitization, a significant increase of the JH titer could be observed when moulting of the parasites from the first to the second larval instar occurred.As neck-ligatured, parasitized Pieris larvae showed a similar increase of the JH titer at this time, it is concluded that the parasite larvae themselves are responsible for the elevation of the titer by delivering JH during their ecdysis into the host's hemolymph.This is supported by histological results from the corpora allata of parasitized and unparasitized caterpillars at the first and third day of the last larval instar, indicating no differences in its secretory activity. The prothoracid glands of parasitized host larvae, however, appear significantly smaller than those of comparable unparasitized ones in the middle of the last instar. A reduced secretory activity at this time, which is assumed from their decreased size, combined with an elevated JH titer may explain why parasitized larvae fail to moult at the end of their larval development.

     

Parasitism-induced hemolymph polypeptides in Manduca sexta (L.) larvae parasitized by the braconid wasp Cotesia congregata (Say)

Parasitization of newly ecdysed third, fourth, or fifth instar Manduca sexta larvae by the gregarious braconid wasp Cotesia congregata induces synthesis of new hemolymph proteins in the host. Analysis of hemolymph from parasitized and unparasitized control larvae using SDS gel electrophoresis showed that a major 33 kd band, plus several minor bands, were synthesized in parasitized but not control larvae; autoradiograms of proteins labeled in vivo for 1 hr with [³⁵S]methionine indicated that synthesis of the 33 kd polypeptide began a few hours following oviposition by the wasp. Synthesis of the 33 kd parasitism-specific polypeptide was induced in unparasitized larvae by the injection of ovarian calyx fluid from adult female wasps; this fluid is known to contain two morphologically distinct types of virus particles that are normally injected into the host along with eggs during parasitization. Exposure of calyx fluid to psoralen in the presence of long-wave u.v. light destroyed its capacity to induce synthesis of the 33 kd protein, suggesting that synthesis of this polypeptide may be mediated by viral nucleic acid.     

Ecdysone metabolism in the host-parasitoid-system Trichoplusia ni/Chelonus sp

In unparasitized 4th and 5th-instar larvae of Trichoplusia ni and in 4th-instar larvae parasitized by Chelonus sp. 20-hydroxyecdysone, 20,26-dihydroxyec-dysone, and 20-hydroxyecdysonoic acid were the predominant metabolites formed 2 h after injection of [³H]ecdysone. Other unidentified metabolites were seen, but none seemed to be specific for either parasitized or unparasitized larvae. The major difference between parasitized and unparasitized larvae was seen with respect to the quantity of apolar (unidentified) and polar metabolites (20-hydroxyecdysonoic acid and unidentified ones), which were produced to a greater extent in parasitized larvae. Ecdysone was rapidly converted into 20-hydroxyecdysone and the other polar metabolites in all stages investigated, and the parasitoid seemed not to affect the conversion of ecdysone into 20-hydroxyecdysone. When analyzing the fate of [³H]ecdysone in host and parasite separately, at a stage when the parasite drinks hemolymph of its host, we observed that 10–20% of the radioactivity was recovered from the parasitoid. Analysis of the parasitoid's ecdysteroids revealed that ecdysone and 20-hydroxyecdysone represented only a small proportion of the recovered labeled ecdysteroids, the majority being apolar and polar metabolites. Our data suggest that the parasitoid takes up ecdysteroids from its host, converts them, and to some extent releases apolar metabolites into the host.