Diadromus Pulchellus Research Articles

Gustatory sensilla sensitive to protein kairomones trigger host acceptance by an endoparasitoid.

Proteins isolated from the host cocoon of Acrolepiopsis assectella (Lepidoptera: Yponomeutoidea) act as kairomones for host acceptance by the endoparasitoid wasp Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae). In this study, morphological, ultrastructural and electrophysiological studies were carried out in order to identify the contact chemoreceptive sensilla on the parasitoid antennae that perceive the protein kairomones. Three types of sensillum on the antennae of the females were found to have a chemosensory function. The receptor cell(s) of one sensillar type were shown to give a positive electrophysiological response to protein kairomones. This sensillar type is apically multiporous and female specific. Consequently, this sensillum could be the one implicated in the perception of the protein kairomone that triggers the host-acceptance behaviour of D. pulchellus females.

Effects of the Diadromus pulchellus ascovirus, DpAV-4, on the hemocytic encapsulation response and capsule melanization of the leek-moth pupa, Acrolepiopsis assectella

DpAV-4 is a symbiotic ascovirus found in natural populations of the solitary endoparasitoid wasp Diadromus pulchellus. The female wasp injects this virus into the pupae of the leek-moth Acrolepiopsis assectella during oviposition. The ascovirus replicates in the pupal tissues and the consequent lysis of the cells occurs synchronously with egg hatching and the development of the wasp larva. We show here that encapsulation and capsule melanization were activated when minute nylon monofilaments were implanted into the hemocoel of non parasitized leek-moth pupae and that encapsulation and melanization were inhibited in pupae parasitized by D. pulchellus. When the pupae were infected by DpAV-4, melanization of the nylon monofilaments was abolished, but a capsule was still always formed. These results indicate that DpAV-4 is a free virus able to alter the defence system of the parasitized host so as to improve the development of the parasitoid wasp, D. pulchellus.

Frequency and viability of diploid and haploid male offspring of mated females of solitary endoparasitoid Diadromus pulchellus

Sex determination in the order Hymenoptera is based on arrhenotoky, hymenopteran males are usually haploid and females diploid. Males of the Ichneumonidae Diadromus pulchellus, solitary endoparasitoid of A Acrolepiopsis assectella pupae, are normally haploid, but diploid males are present in a natural population and can be obtained in an experimental population. The future of an ovocyte laid by mated females of the solitary endoparasitoid D. pulchellus was characterised by six probabilities related to the sex and development of the ovocyte. The probabilities of fertilisation of female ovocyte ( k 1) or non-fertilisation ( k 3) showed that an inseminated female functioned as a unmated female for half of the time (since k 1 = 0.492 and k 3 = 0.455) with the probability of fertilisation of male ovocyte, k 2, equal to 0.053.The survival probabilities of each type of ovocyte showed that an ovocyte had a high probability of developing up to the adult stage, although the difference between the calculated sex ratios at laying (males/females = 1.032) and at emergence (0.90) revealed a slight reduction in the number of haploid sons. The probabilities of fertilisation and of viability of all the ovocytes laid by each of the 33 mated females were analysed by an ascending hierarchical classification of Euclidean distances and by an analysis of their principal components. The 33 mothers were distributed into four distinct sub-groups characterised by a sex ratio varying from an exclusive presence of females to an exclusive presence of males. Our hypothesis was that this distribution in four sub-sets could not simply result from the random nature of the sample.

Phylogenetic position of the Diadromus pulchellus ascovirus DNA polymerase among viruses with large double-stranded DNA genomes

The ASCOVIRIDAE: is a family of large double-stranded (ds) DNA insect viruses that contains four species, the Spodoptera frugiperda (SfAV1), Trichoplusia ni (TnAV2), Heliothis virescens (HvAV3) and Diadromus pulchellus (DpAV4) ascoviruses. These are unique among insect viruses in that the primary means of transmission among their lepidopteran hosts is generally by being vectored mechanically by hymenopteran parasitoids. Ascoviruses are similar in virion structure, but their relationships with their parasitoid vectors vary from being opportunistic to obligate. Little is known, however, about the relatedness of these viruses to one another or to other large dsDNA viruses. We therefore cloned and sequenced the delta DNA polymerase gene of DpAV4, characterized it and compared it to 59 eukaryotic and viral delta and epsilon DNA polymerases. Phylogenetic analyses based on these genes revealed that the ascoviruses DpAV4 and SfAV1 formed a group of virus species distinct from, but closely related to, species of the family IRIDOVIRIDAE: Detailed analyses of the relatedness of ascovirus species based on conserved delta DNA polymerase motifs showed two groups within the family ASCOVIRIDAE:, one containing DpAV4 and the other containing SfAV1, TnAV2 and HvAV3, which was consistent with their host-vector relationships. Despite significant differences in capsid symmetry between ascoviruses and iridoviruses, these results suggest that these viruses may have originated from a common ancestral virus.

Characterization of repetitive DNA regions and methylated DNA in ascovirus genomes.

The accompanying phylogenetic study of large double-stranded DNA viruses based on their delta DNA polymerase genes suggests that ascoviruses (family ASCOVIRIDAE:) and iridoviruses (family IRIDOVIRIDAE:) are closely related and may share a common ancestor. This relationship was unexpected because of marked differences between these viruses. Iridoviruses produce icosahedral virions and occur broadly among vertebrates and invertebrates, whereas ascoviruses typically produce reniform or bacilliform virions and are restricted to insect hosts, primarily lepidopterans. Detailed comparisons of these two virus types are not possible because fundamental information on the properties of the virions and their genomes is lacking, especially for ascoviruses. To facilitate further investigation of the putative evolutionary relationship between ascoviruses and iridoviruses, the genomes of representative viruses from each family were compared with respect to physical configuration, presence of DNA repeats and degree of DNA methylation. Genomes from Spodoptera frugiperda (SfAV1), Heliothis virescens (HvAV3) and Diadromus pulchellus (DpAV4) ascoviruses were all found to be circular and partially superhelical and to contain large interspersed repeats of 1-3 kbp. Mosquito (IV type 3), lepidopteran (IV type 6) and isopod (IV type 31) iridovirus genomes were all linear and lacked large regions of repetitive DNA. Ascovirus and iridovirus genomes were methylated and one, DpAV4, had the highest degree of methylation of any reported animal DNA virus. The major differences in the physical and biochemical characteristics of ascoviruses and iridoviruses reported here provide a foundation for further studies of their relatedness while making their possible close relationship and divergence during evolution of even greater interest.

Effects of sulfur-containing precursors of Allium secondary metabolites on behavior and physiology of Diadromus pulchellus, a specialist parasitoid of Acrolepiopsis assectella

Diadromus pulchellus, a monophagous parasitoid of the leek moth, Acrolepiopsis assectella, a specialist of plants in the Allium genus, was raised on four series of chrysalids coming from four diets: leek leaves (LL), an artificial diet with (D + L) or without (D − L) leek powder, and an artificial diet plus 1% methyl-cysteinesulfoxide, a precursor of characteristic sulfur volatiles (D + P). Various behavioral and physiological responses by the parent parasitoids and the progeny were studied. No differences were observed in behavior among the four series. The higher precursor concentration observed in LL and in D + P than in D + L and D − L was responsible for a lower emergence ratio and higher egg production in LL and D + P. The consequences of these variations are discussed in relation to narrowness of the tritrophic system. The fact that sulfur volatiles favorable to behavior arise from nonvolatile sulfur precursors, having negative effects on physiology, can also contribute to the maintenance of the system.

Free serosal cells originating from the embryo of the wasp Diadromus pulchellus in the pupal body of parasitized leek-moth, Acrolepiosis assectella. Are these cells teratocyte-like?

In braconid species, teratocytes are derived from a serosal cell membrane which envelops the developing parasitoid embryo. On hatching, this membrane dissociates into individual cells, the teratocytes, which then circulate in the haemolymph of the host. We describe herein such a membrane, surrounding the embryo in eggs of the ichneumonid parasitoid wasp, Diadromus pulchellus. This membrane consisted of a single sheet of tightly packed cells with large 12±1.4 μm nuclei. These cells were released after hatching in vitro and cells of the same size were detected in vivo, in the vicinity of the D. pulchellus embryo. The number of nuclei detected suggests that the serosal membrane consists of about 450±150 cells. These cells did not grow after hatching of the parasitoid egg in the parasitized host, Acrolepiosis assectella, during the development of the parasitoid wasp larva. Southern blot experiments, using D. pulchellus satellite DNA or the ribosomal genes as probes, showed that free-living floating cells of wasp origin were present in the body of the parasitized host. This is the first time that free-floating teratocyte-like cells have been described in species of the Ichneumonidae.

Polypeptides of Acrolepiopsis assectella cocoon (Lepidoptera: Yponomeutoidea): an external host-acceptance kairomone for the parasitoid Diadromus pulchellus (Hymenoptera: Ichneumonidae)

Contact kairomones are essential for host-acceptance behaviour by female parasitoids. In the solitary endoparasitoid wasp, Diadromus pulchellus, this behaviour depends mainly on compound(s) in the cocoon of their host, Acrolepiopsis assectella pupae. Extracts of empty cocoons and polypeptides extracted from cocoons were tested in acceptance behaviour assays using cotton fibre lures bearing extracts. Extractions with solvents of increasing polarity indicated that the active compounds were polar, while SDS–PAGE showed that four glycopolypeptides contained enough information to trigger host-acceptance behaviour in female wasps. This kairomonal activity was found to be due to the protein moieties, and was independent of any glycosylation. These four glycopolypeptides might be two variants of two soluble sericin-like polypeptides differing in their degree of glycosylation.

Satellite DNA transcription in Diadromus pulchellus (Hymenoptera)

Previous studies have shown that the satellite DNAs in Hymenoptera account for 1–25% of the genome. They mainly correspond to a single family, or to several subfamilies having the same evolutionary origin. We have now showed that the satellite DNAs in the genomes of the hymenopterans Diadromus pulchellus, Diadromus collaris, Eupelmus vuilletti and Eupelmus orientalis are transcribed in both males and females. Satellite DNA transcripts could only be extracted with NP40/Urea, indicating that they are strongly associated with proteins. The satellite DNA in D. pulchellus was transcribed on the two DNA strands. The satellite DNA transcripts were single-stranded and not polyadenylated in vivo. The transcripts were found in embryos, larvae and imagos stages. The transcripts detected included one major transcript (1.9 kb) and several discrete smaller transcripts. The in vivo synthesis of these satellite DNA transcripts was explored by identifying their putative initiation sites.

Biological and molecular features of the relationships between Diadromus pulchellus ascovirus, a parasitoid hymenopteran wasp (Diadromus pulchellus) and its lepidopteran host, Acrolepiopsis assectella.

The Diadromus pulchellus ascovirus (DpAV) has been isolated from laboratory strains of Diadromus pulchellus and in natural wild populations collected from the Antibes locality (southern France). The DpAV genome was found in the cells of the head, thorax and abdomen of this hymenopteran wasp. DpAV virions are present in the female genitalia and are transmitted to the nymphal lepidopteran host, Acrolepiopsis assectella, at each oviposition of the female wasp. The presence of the DpAV genome in all Diadromus somatic cells suggests that it is inherited by vertical transmission. DpAV is amplified in the host tissues during the larval development of D. pulchellus in A. assectella. Cell lysis due to amplification of the virus does not prevent the development of the hymenopteran larva. Virus amplification appears to be slower in nymphs parasitized by D. pulchellus than in nymphs artificially infected with DpAV alone. Lysis of the nymphal cells due to viral replication seems to be synchronous with egg hatching and the development of the hymenopteran larva. The features of DpAV and its relationship with the parasitoid wasp D. pulchellus during its development are compared to those of the ichnoviruses.

Particle and genomic characteristics of a new member of the Ascoviridae: Diadromus pulchellus ascovirus.

A new member of the family Ascoviridae, Diadromus pulchellus ascovirus (DpAV), has been found in the lepidopteran nymphs of Acrolepiopsis assectella parasitized by the hymenopteran wasp Diadromus pulchellus. Virions have the standard features of the ascovirus group; each particle is about 220 nm long and 150 nm wide. They are multilayered, with two clear 7-nm-thick outer layers and one 15-nm-thick inner layer surrounding an electron-dense core (155 x 110 nm). However, the flattened rice-grain shape and fragility of the DpAV particles are unlike that of known ascoviruses infecting Noctuidae species. They form large vesicles containing virions in infected cells. The DpAV genome is about 116 kb long and has a circular and relaxed structure. It contains 6-8 repeated and interspersed sequences of 494 bp. The structural and genomic features of DpAV suggest that this virus belongs to an ascovirus sub-family different from that containing the ascoviruses previously found to infect species of Noctuidae (Federici et al., 1991).

Origin and identification of bacteria which produce kairomones in the frass of Acrolepiopsis assectella (Lep., Hyponomeutoidea).

The volatiles used by the parasitoid Diadromus pulchellus to find its host, the leek moth, are produced by the bacteria developing in the frass of the host larvae. The origin and the nature of these bacteria were investigated. Samples were taken from healthy leeks and from infested leeks in the field, as well as from the frass of larvae reared in the laboratory either on the host plant or on an artificial diet. The various species of bacteria identified were cultured in the presence of precursors of leek sulphur volatiles and their volatile emissions were analysed. Klebsiella oxytoca and various Bacillus, common decomposers of plant matter, were the principal species producing active volatiles which were alkyl disulphides.

Precedence of the first male sperm in successive matings in the Hymenoptera Diadromus pulchellus

AbstractIn most insect species where double matings occur, sperm from the second male preferentially fertilize subsequent eggs. However, we demonstrate here that, as already shown for some other hymenopteran species, this is not the case in the ichneumonid wasp Diadromus pulchellus (Wesmeal): sperm from the first male usually father all the female progeny. This precedence of the first male sperm is also observed in double matings involving an haploid male and a diploid sterile male, whichever is the first mating male. We discuss the consequences of this phenomenon from an evolutionary point of view.

The Genome Segments of DpRV, a Commensal Reovirus of the Wasp Diadromus pulchellus (Hymenoptera)

The complete nucleotide sequences of five double-stranded RNA genome segments of the Diadromus pulchellus reovirus (DpRV) have been determined. They consist of 985, 1240, 1318, 1652, and 4230 bp. Each segment contains at least one putative open reading frame encoding 33-, 40-, 45-, 49-, and 148-kDa proteins, respectively. The proteins have no significant similarities with sequences in data banks. Analysis of these segments and of two other previously published segments revealed the presence of degenerate consensus inverted repeats at both ends (5′-rCAAUUUUnnACU...AGUAAAAAAAUnrG3′). The biological, structural, and genomic features of DpRV suggest that this virus is related to members of the Orthoreovirus genus.

A Member of the Reoviridae (DpRV) Has a Ploidy-Specific Genomic Segment in the Wasp Diadromus pulchellus (Hymenoptera)

Wild and laboratory populations of the parasitoid wasp Diadromus pulchellus are infected with a new member of the reoviridae (DpRV) described in this paper. The particles of this virus possess two capsid shells (diameters: 35 and 70 nm) made up of 11 proteins. The virus is present mainly in the gut of the wasp, with smaller quantities in its venom gland. The genome of virus particles purified from haploid insects (functional males) contains 10 segments, whereas virus from diploid insects (females and sterile diploid males) contains a supernumerary 3.33-kb segment. The sequence of this dsRNA segment revealed that it is a triplicated 1050-bp motif which is 97.5% similar to the 5′ region of one of the 10 basic segments, the 3.80-kb segment.

Microorganisms are involved in the production of volatile kairomones affecting the host seeking behaviour of Diadromus pulchellus, a parasitoid of Acrolepiopsis assectella

Abstract. Experiments were carried out to determine the origin of dialkyl disulphides found in the larval frass of Acrolepiopsis assectella Zell. which enable the specialist parasitoid Diadromus pulchellus Wsm. to find its host. These kairomones are not specific: they are also found in the frass of the generalist Cacoecimorpha pronubana Hb. fed a leek‐based diet. They are emitted only after the frass emerges from the gut. Bacteria are present in the gut of larvae and in their frass. The addition of antibiotics to the larval diet prevents bacterial development and suppresses disulphide emission. When grown in the presence of sulphur amino acids, precursors of sulphur volatiles, some bacteria metabolize kairomones. The production of volatile kairomones, responsible for host– parasitoid relationships, depends on the presence of additional organisms, i.e. bacteria, and not on enzymes arising from the plant or the phytophage.

Sex determination in the hymenopteran Diadromus pulchellus (Ichneumonidae): validation of the one-locus multi-allele model

Males of the hymenopteran Diadromus pulchellus are normally haploid, but diploid males can be obtained by inbreeding. Inbred crosses within strains that are polymorphic at the enzymatic loci Pgm-2 and Ao-4 or that differ by a body colour mutation produce heterozygous diploid males in offspring. The genotypic distributions observed in such progeny were compared with expected results under the one-locus sex determination model or the two independent loci model. The results show that only the one-locus multi-allele model fits the data and allow a provisional estimate of ∼ 15 sex alleles. These conclusions generalize the case of existence of a single locus to determine sex in Hymenoptera and are discussed at the evolutionary level.

The 28S ribosomal RNA-encoding gene of Hymenoptera: inserted sequences in the retrotransposon-rich regions

The genomes of two parasitoid wasps, Diadromus pulchellus and Eupelmus vuilleti, and the honey bee, Apis mellifera, contain few interspersed repeated sequences corresponding to transposons (Tn). This suggests that the genomic organisation of Hymenoptera could be due to the elimination of deleterious Tn in haploid males. We have used restriction-fragment length polymorphism analysis to show that nondeleterious Tn are present in the DNA (rDNA) encoding ribosomal RNA of twelve species of Hymenoptera. Sequence analysis of the 28S rDNA type-I and type-II insertion-rich regions of 80 species showed that this region is very highly conserved (95.8%). A consensus sequence and restriction map of the rDNA region were established. These sequence data were used to develop a strategy for detecting inserted elements in the rDNA fragments containing type-I or type-II insertion sites, and this strategy was used to screen twelve hymenopteran species and four non-Hymenoptera control species. The rDNA fragments from the Hymenoptera and control species contained inserted sequences in the area where type-I and type-II elements are inserted in the 28S rDNA retrotransposon-rich region of Diptera and Lepidoptera. The hymenopteran genomes therefore appear to contain repeated elements, the mobility and nature of which remain to be determined.

Host selection behavior of Campoletis sonorensis: A model system

Plants play a role in the host selection strategy of Campoletis sonorensis , an ichneumonid parasitoid that attacks the larval stages of a number of plant-feeding lepidoptera. We examine the early host selection behavior of C. sonorensis in response to plants and the herbivores that serve as hosts. We bring together some new data and organize the published information to provide an overview of the host selection behavior of Campoletis . We also compare the results of our studies utilizing C. sonorensis , a generalist, to published data concerning two specialists, Microplitis croceipes , a braconid with the same host system, and Diadromus pulchellus , an ichneumonid specializing in both the plant and the hosts it attacks.

Molecular analysis of the genomic organization of the Hymenoptera Diadromus pulchellus and Eupelmus vuilleti

AbstractThe genomic organization of two parasitic wasps was analyzed by DNA reassociation. Cot curves revealed a pattern with three types of components. A highly repetitive DNA, accounting for 15 to 25% of the genome, was identified as satellite DNA. The moderately repetitive DNA corresponds to 26 to 42% of the genome in both species, and shows large variations in complexity, repetitive frequency and a number of sub‐components between males and females. These variations are seen as resulting from DNA amplification during somatic and sexual differentiation. Dot blot analyses show that such DNA amplifications concern several types of structural and regulatory genes. The presence of repeated mobile elements was studied by the Roninson method to compare the repeated sequence patterns of Diadromus pulchellus and Eupelmus vuilleti with those of Drosophila melanogaster. The occurrence and organization of mobile elements in these Hymenoptera differ from those of the neighboring order of Diptera. The repetitive and unique components define very large genomes (1 to 3 × 109 base pairs). The genomic organization in Parasitica appears to be an extreme drosophilan type. We propose that the germinal genome of these parasitic wasps is primarily composed of satellite DNA blocks and very long stretches of unique sequences, separated by a few repeated and/or variously deleted, interspersed elements of each mobile element family.