Chelonus Inanitus Research Articles

Improved reproduction of Chelonus inanitus on Ephestia kuehniella highlights this factitious host as an alternative to the natural host Spodoptera littoralis

Chelonus inanitus L. (Hymenoptera: Braconidae) is an egg-larval parasitoid of Lepidoptera, with the potential for biological control of noctuids. The lack of information merits research on its reproductive and developmental biology. We studied the reproduction of mated parasitoid pairs during female lifetime and the development of the progeny on two hosts, the factitious Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and the natural Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae). The longevity of pairs subjected or not to parasitism was compared. Development of the progeny after parasitization and growth rates were studied. Reproduction decreased the longevity of both sexes in every host. The similar survival patterns proved that sex was not a factor influencing longevity. Females parasitized immediately after emergence and offspring production peaked at 2–2.5 days. Low parasitization rates (3–12%) were generally observed. Reproduction on S. littoralis was fourfold less efficient, probably due to failure of immature stages leading to poor progeny. Sex ratio of the progeny was mostly male-biased. Males developed faster in both hosts. Development was 20 days shorter in the natural host. Strikingly, the parasitoid performed successfully better on the factitious host. Inbreeding, poor understanding of host preference, and inadequate rearing and handling practices are discussed as possible causes of the worse parasitoid performance on S. littoralis.

Chelonus inanitus bracovirus encodes lineage-specific proteins and truncated immune IκB-like factors.

Bracoviruses and ichnoviruses are endogenous viruses of parasitic wasps that produce particles containing virulence genes expressed in host tissues and necessary for parasitism success. In the case of bracoviruses the particles are produced by conserved genes of nudiviral origin integrated permanently in the wasp genome, whereas the virulence genes can strikingly differ depending on the wasp lineage. To date most data obtained on bracoviruses concerned species from the braconid subfamily of Microgastrinae. To gain a broader view on the diversity of virulence genes we sequenced the genome packaged in the particles of Chelonus inanitus bracovirus (CiBV) produced by a wasp belonging to a different subfamily: the Cheloninae. These are egg-larval parasitoids, which means that they oviposit into the host egg and the wasp larvae then develop within the larval stages of the host. We found that most of CiBV virulence genes belong to families that are specific to Cheloninae. As other bracoviruses and ichnoviruses however, CiBV encode v-ank genes encoding truncated versions of the immune cactus/IκB factor, which suggests these proteins might play a key role in host-parasite interactions involving domesticated endogenous viruses. We found that the structures of CiBV V-ANKs are different from those previously reported. Phylogenetic analysis supports the hypothesis that they may originate from a cactus/IκB immune gene from the wasp genome acquired by the bracovirus. However, their evolutionary history is different from that shared by other V-ANKs, whose common origin probably reflects horizontal gene transfer events of virus sequences between braconid and ichneumonid wasps.

Comparison of the Parasitization of Chelonus inanitus L. (Hymenoptera: Braconidae) in Two Spodoptera Pests and Evaluation of the Procedure for Its Production.

Simple SummarySuccessful integrated pest management of horticultural crops requires the evaluation of natural enemies used in biological control. To improve the mass rearing of Chelonus inanitus (L.) in the factitious host Ephestia kuehniella Zeller, we investigated the influence of host age and number of females parasitizing simultaneously on quality parameters evaluated in the commercial production of biological control agents, such as overall rearing success, duration of life cycle and body size. Under semi-field conditions, we investigated how the competition among females impacted the parasitism success on important pests Spodoptera exigua (Hübner) and S. littoralis (Boisduval). For the parasitoid mass rearing optimization, mature eggs seem to be more convenient because they increased the female percentage in the offspring and shortened the parasitoid life cycle. Furthermore, a high number of females parasitizing simultaneously reduced the emergence of non-parasitized hosts. Under more realistic conditions, the parasitoid effectively controlled both pests, but S. exigua may be a more convenient host because the parasitoid offspring was much larger. With this research, we provide a foundation that aims to better manage these cosmopolitan, highly polyphagous pests that exhibit long-distance migratory potential, alongside the potential use of this natural enemy.Chelonus inanitus (L.) is an egg-larval parasitoid of noctuids Spodoptera exigua (Hübner) and S. littoralis (Boisduval), whose mass rearing or real potential has not been targeted yet. To improve the rearing in the factitious host Ephestia kuehniella Zeller, we investigated the influence of host age and number of females parasitizing simultaneously on the overall rearing success, the influence of host age on the life cycle, and the influence of host species on the parasitoid body size. The proportion of emerging C. inanitus was higher from young host eggs, but more females emerged from mature eggs. Under high parasitoid competition, we observed a reduction in non-parasitized hosts without reducing parasitoid emergence. The parasitoid life cycle was longer in females, but the mismatch between sexes was smaller in mature eggs. The parasitoid size was smaller in the factitious host than in the natural hosts. Under semi-field conditions, we investigated the competition among parasitoid females on the overall parasitism success. The reproductive parasitism was more successful in S. exigua than in S. littoralis, and the maximum emergence was reached with three and four females, respectively. The control of S. littoralis may be attributed to the high developmental mortality, a non-reproductive parasitism that is often underestimated.

Host recognition by the egg–larval parasitoid Chelonus inanitus: effects of physical and chemical cues

AbstractParasitoid wasps are widely used as biocontrol agents. For successful deployment, it is important to know how they search for and recognize their hosts. They often use chemical cues in host searching and recognition. Little attention has been paid to the use of physical cues, particularly when combined with chemical cues, though a combination of cues may improve searching efficiency. Chelonus inanitus L. (Hymenoptera: Braconidae) is a solitary, egg–larval parasitoid wasp that parasitizes various lepidopteran species, including serious crop pests. In this study, effects of physical and/or chemical cues on host recognition were investigated in C. inanitus by observing its antennal searching, ovipositor probing, and the duration of arrestment. In a physical cue test, egg‐mass models with glass beads differing in size were used, and a single‐egg model with a specific size of bead. Egg‐mass models with beads of 0.4–1.0 mm in diameter arrested C. inanitus, in accordance with egg size and arrangement of the host. In a chemical cue test, extract from egg masses of the host Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), equivalent to half of a host egg mass and extract diluted 100‐fold were used, and the undiluted extract stimulated C. inanitus. Untreated egg‐mass models (0.2‐mm‐diameter glass beads) and diluted egg extract arrested C. inanitus less effectively; however, when glass beads were treated with the diluted extract, arrestment increased to the same degree as the undiluted extract. These results suggest that C. inanitus uses both physical and chemical cues to recognize eggs of its host, S. litura, and that these stimuli act synergistically.

Effect of granulovirus infection of Spodoptera litura (Lepidoptera: Noctuidae) larvae on development of the endoparasitoid Chelonus inanitus (Hymenoptera: Braconidae)

Infection of parasitized Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae by a granulovirus (GV) deleteriously affected the development of the endoparasitoid Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae). When second-instar parasitized S. litura larvae were inoculated with GV, the percentages of emergence, pupation, and adult eclosion of C. inanitus were significantly lower from GV-infected hosts than those from uninfected ones. Lower parasitoid emergence was due to the earlier death of parasitized and GV-infected hosts and slower development of parasitoid larvae in GV-infected hosts than in uninfected ones. Some of the parasitoid larvae that emerged from GV-infected hosts died before pupation and adult eclosion as a result of lower external feeding on GV-infected cadavers. Furthermore, the body volume of parasitoids developing in GV-infected hosts was significantly lower than that of parasitoids developing in uninfected hosts. The experiment in which host cadavers and emerged parasitoids were switched revealed that external feeding of parasitoids was affected both by infection of host cadavers with GV and also by parasitoid development within GV-infected hosts. Our data show that GV infection of S. litura larvae has deleterious effects on C. inanitus development.

Kaolin and copper-based products applications: Ecotoxicology on four natural enemies

Lethal and sublethal effects of kaolin clays and two copper-based products on four natural enemies found in olive orchards Anthocoris nemoralis (F.) (Hem. Anthocoridae), Chelonus inanitus (L.) (Hym. Braconidae), Chilocorus nigritus (F.) (Col. Coccinellidae) and Scutellysta cyanea Motschulsky (Hym. Pteromalidae) are described. Both kaolin and copper can be applied for controlling the olive fruit fly and the olive moth, two important pests of this crop.The products did not increase the mortality of any of the insects studied, with the exception of A. nemoralis. The sublethal effects, however, differed depending on the parameter evaluated and the insect studied. Both kaolin and coppers slightly, but significantly, reduced the life span of C. inanitus and S. cyanea. Number of eggs laid by A. nemoralis females were reduced, but not significantly compared to the controls. In the behavioural experiments, clear preference for remaining on kaolin-untreated surfaces when insects were able to choose was observed.Despite having some negative effects, the negative impact on natural enemies was lower than the impact caused by products commonly applied in this crop against the pests stated above. Therefore, both kaolin and copper can be considered as alternative products to be applied in olive orchards if an effective resistance management programme is to be developed. Furthermore, both of them are allowed in organic farming, in which the number of products that can be applied is more restricted.

The venom composition of the parasitic wasp Chelonus inanitus resolved by combined expressed sequence tags analysis and proteomic approach

BackgroundParasitic wasps constitute one of the largest group of venomous animals. Although some physiological effects of their venoms are well documented, relatively little is known at the molecular level on the protein composition of these secretions. To identify the majority of the venom proteins of the endoparasitoid wasp Chelonus inanitus (Hymenoptera: Braconidae), we have randomly sequenced 2111 expressed sequence tags (ESTs) from a cDNA library of venom gland. In parallel, proteins from pure venom were separated by gel electrophoresis and individually submitted to a nano-LC-MS/MS analysis allowing comparison of peptides and ESTs sequences.ResultsAbout 60% of sequenced ESTs encoded proteins whose presence in venom was attested by mass spectrometry. Most of the remaining ESTs corresponded to gene products likely involved in the transcriptional and translational machinery of venom gland cells. In addition, a small number of transcripts were found to encode proteins that share sequence similarity with well-known venom constituents of social hymenopteran species, such as hyaluronidase-like proteins and an Allergen-5 protein.An overall number of 29 venom proteins could be identified through the combination of ESTs sequencing and proteomic analyses. The most highly redundant set of ESTs encoded a protein that shared sequence similarity with a venom protein of unknown function potentially specific of the Chelonus lineage. Venom components specific to C. inanitus included a C-type lectin domain containing protein, a chemosensory protein-like protein, a protein related to yellow-e3 and ten new proteins which shared no significant sequence similarity with known sequences. In addition, several venom proteins potentially able to interact with chitin were also identified including a chitinase, an imaginal disc growth factor-like protein and two putative mucin-like peritrophins.ConclusionsThe use of the combined approaches has allowed to discriminate between cellular and truly venom proteins. The venom of C. inanitus appears as a mixture of conserved venom components and of potentially lineage-specific proteins. These new molecular data enrich our knowledge on parasitoid venoms and more generally, might contribute to a better understanding of the evolution and functional diversity of venom proteins within Hymenoptera.

Identification of bracovirus particle proteins and analysis of their transcript levels at the stage of virion formation

Polydnaviruses (PDVs) are unique symbiotic viruses associated with parasitic wasps; they replicate only in the calyx cells of a wasp's ovaries and are transferred at oviposition along with the parasitoid egg into the lepidopteran host. The DNA packaged in the viral particles encodes factors that manipulate the host's immune defences and development to benefit the parasitoid. PDVs are found in two subfamilies of ichneumonids (ichnoviruses) and in braconids of the microgastroid complex (bracoviruses). We recently showed that the latter derive from an ancestral nudivirus, as 24 nudivirus-related genes were identified in ovaries of two distantly related braconids at the stage of virion formation. Here, we present a comprehensive analysis of the viral particle proteins of the Chelonus inanitus bracovirus (CiBV). Proteins of purified CiBV particles were analysed by mass spectrometry and amino acid sequences matched to the existing ovarian-cDNA database. In addition, transcript quantities of identified genes were measured by quantitative real-time PCR in female pupae at the onset and peak of virion formation and at corresponding stages in male pupae. This combined approach allowed the identification of 44 CiBV particle proteins: 16 were nudivirus-related, three had similarity to ovarian proteins of another braconid, 11 had similarity to cellular proteins and 14 had no similarity to known proteins. The transcripts of all of them increased in female, but not male, pupae. These data confirm the important contribution of nudivirus genes but also indicate the presence of many lineage- or species-specific proteins possibly involved in the parasitoid-host interaction.

Does risk of egg parasitism affect choice of oviposition sites by a moth? A field and laboratory study

Abstract In many insects the eggs are highly vulnerable and egg parasitism can represent a major cause of mortality. It is thus important for the ovipositing female to find a protected site for her eggs. We have examined how egg parasitation can affect host plant choice by Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). Ovipositing moths exhibited significantly higher preference for alfalfa compared to cotton, both in the laboratory and the field. However, larval performance, in terms of development rate and the attained larval and pupal weight, was significantly better on cotton than on alfalfa. In laboratory tests no difference in larval survival on the two host plants was observed. To test the hypothesis that seeking enemy-free space could be a factor behind the preference for alfalfa, the parasitation levels on the two plants were investigated. In field tests, the egg parasitoid Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) parasitized a significantly higher number of egg batches on cotton than on alfalfa. Furthermore, the parasitoid was significantly faster in finding and parasitizing S. littoralis eggs on cotton than on alfalfa in a cage experiment. These findings support the assumption that the preference for the inferior larval food plant, alfalfa, reflects a search for a host plant species on which attacks by natural enemies are less likely. Possible factors accounting for the preference of S. littoralis for alfalfa and the higher parasitation rates on cotton are discussed.

Venom of the egg-larval parasitoid Chelonus inanitus is a complex mixture and has multiple biological effects

The egg-larval parasitoid Chelonus inanitus injects bracoviruses (BVs) and venom along with the egg into the host egg; both components are essential for successful parasitoid development. All stages of eggs of its natural host, Spodoptera littoralis, can be successfully parasitized, i.e. from mainly a yolk sphere to a fully developed embryo. Here, we show that the venom contains at least 25 proteins with masses from 14 kDa to over 300 kDa ranging from acidic to basic. The majority is glycosylated and their persistence in the host is short when old eggs are parasitized and much longer when young eggs are parasitized. Physiological experiments indicated three different functions. (1) Venom synergized the effect of BVs in disrupting host development when injected into third instar larvae. (2) Venom had a transient paralytic effect when injected into sixth instar larvae. (3) In vitro experiments with haemocytes of fourth instar larvae suggested that venom alters cell membrane permeability. We propose that venom promotes entry of BVs into host cells and facilitates placement of the egg in the embryo's haemocoel when old eggs are parasitized. The multifunctionality of the venom might thus be essential in enabling parasitization of all stages of host eggs.

Stage dependent influences of polydnaviruses and the parasitoid larva on host ecdysteroids

In the solitary egg–larval parasitoid Chelonus inanitus (Braconidae) both polydnavirus and the parasitoid larva manipulate host development. Parasitization leads to a premature drop in juvenile hormone titre and a precocious onset of metamorphosis in the 5th larval instar. The C. inanitus bracovirus (CiBV) alone causes a reduction in host ecdysteroid titres at the pupal cell formation stage and prevents pupation. Here we report three new findings. (1) We show that parasitization causes a reduction in haemolymph ecdysteroid titre immediately after the moult to the 5th instar; similarly low values were seen in nonparasitized larvae after the moult to the 6th instar. These data along with parasitoid removal experiments indicate that the low ecdysteroid titre after the moult is a very early sign of the upcoming metamorphosis. (2) In vitro experiments with prothoracic glands and brain extracts showed that CiBV affects both prothoracic glands and prothoracicotropic hormone after the stage of pupal cell formation. (3) In the haemolymph of parasitized larvae the ecdysteroid titre increased in the late cell formation stage, i.e. immediately before egression of the parasitoid. In vitro experiments showed that late 2nd instar parasitoids release ecdysteroids and are thus very likely responsible for the rise in host ecdysteroids.

The immature stages of Chelonus inanitus (L.), a parasite of the Cotton Leafworm, Spodoptera littoralis (BOISD.), in Egypt (Hym., Braconidae)

The braconid parasite Chelonus inanitus (L.) seems to be one of the most efficient parasites of the cotton leafworm, Spodoptera littoralis (BOISD.) in Egypt at present. The nomenclature of the species is discussed and apparently three specific names seem to be synonyms for the parasite. The name C. inanitus is applied in the present work because it is more common in the region and until further taxonomic studies prove the occurrence of a more correct name for the species. The parasite was reared in the laboratory on S. littoralis and Ephestia kuehniella. Laboratory rearings of E. kuehniella and of the parasite are described. The ovarian and deposited eggs, three instar larvae, prepupa, cocoon, and pupa are deseribed in some detail and illustrated.

Transcriptional analysis of polydnaviral genes in the course of parasitization reveals segment‐specific patterns

Polydnaviruses are symbiotic viruses of endoparasitic wasps, which are formed in their ovary and injected along with the eggs into the host. They manipulate the host in a way to allow successful parasitoid development. A hallmark of polydnaviruses is their segmented genome consisting of several circles of double-stranded DNA. We are studying the solitary egg-larval parasitoid Chelonus inanitus (Braconidae) parasitizing Spodoptera littoralis (Noctuidae). The polydnavirus of Chelonus inanitus (CiV) protects the parasitoid larva from encapsulation by the host's immune system, slightly modifies host nutritional physiology, and induces a developmental arrest of the host in the prepupal stage. Here we present data on newly identified CiV genes and their expression patterns in the course of parasitization. None of these genes has similarity to other genes and so far no gene families could be found. A rough estimation of transcript quantities revealed that even the most highly expressed CiV genes reach maximal values, which are 250 times lower than actin. This indicates that the CiV-induced alterations of the host are brought about by a concerted action of low levels of transcripts. In an overview, we show the expression patterns of all CiV genes analysed up to now; they indicate that several genes with similar expression patterns (early, persistent, intermediate, or late) are grouped together on the same segment. This is the first observation of this type. It suggests that one function of the segmentation of the polydnavirus genome may be the grouping together of genes, which are regulated in a similar manner.

Genome organization of the Chelonus inanitus polydnavirus: excision sites, spacers and abundance of proviral and excised segments

Polydnaviruses are only found in symbiotic association with parasitic wasps within the families Ichneumonidae and Braconidae (ichnoviruses and bracoviruses). They have a segmented genome consisting of circular double-stranded DNA. In the proviral linear form they are integrated in the wasp's genome; in two bracoviruses, segments were found to be clustered. Proviral segments have direct terminal repeats. Segment excision has been proposed to occur through juxtaposition of these repeats by formation of a loop and recombination; one copy of the repeat then ends up in the circular segment and one in the rejoined DNA. Here we analysed the excision/circularization site of four segments of the Chelonus inanitus bracovirus (CiV) and found that they are similar to the two already known sites; on the basis of the combined data an extended excision site motif was found. Analyses of segment flanking sequences led to the first identification of one complete and several partial spacers between proviral segments in a polydnavirus. The spacer between the proviral segments CiV14 and CiV22.5 has a length of 2065 bp; the terminal repeats of CiV14 and CiV22.5 were seen to have an opposite orientation and from this a model on the spacial organization of the loops of the proviral cluster is proposed. Through various approaches it was shown that spacers are not excised or injected into the host. Measurement of relative abundances of various segments in proviral and excised form indicates for the first time that abundant segments are present in multiple copies in the proviral form.

The influence of two endoparasitic wasps, Hyposoter didymator and Chelonus inanitus, on the growth and food consumption of their host larva Spodoptera littoralis

The influence of parasitism by Hyposoter didymator (Thunberg; Hymenoptera: Ichneumonidae) and Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) on the growth and food consumption of their host Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) was studied in the laboratory. Parasitised larvae consumed significantly less artificial diet than unparasitised ones. Egg parasitisation by C. inanitus affected host larval consumption from the second day after emergence and it was significantly different from that of unparasitised ones. H. didymator, however, started to reduce larval consumption 4 days after parasitisation on the third instar host larvae. The overall reduction achieved by the larval endoparasitoid H. didymator is higher than that caused by the egg-larval endoparasitoid C. inanitus. The final body weight of a parasitised host larva by H. didymator and C. inanitus was only 6.7 and 13.0% of the maximum weight of an unparasitised sixth instar larva respectively. Moreover, parasitised larvae never reached the last instar. Results indicated that parasitised larvae might cause considerable less damage to the host plant than unparasitised ones.

Response of immunocompetent and immunosuppressed Spodoptera littoralis larvae to baculovirus infection

The Mediterranean lepidopteran pest Spodoptera littoralis is highly resistant to infection with the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) via the oral route, but highly sensitive to infection with budded virus (BV) via the intrahaemocoelic route. To study the fate of AcMNPV infection in S. littoralis, vHSGFP, an AcMNPV recombinant that expresses the reporter green fluorescent protein gene under the control of the Drosophila heat-shock promoter, and high-resolution fluorescence microscopy were utilized. S. littoralis fourth-instar larvae infected orally with vHSGFP showed melanization and encapsulation of virus-infected tracheoblast cells serving the midgut columnar cells. At 72 h post-infection, the viral foci were removed during the moult clearing the infection. Thus, oral infection was restricted by immune responses to the midgut and midgut-associated tracheal cells. By contrast, injection of BV into the haemocoel resulted in successful infection of tracheoblasts, followed by spread of the virus through the tracheal epidermis to other tissues. However, in contrast to fully permissive infections where tracheoblasts and haemocytes are equally susceptible to infection, a severe limitation to vHSGFP infection of haemocytes was observed. To investigate the resistance of S. littoralis haemocytes to BV infection with AcMNPV, the larval immune system was suppressed with the Chelonus inanitus polydnavirus or a putatively immunosuppressive polydnavirus gene, P-vank-1. Both treatments increased the susceptibility of S. littoralis larvae to AcMNPV. It is concluded that the resistance of S. littoralis to AcMNPV infection involves both humoral and cellular immune responses that act at the gut and haemocyte levels. The results also support the hypothesis that tracheolar cells mediate establishment of systemic baculovirus infections in lepidopteran larvae. The finding that polydnaviruses and their encoded genes synergize baculovirus infection also provides an approach to dissecting the responses of the lepidopteran immune system to viruses by using specific polydnavirus immunosuppressive genes.

Development of the anal vesicle, salivary glands and gut in the egg-larval parasitoid Chelonus inanitus: Tools to take up nutrients and to manipulate the host?

Larvae of endoparasitoids undergo extensive morphological changes and often have special features to allow their development inside the host. We present the first detailed study on the development of the anal vesicle and the gut. The analyses reveal that the anal vesicle is first seen on the dorsal side of the abdomen as an internal structure covered by a membrane. The morphology of the abdomen then changes intensively: new segments are formed and the anal vesicle develops from a crest of large cells to a protrusion. Towards the end of the first instar, the anal vesicle is fully evaginated and no longer covered by a membrane; the large epithelial cells have microvilli on their apical side which suggests uptake of nutrients from the host's haemolymph. When the larva has moulted to the second instar, the ultrastructure of the anal vesicle begins to change and shows signs of degeneration. In this stage the epithelium of the midgut is fully developed and has a brush border which suggests that nutrient uptake occurs now primarily through the midgut. The anal vesicle then degenerates completely. The salivary glands are prominent already in first instar larvae and appear to produce and release a host regulatory 212 kD protein.

Influence of the parasitoid Chelonus inanitus and its polydnavirus on host nutritional physiology and implications for parasitoid development

Chelonus inanitus is a solitary egg-larval endoparasitoid, which feeds on host haemolymph during its internal phase. Parasitization induces in the host Spodoptera littoralis a precocious onset of metamorphosis and a developmental arrest in the prepupal stage. At this stage the parasitoid larva emerges from the host and consumes it. We show here that parasitization and the co-injected polydnaviruses affect the nutritional physiology of the host mainly in the last larval instar. Polydnaviruses cause a reduced uptake of food and an increase in the concentration of free sugars in the haemolymph and of glycogen in whole body. The parasitoid larva, along with polydnaviruses, causes a reduction of proteins in the host's plasma and an accumulation of lipids in whole body. Dilution of host haemolymph led to a reduced concentration of lipid in parasitoid larvae and a reduced survival rate. Thus, a sufficient concentration of nutrients in the host's haemolymph appears to be crucial for successful parasitoid development. Altogether, the data show that the parasitoid and the polydnavirus differentially influence host nutritional physiology and that the accumulated lipids and glycogen are taken up by the parasitoid in its haematophagous stage as well as through the subsequent external host feeding.

Changes in the haemolymph proteome of Spodoptera littoralis induced by the parasitoid Chelonus inanitus or its polydnavirus and physiological implications

The egg–larval parasitoid Chelonus inanitus induces in its host Spodoptera littoralis two major developmental effects, namely a precocious onset of metamorphosis followed by a developmental arrest in the prepupal stage. Along with each egg, the wasp injects polydnavirus and venom into the host egg. The polydnavirus has been shown to play a major role in inducing the developmental arrest while the parasitoid larva is instrumental in inducing the precocious onset of metamorphosis. Here we report that experimental dilution of haemolymph of polydnavirus-containing larvae can partially prevent the developmental arrest while injection of native, but not of heat-treated, haemolymph or plasma from polydnavirus-containing larvae into nonparasitized larvae could induce developmental arrest in 14–15% of the larvae. This illustrates that heat-labile factors present in haemolymph play a role in causing developmental arrest. Injection of parasitoid medium increased the proportion of larvae entering metamorphosis precociously while injection of antibodies against a parasitoid-released protein had the opposite effect; this indicates that this protein and possibly other parasitoid-released substances are involved in inducing the precocious onset of metamorphosis. Analysis of the plasma proteome of nonparasitized, parasitized and polydnavirus-containing larvae revealed that the developmental effects are associated with only minor differences: eleven low abundant viral or virus-induced proteins and five parasitoid-released proteins were seen at specific stages of the host.

Cloning, characterization and analysis by RNA interference of various genes of the Chelonus inanitus polydnavirus

Successful parasitism of some endoparasitic wasps depends on an obligately symbiotic association with polydnaviruses. These unique viruses have a segmented genome consisting of circles of double-stranded (ds) DNA and do not replicate in the parasitized host. They are produced in the wasp's ovary and injected into the host along with the egg. Chelonus inanitus is an egg-larval parasitoid; its polydnavirus (CiV) has been shown to protect the parasitoid larva from the host's immune system and to induce developmental arrest in the prepupal stage. The genome of CiV consists of at least 10-12 segments and five have been sequenced up to now. Here, the complete (CiV12g2) or partial (CiV12g1, CiV16.8g1) cloning of three new CiV genes is reported. All three occur only on one viral segment and have no similarity to other known polydnavirus genes, with the exception of a high similarity of CiV12g1 to CiV14g1 and CiV12g2 to CiV14g2. Furthermore, the first attempt of in vivo application of RNA interference to study the function of polydnavirus genes is shown. Injection of dsRNA of two late- and one early- and late-expressed CiV genes into CiV/venom-containing host eggs partially rescued last-instar larvae from developmental arrest. Injection of the same dsRNAs into parasitized eggs partially reduced parasitoid survival, mainly by preventing the successful emergence of the parasitoid from the host. These viral genes thus seem to be involved in inducing developmental arrest and in keeping the cuticle soft, which appears to be necessary for parasitoid emergence and host feeding.