Wasp Host Research Articles

Seasonal incidence of two co-occurring adult parasitoids of Acalymma vittatum in New York State: Centistes (Syrrhizus) diabroticae and Celatoria setosa

We report the incidence of striped cucumber beetle (Acalymma vittatum [Fabricius]) (Coleoptera: Chrysomelidae) parasitism in bi-weekly samples from diverse farm locations in central New York State over the course of two growing seasons. Two parasitoid species not previously verified in this geographic region were found: Celatoria setosa (Coquillett) (Diptera: Tachinidae) and Centistes (Syrrhizus) diabroticae (Gahan) (Hymenoptera: Braconidae). Parasitism by C. setosa, up to 43%, [mean 8.67%] was comparable to previously published rates. Contrary to the expectations of earlier authors, however, C. diabroticae was found to be ubiquitous and maximum rates of parasitism (~54%) were >threefold greater than the only other published report for this species [C. diabroticae mean 14.36%]. In laboratory assays, we investigated C. diabroticae larval development. We also tested the effects of wasp clone and host beetle sex on C. diabroticae larval development. This is the first documentation of life cycle information for this braconid.

Essential but unhelpful wasp Wolbachia

Essential but unhelpful wasp Wolbachia

Schistonchus virens sp. n. (Aphelenchoididae) and Parasitodiplogaster australis sp. n. (Diplogastridae) from Ficus virens (Moraceae) in Australia

Abstract A new species each of Schistonchus and Parasitodiplogaster were recovered from the sycones of Ficus virens from St Lucia, Brisbane, QLD, Australia. This is also the first record of Parasitodiplogaster from Australia. The species are described here as Schistonchus virens sp. n. and Parasitodiplogaster australis sp. n. Schistonchus virens sp. n. is differentiated from other species of the genus by a combination of morphological characters, including C-shaped females and males, excretory pore opening located near the head, a short post-vulval uterine sac, rose-thorn-shaped spicule, amoeboid sperm, no gubernaculum, three pairs of subventral papillae on the male tail, DNA sequence data; biogeographical range and host wasp and Ficus species affiliation. Parasitodiplogaster australis sp. n. is differentiated from all other species of the genus by having females with only one gonad, males with C-shaped spicules with an arcuate, slender gubernaculum, characteristic arrangement of the male caudal papillae and DNA sequence data. The generic diagnosis of Parasitodiplogaster is emended to include loss of a female gonad.

A Technique of Segment Expression and RNA Interference (SERI) Reveals a Specific Physiological Function of a Cysteine-rich Protein Gene Encoded in Cotesia plutellae Bracovirus

As a provirus, polydnavirus has a segmented DNA genome on chromosome(s) of host wasp. It contains several genes in each segment that presumably play critical roles in regulating physiological processes of target insect parasitized by the wasp. A cysteine-rich protein 1 (CRP1) is present in the polydnavirus Cotesia plutellae bracovirus (CpBV) genome, but its expression and physiological function in Plutella xylostella parasitized by the viral host C. plutellae is not known. This CpBV-CRP1 encoding 189 amino acids with a putative signal peptide (20 residues) was persistently expressed in parasitized P. xylostella with gradual decrease at the late parasitization period. Expression of CpBV-CRP1 was tissue-specific in the fat body/epidermis and hemocyte, but not in the gut. Its physiological function was analyzed by inducing transient expression of a CpBV segment containing CpBV-CRP1 and its promoter, which caused significant reduction in hemocyte -spreading and delayed larval development. When the treated larvae were co-injected with double-stranded RNA of CpBV-CRP1, the expression of CpBV-CRP1 disappeared,whereas other genes encoded in the CpBV segment was expressed. These co-injected larvae significantly recovered the hemocyte-spreading capacity and larval development rate. This study reports that CpBV-CRP1 is expressed in P.xylostella parasitized by C.plutellae and its physiological function is to alter the host immune and developmental processes.

A simple technique for the preliminary screening of parasitic wasps for polydnavirus-like particles

Certain hymenopteran parasitoid species in the families Ichneumonidae and Braconidae contain symbiotic viruses known as polydnaviruses (PDVs; Polydnaviridae) (Stoltz et al. 1984; Beckage 1998; Pennacchio & Strand 2006). PDVs have double-stranded DNA (dsDNA) genomes that are segmented, with up to 30 circular dsDNAs reported (Espagne et al. 2004; Kroemer & Webb 2004; Pennacchio & Strand 2006). The PDVs of both ichneumonids (ichnoviruses) and braconids (bracoviruses) occur as proviruses integrated in the wasp genome, with replication and virus particle production occurring only in the wasp ovaries in a region called the calyx (Fleming 1992; Albrecht et al. 1994; Strand & Pech 1995). A very high number of virus particles (containing circular episomal forms of the integrated DNA genome) are released (by cell rupture in braconids) or secreted (by ichneumonids) from the calyx cells into the oviducts and during oviposition the PDVs are injected with the eggs and ovarian fluid into the host larvae (Stoltz & Vinson 1979; Fleming 1992; Dupuy et al. 2006). Although there is no PDV replication in the wasp's host, PDV gene expression in the host disrupts the host's development and cellular defence systems thus allowing the wasp's progeny to survive and complete their development (Strand & Pech 1995; Webb 1998; Pennacchio & Strand 2006; Webb et al. 2006).

Extreme diversity of tropical parasitoid wasps exposed by iterative integration of natural history, DNA barcoding, morphology, and collections

We DNA barcoded 2,597 parasitoid wasps belonging to 6 microgastrine braconid genera reared from parapatric tropical dry forest, cloud forest, and rain forest in Area de Conservación Guanacaste (ACG) in northwestern Costa Rica and combined these data with records of caterpillar hosts and morphological analyses. We asked whether barcoding and morphology discover the same provisional species and whether the biological entities revealed by our analysis are congruent with wasp host specificity. Morphological analysis revealed 171 provisional species, but barcoding exposed an additional 142 provisional species; 95% of the total is likely to be undescribed. These 313 provisional species are extraordinarily host specific; more than 90% attack only 1 or 2 species of caterpillars out of more than 3,500 species sampled. The most extreme case of overlooked diversity is the morphospecies Apanteles leucostigmus. This minute black wasp with a distinctive white wing stigma was thought to parasitize 32 species of ACG hesperiid caterpillars, but barcoding revealed 36 provisional species, each attacking one or a very few closely related species of caterpillars. When host records and/or within-ACG distributions suggested that DNA barcoding had missed a species-pair, or when provisional species were separated only by slight differences in their barcodes, we examined nuclear sequences to test hypotheses of presumptive species boundaries and to further probe host specificity. Our iterative process of combining morphological analysis, ecology, and DNA barcoding and reiteratively using specimens maintained in permanent collections has resulted in a much more fine-scaled understanding of parasitoid diversity and host specificity than any one of these elements could have produced on its own.

Parasitic mites as part-time bodyguards of a host wasp

Some bees and wasps that host mites have peculiar pocket-like structures called acarinaria. These have long been considered as morphological adaptations to securely transfer beneficial mites into nests, and thus are thought to be the product of a mutualistic relationship. However, there has been little compelling evidence to support this hypothesis. We demonstrated that the parasitic mite Ensliniella parasitica, which uses acarinaria, increases the reproductive success of its host wasp Allodynerus delphinalis by protecting it from parasitoid wasps. Every time the parasitoid Melittobia acasta accessed a prepupal or pupal wasp host cell, adult mites attacked it, continuously clinging to it and possibly piercing the intersegmental membrane of the parasitoid with their chelicerae. Subsequent mortality of the parasitoid depended on the number of attacking mites: an average of six mites led to a 70% chance of mortality, and 10 mites led to a 100% chance of mortality. In this way, parent mites protect the food source (juvenile wasps) for themselves and ultimately for their offspring. We propose that wasps evolved acarinaria to maintain this protective guarding behaviour.

ONE FIG TO BIND THEM ALL: HOST CONSERVATISM IN A FIG WASP COMMUNITY UNRAVELED BY COSPECIATION ANALYSES AMONG POLLINATING AND NONPOLLINATING FIG WASPS

The study of chalcid wasps that live within syconia of fig trees (Moraceae, Ficus), provides a unique opportunity to investigate the evolution of specialized communities of insects. By conducting cospeciation analyses between figs of section Galoglychia and some of their associated fig wasps, we show that, although host switches and duplication have evidently played a role in the construction of the current associations, the global picture is one of significant cospeciation throughout the evolution of these communities. Contrary to common belief, nonpollinating wasps are at least as constrained as pollinators by their host association in their diversification in this section. By adapting a randomization test in a supertree context, we further confirm that wasp phylogenies are significantly congruent with each other, and build a "wasp community" supertree that retrieves Galoglychia taxonomic subdivisions. Altogether, these results probably reflect wasp host specialization but also, to some extent, they might indicate that niche saturation within the fig prevents recurrent intrahost speciation and host switching. Finally, a comparison of ITS2 sequence divergence of cospeciating pairs of wasps suggests that the diversification of some pollinating and nonpollinating wasps of Galoglychia figs has been synchronous but that pollinating wasps exhibit a higher rate of molecular evolution.

Life cycle and sexual mode adaptations of the parasitic mite Ensliniella parasitica (Acari: Winterschmidtiidae) to its host, the eumenine wasp Allodynerus delphinalis (Hymenoptera: Vespidae)

We investigated two important life-history traits in parasites, i.e., life cycle and reproductive mode, that should be adapted to specific hosts using the parasitic mite Ensliniella parasitica Vitzthum, 1925 and the host wasp Allodynerus delphinalis (Giraud, 1866) in field- and laboratory-reared nests. The life cycle of E. parasitica was synchronized with that of the wasp; this synchronization facilitated dispersal. Life-cycle plasticity of the mite was low and development was halted on dead hosts. There was no significant difference in wasp juvenile mortality between mite-laden and mite-free individuals under controlled conditions. Therefore, the mites were suggested to be not toxic to the hosts. We confirmed for the first time that virgin female mites ovoviviparously produce arrhenotokous males the size of a protonymph to compensate for the absence of males in a cell. Although no obvious antagonistic behaviour between large (i.e., sexual) and small males was observed, large males mounted females on late prepupal hosts, about 1–2 days before either the egg or the small male was laid. We conclude that the adaptations of the mite to its host involve life-cycle synchronization, low-impact parasitism, and facultative parthenogenesis.

Exploitation of cytoplasmic and nuclear actin by baculoviruses

Diverse bacterial and viral pathogens hijack the actin cytoskeleton of host cells to facilitate processes such as attachment, internalization, or spread. Among known pathogens, baculoviruses are unique in their ability to manipulate actin both in the cell cytoplasm and nucleus. We seek to determine how baculoviruses exploit actin to reveal new roles for actin in pathogenesis, and to illuminate the poorly understood function and regulation of nuclear actin. Using time‐lapse microscopy, we find that Autographa californica Multiple Nucleopolyhedrovirus (AcMNPV) undergoes actin‐based motility within the cell cytoplasm. Motility requires p78/83, a viral capsid protein that mimics host WASP proteins and activates actin assembly with the host Arp2/3 complex. As with other pathogens, moving AcMNPV are propelled into surface projections that may function in cell‐to‐cell spread. However, unlike other pathogens, motility also enhances viral collision with the nucleus, enabling translocation into the nucleus, where replication takes place. Once in the nucleus, AcMNPV induces nuclear actin accumulation, and then assembles nuclear actin using p78/83 to activate the host Arp2/3 complex. Nuclear actin assembly by p78/83 and Arp2/3 complex is essential for progeny production. Further study of this novel mode of pathogenesis will likely reveal elusive details about the regulation and function of nuclear actin.

Differential expression profile of genes encoded in a genome segment of Cotesia plutellae bracovirus in a parasitized host, Plutella xylostella

AbstractThe Polydnaviruses are an insect DNA virus group. The segmented genome of a polydnavirus is located on the host wasp chromosome as a provirus. After replication, virions are delivered into the parasitized host, where their expression products play significant roles in specific processes of parasitism. However, little is known about how viral gene expression is controlled. In the present study, we tested whether different genes in a genome segment are expressed concomitantly. Cotesia plutellae bracovirus (CpBV) is a polydnavirus mutualistic to an endoparasitoid, Cotesia plutellae (Braconidae: Hymenoptera). Its circular genome segments in viral particles were captured by a transposon containing pUC origin sequence and replicated in Escherichia coli. CpBV‐S30 (23.5 kb), one of the large CpBV genome segments, was fully sequenced, and seven open reading frames (ORF) were predicted. We analyzed expression patterns of the seven ORF in the diamondback moth, Plutella xylostella, parasitized by C. plutellae. Transcription analyses indicated that all ORF of CpBV‐S30 in the parasitized P. xylostella were expressed from the first day of parasitization and then expression levels decreased over the period of parasitization, except for CpBV‐H4, which showed an additional expression peak. In terms of tissue specificity in their expression patterns, all ORF were found to be expressed in the fat body, hemocytes and gut of the parasitized host. Promoter sequence analysis showed that all seven ORF had typical promoter elements, including TATA binding sites, but promoter component numbers and kinds varied. These results suggest that genes in a genome segment of CpBV can differentially express in the parasitized host, presumably by their different promoter components.

Olfactory conditioning in mate searching by the parasitoidAphidius ervi(Hymenoptera: Braconidae)

Despite the fact that insect learning capacity has been broadly demonstrated, the role that this process plays during mate searching has been scarcely explored. We studied whether the sexual behaviour of a male parasitic wasp can be conditioned to the odours from two alternative host plant complexes (HPCs) present during its first copulation. The experimental subjects were newly emerged males of the aphid parasitoid, Aphidius ervi, and two alternative HPCs (alfalfa or wheat). In the training protocol, copulation experience corresponded to an unconditioning stimulus and HPC odours to the conditioning stimuli. The initial (just after eclosion) and trained responses were assessed in a glass Y-olfactometer. The results showed that neither alfalfa HPC nor wheat HPC stimuli elicited sexual-related behaviours in initial male responses. Conversely, both HPCs triggered strong attraction and wing fanning courtship behaviour in trained responses when the male was exposed to a female plus HPC during training. In males trained with females plus a given HPC but tested with the alternative HPC in the olfactometer, trained response showed a similar trend to the non-associative treatments. Hence, through learning, the olfactory stimulus context present during copulation could become a predictive cue for further mate searching. These results are discussed in terms of parasitic wasp ecology and host fidelity.

Interspecific competition between the ichneumonid Campoletis chlorideae and the braconid Microplitis mediator in their host Helicoverpa armigera

AbstractWe investigated interspecific competition between Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) and Microplitis mediator (Haliday) (Hymenoptera: Braconidae) in their host, the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) under laboratory conditions. Cotton bollworm larvae were allowed to be parasitized by both wasp species simultaneously or sequentially at different time intervals. When host larvae were parasitized simultaneously by both parasitoids, the majority of the cocoons produced were of M. mediator. When host larvae were parasitized initially by M. mediator followed by C. chlorideae at 12 or 24 h, parasitoids emerging from the multiparasitized hosts were mainly M. mediator. In contrast, when host larvae were parasitized initially by C. chlorideae, followed by M. mediator 12 or 24 h later, parasitoids emerging from the multiparasitized hosts were mainly C. chlorideae. Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that first instars of M. mediator could physically attack the larvae of C. chlorideae, but not the eggs of C. chlorideae. When a host was parasitized by both wasp species sequentially, more host larvae died and the number of wasp offspring was significantly reduced compared to a host parasitized by only one wasp. Conversely, in simultaneous multiparasitism, the host mortality and wasp offspring production were not significantly different from those parasitized by single wasp species.

An Evidence for Host Translation Inhibitory Factor Encoded in a Polydnavirus, Cotesia glomerata Bracovirus, Genome and Its Expression in Parasitized Cabbage White Butterfly, Pieris rapae

Polydnavirus is a DNA virus symbiotic to some endoparasitic wasps and plays a critical role in accomplishing successful parasitic life cycle of host wasps. Host translation inhibitory factor (HTIF) has been found in some polydnaviral genomes and performs parasitic functions leading to host immunosuppression and redirecting host nutrient usage to wasp development. The cabbage white butterfly, Pieris rapae, parasitized by a gregarious endoparasitoid, Cotesia glomerata, undergoes several physiological alterations including immune malfunctioning and failure of pupal metamorphosis. C. glomerata possesses its own symbiotic polydnavirus, C. glomerata bracovirus (CgBV). Its genome consisted of at least 12 segments in unequal amounts. Parasitized P. rapae hemolymph contained HTIF-like protein, which was determined through an immunoblotting assay using HTIF antibody of C. plutellae bracovirus (CpBV). RT-PCR using HTIF primers of CpBV produced an HTIF-like gene in P. rapae larvae parasitized by C. glomerata. Also, this HTIF-like gene was encoded in CgBV genome and its partial sequence of CgBV showed highly homology (98.5%) to amino acid sequence of an HTIF of CpBV, called CpBV15a. These results suggest that a common HTIF-like moiety may be shared among Cotesia-associated bracovirus.

Habitat modification alters the structure of tropical host–parasitoid food webs

Global conversion of natural habitats to agriculture has led to marked changes in species diversity and composition. However, it is less clear how habitat modification affects interactions among species. Networks of feeding interactions (food webs) describe the underlying structure of ecological communities, and might be crucially linked to their stability and function. Here, we analyse 48 quantitative food webs for cavity-nesting bees, wasps and their parasitoids across five tropical habitat types. We found marked changes in food-web structure across the modification gradient, despite little variation in species richness. The evenness of interaction frequencies declined with habitat modification, with most energy flowing along one or a few pathways in intensively managed agricultural habitats. In modified habitats there was a higher ratio of parasitoid to host species and increased parasitism rates, with implications for the important ecosystem services, such as pollination and biological control, that are performed by host bees and wasps. The most abundant parasitoid species was more specialized in modified habitats, with reduced attack rates on alternative hosts. Conventional community descriptors failed to discriminate adequately among habitats, indicating that perturbation of the structure and function of ecological communities might be overlooked in studies that do not document and quantify species interactions. Altered interaction structure therefore represents an insidious and functionally important hidden effect of habitat modification by humans.

Pattern of gene duplication in the Cotesia congregata Bracovirus

Polydnaviruses (PDVs) are a family of double-stranded DNA viruses genetically linked to their wasp hosts. These viruses utilize the transcriptional machinery of the wasp cells to manufacture viral particles which contain circular segments of DNA. The female wasp, hosting the polydnavirus, lays its eggs along with the viral particles inside a caterpillar. Because no replication of the virus occurs while inside the caterpillar, fixed genetic changes occur solely inside the female wasp, as an integrated portion of its genome. Therefore, evolution of the polydnavirus is expected to parallel that of the wasp. Phylogenetic analysis of the polydnavirus genome showed a pattern of gene duplication consistent with the “birth-and-death” process frequently observed in eukaryotic genomes. Phylogenies provided no unequivocal evidence of horizontal gene transfer between the wasp host and the polydnavirus, but in some cases there were suggestions of such gene transfer.

Polydnavirus genomes reflect their dual roles as mutualists and pathogens

Symbionts often exhibit significant reductions in genome complexity while pathogens often exhibit increased complexity through acquisition and diversification of virulence determinants. A few organisms have evolved complex life cycles in which they interact as symbionts with one host and pathogens with another. How the predicted and opposing influences of symbiosis and pathogenesis affect genome evolution in such instances, however, is unclear. The Polydnaviridae is a family of double-stranded (ds) DNA viruses associated with parasitoid wasps that parasitize other insects. Polydnaviruses (PDVs) only replicate in wasps but infect and cause severe disease in parasitized hosts. This disease is essential for survival of the parasitoid's offspring. Thus, a true mutualism exists between PDVs and wasps as viral transmission depends on parasitoid survival and parasitoid survival depends on viral infection of the wasp's host. To investigate how life cycle and ancestry affect PDVs, we compared the genomes of Campoletis sonorensis ichnovirus ( CsIV) and Microplitis demolitor bracovirus ( MdBV). CsIV and MdBV have no direct common ancestor, yet their encapsidated genomes share several features including segmentation, diversification of virulence genes into families, and the absence of genes required for replication. In contrast, CsIV and MdBV share few genes expressed in parasitized hosts. We conclude that the similar organizational features of PDV genomes reflect their shared life cycle but that PDVs associated with ichneumonid and braconid wasps have likely evolved different strategies to cause disease in the wasp's host and promote parasitoid survival.

Tiny genomes and endoreduplication in Strepsiptera

Using flow cytometry, the genome sizes of two species of Strepsiptera were studied: that of male Caenocholax fenyesi texensis Kathirithamby & Johnston (Myrmecolacidae) at 108 Mb, which is the smallest insect genome documented to date; and those of male and female Xenos vesparum Rossi (Stylopidae), which are 1C = 130 and 133 Mb, respectively. The genome sizes of the following were analysed for comparative purposes: (a) the Hessian fly, Mayetiola destructor (Say), which was previously reported to be the smallest among insects: the male measured at 1C = 121 Mb and the female at 1C = 158 Mb; and (b) the female parasitic, haplodiploid, microhymenopteran wasp, Trichogramma brassicae Bezdenko, which measured at 1C = 246 Mb. The hosts of the strepsipterans were also measured: male Solenopsis invicta Buren, the red imported fire ant (host of male C. f. texensis), which is 1C = 753.3 Mb, and female Polistes dominulus Christ, the paper wasp (host of X. vesparum), is 1C = 301.4 Mb. Endoreduplication (4C) of the genome of the thorax of the male strepsipteran, and higher levels of endoduplication (4, 8, 16C) in the body of the larger female was observed. In contrast, little or no endoreduplication was observed, either in the Hessian fly, or in the parasitic wasp.

Commensal and mutualistic relationships of reoviruses with their parasitoid wasp hosts

During evolution, certain endoparasitoid wasps have developed mechanisms to suppress the defence systems of their hosts. For this purpose, these species, all of which belong to the families Ichneumonidae and Braconidae, inject various kinds of virus-like particles. The most studied of these particles are classified as polydnaviruses (family Polydnaviridae) which are symbiotic viruses. Over the past decade, it has also been shown that several wasp species harbour reoviruses (family Reoviridae), and that two of these suppress host defence, allowing the development of the parasitoid eggs. In this paper, we summarize the key features of these viruses and their relationships with their wasp hosts. Five reoviruses are known that appear to be non-pathogenic for the wasps. Three of these, McRVLP, HeRV, OpRVLP, use their wasp hosts as vectors, and do not appear to be involved in host defence suppression. The fourth, DpRV-1, is a commensal reovirus detected in most field populations of the wasp, Diadromus pulchellus. This reovirus is always found associated with an ascovirus, DpAV-4a, which is indispensable for host immune suppression. Although DpRV-1 has not been shown to directly increase D. pulchellus parasitic success, it may contribute to this success by retarding DpAV-4a replication in the wasp. The fifth reovirus, DpRV-2, occurs in a specific population of D. pulchellus in which DpRV-1 and DpAV-4 are absent. This virus has a mutualistic relationship with its wasp host, as its injection by females during oviposition is essential for host immunosuppression. Interestingly, these viruses belong to several different reovirus genera.

Poor control of the horse chestnut leafminer, Cameraria ohridella (Lepidoptera: Gracillariidae), by native European parasitoids: a synchronisation problem

Horse chestnut trees in many regions of Europe have suffered from epidemic infestations of C. ohridella for more than ten years. There has been no obvious decrease in the infestation level anywhere on the continent. One reason is, that the native natural enemies have not been able to control mass outbreaks of the leafminer. Parasitoid Hymenoptera have very little impact on the first generation of the moth in early summer, regardless of the number of parasitoids that overwintered in horse chestnut leaves. This study revealed that there is a considerable time lag between the emergence of the parasitoids from the leaflitter in spring and the appearance of suitable host instars in early summer. The poor control of C. ohridella by natural enemies may partly be due to the poor synchronisation between the life cycles of the introduced host and native parasitoid wasps.