Phylogeny and evolution of host-parasitoid interactions in hymenoptera

Comparative Analysis of the Venom Proteins from Two Eupelmid Egg Parasitoids Anastatus japonicus and Mesocomys trabalae

Parasitic wasps are abundant and diverse Hymenoptera insects that lay their eggs inside or on the external surface of the host and inject venom into the host to create a more favorable environment for the larvae to survive and regulate the host's immunity, metabolism, and development. But research on the composition of egg parasitoid venom is very limited. In this study, we used a combination of transcriptomic and proteomic approaches to identify the protein fractions of the venom in both eupelmid egg parasitoids, Anastatus japonicus and Mesocomys trabalae. We identified 3422 up-regulated venom gland genes (UVGs) in M. trabalae and 3709 in A. japonicus and analyzed their functions comparatively. By proteome sequencing, we identified 956 potential venom proteins in the venom pouch of M. trabalae, of which 186 were contained in UVGs simultaneously. A total of 766 proteins were detected in the venom of A. japonicus, of which 128 venom proteins were highly expressed in the venom glands. At the same time, the functional analysis of these identified venom proteins was carried out separately. We found the venom proteins in M. trabalae are well known but not in A. japonicus, which may be related to the host range. In conclusion, identifying venom proteins in both egg parasitoid species provides a database for studying the function of egg parasitoid venom and its parasitic mechanism.

The Amazon and Its Biodiversity: a Source of Unexplored Potential Natural Enemies for Biological Control (Predators and Parasitoids)

The Amazon is an important source of natural enemies for biological control. The diversity of biocontrol agents in the Amazon is considerably higher than that in other Brazilian regions. However, few studies have focused on the bioprospecting of natural enemies in the Amazon. Furthermore, the expansion of agricultural land in recent decades has caused biodiversity loss in the region, including the loss of potential biocontrol agents, due to the replacement of native forests with cultivated areas and forest degradation. In this study, we reviewed the main groups of natural enemies in the Brazilian Legal Amazon: predatory mites (mainly Acari: Phytoseiidae), ladybirds (Coleoptera: Coccinellidae), and social wasps (Hymenoptera: Vespidae: Polistinae) and the Hymenoptera parasitoids of eggs (Trichogrammatidae) and of frugivorous larvae (Braconidae and Figitidae). The main species prospected and used in biological control are presented. The lack of knowledge and perspectives regarding these groups of natural enemies as well as the challenges of conducting research in the Amazon is discussed.

Functional and Proteomic Insights into Aculeata Venoms

Aculeate hymenopterans use their venom for a variety of different purposes. The venom of solitary aculeates paralyze and preserve prey without killing it, whereas social aculeates utilize their venom in defence of their colony. These distinct applications of venom suggest that its components and their functions are also likely to differ. This study investigates a range of solitary and social species across Aculeata. We combined electrophoretic, mass spectrometric, and transcriptomic techniques to characterize the compositions of venoms from an incredibly diverse taxon. In addition, in vitro assays shed light on their biological activities. Although there were many common components identified in the venoms of species with different social behavior, there were also significant variations in the presence and activity of enzymes such as phospholipase A2s and serine proteases and the cytotoxicity of the venoms. Social aculeate venom showed higher presence of peptides that cause damage and pain in victims. The venom-gland transcriptome from the European honeybee (Apis mellifera) contained highly conserved toxins which match those identified by previous investigations. In contrast, venoms from less-studied taxa returned limited results from our proteomic databases, suggesting that they contain unique toxins.

Herbivory in Myrtillocactus geometrizans (Cactaceae): Do Parasitoids Provide Indirect Defense or a Direct Advantage?

Plants respond to herbivory in diverse, complex ways, ranging from avoidance or tolerance to indirect defense mechanisms such as attracting natural enemies of herbivores, i.e., parasitoids or predators, to strengthen their defense. Defense provided by parasitoids to cultivated plants is well documented and is used in biological control programs. However, its effectiveness on wild plants under natural conditions has been little studied. Such is the case of the cactus Myrtilllocactus geometrizans (known in Mexico as garambullo), which is consumed by the soft-scale insect Toumeyella martinezae (herbivore) which, in turn, is host to the parasitoid wasp Mexidalgus toumeyellus, and mutualist with the ant Liometopum apiculatum, that tenders and protects it. This study explores the role of the parasitoid as an indirect defense, by examining its effect on both the herbivore and the plant, and how this interaction is affected by the presence of the mutualistic ant. We found that scales adversely affect the cactus' growth, flower, and fruit production, as well as its progeny's performance, as seedlings from scale-infested garambullo plants were shorter, and it also favors the presence of fungus (sooty mold). The parasitoid responded positively to herbivore abundance, but the presence of ants reduced the intensity of parasitism. Our results show that parasitoids can function as an indirect defense, but their effectiveness is reduced by the presence of the herbivore's mutualistic ant.

Completely predatory development is described in a braconid wasp

Hymenopteran parasitoids are well known for their ubiquitous diversity, important ecological roles and biocontrol potential. We report the first detailed documentation of mite predation by a parasitoid wasp, Bracon predatorius Ranjith & Quicke sp. nov., (Insecta: Hymenoptera), first case of obligate predatory behaviour in the family Braconidae and first case of mite feeding within the superfamily Ichneumonoidea. Larvae of a new wasp species are shown to develop entirely as predators of eriophyid mites that induce leaf galls in a commercially important plant. They display highly modified head capsule morphology that we interpret as being associated with this atypical life style. We propose that the new feeding strategy evolved separately from recently described entomophytophagy in another species of the same genus. The divergent larval morphological adaptations of both species indicate a high degree of evolutionary developmental plasticity in the developmental stage.

A Short Review of the Venoms and Toxins of Spider Wasps (Hymenoptera: Pompilidae)

Parasitoid wasps represent the plurality of venomous animals, but have received extremely little research in proportion to this taxonomic diversity. The lion’s share of investigation into insect venoms has focused on eusocial hymenopterans, but even this small sampling shows great promise for the development of new active substances. The family Pompilidae is known as the spider wasps because of their reproductive habits which include hunting for spiders, delivering a paralyzing sting, and entombing them in burrows with one of the wasp’s eggs to serve as food for the developing larva. The largest members of this family, especially the tarantula hawks of the genus Pepsis, have attained notoriety for their large size, dramatic coloration, long-term paralysis of their prey, and incredibly painful defensive stings. In this paper we review the existing research regarding the composition and function of pompilid venoms, discuss parallels from other venom literatures, identify possible avenues for the adaptation of pompilid toxins towards human purposes, and future directions of inquiry for the field.

REVIEW OF THE DAUER HYPOTHESIS: WHAT NON-PARASITIC SPECIES CAN TELL US ABOUT THE EVOLUTION OF PARASITISM

Parasitic lineages have acquired suites of new traits compared to their nearest free-living relatives. When and why did these traits arise? We can envision lineages evolving through multiple stable intermediate steps such as a series of increasingly exploitative species interactions. This view allows us to use non-parasitic species that approximate those intermediate steps to uncover the timing and original function of parasitic traits, knowledge critical to understanding the evolution of parasitism. The dauer hypothesis proposes that free-living nematode lineages evolved into parasites through two intermediate steps, phoresy and necromeny. Here we delve into the proposed steps of the dauer hypothesis by collecting and organizing data from genetic, behavioral, and ecological studies in a range of nematode species. We argue that hypotheses on the evolution of parasites will be strengthened by complementing comparative genomic studies with ecological studies on non-parasites that approximate intermediate steps.

Sawfly Genomes Reveal Evolutionary Acquisitions That Fostered the Mega-Radiation of Parasitoid and Eusocial Hymenoptera

The tremendous diversity of Hymenoptera is commonly attributed to the evolution of parasitoidism in the last common ancestor of parasitoid sawflies (Orussidae) and wasp-waisted Hymenoptera (Apocrita). However, Apocrita and Orussidae differ dramatically in their species richness, indicating that the diversification of Apocrita was promoted by additional traits. These traits have remained elusive due to a paucity of sawfly genome sequences, in particular those of parasitoid sawflies. Here, we present comparative analyses of draft genomes of the primarily phytophagous sawfly Athalia rosae and the parasitoid sawfly Orussus abietinus. Our analyses revealed that the ancestral hymenopteran genome exhibited traits that were previously considered unique to eusocial Apocrita (e.g., low transposable element content and activity) and a wider gene repertoire than previously thought (e.g., genes for CO₂ detection). Moreover, we discovered that Apocrita evolved a significantly larger array of odorant receptors than sawflies, which could be relevant to the remarkable diversification of Apocrita by enabling efficient detection and reliable identification of hosts.

The origin of wing polyphenism in ants: An eco-evo-devo perspective

The evolution of eusociality, where solitary individuals integrate into a single colony, is a major transition in individuality. In ants, the origin of eusociality coincided with the origin of a wing polyphenism approximately 160 million years ago, giving rise to colonies with winged queens and wingless workers. As a consequence, both eusociality and wing polyphenism are nearly universal features of all ants. Here, we synthesize fossil, ecological, developmental, and evolutionary data in an attempt to understand the factors that contributed to the origin of wing polyphenism in ants. We propose multiple models and hypotheses to explain how wing polyphenism is orchestrated at multiple levels, from environmental cues to gene networks. Furthermore, we argue that the origin of wing polyphenism enabled the subsequent evolution of morphological diversity across the ants. We finally conclude by outlining several outstanding questions for future work.

Lipidomics reveals how the endoparasitoid wasp Pteromalus puparum manipulates host energy stores for its young

Endoparasitoid wasps inject venom along with their eggs to adjust the physiological and nutritional environment inside their hosts to benefit the development of their offspring. In particular, wasp venoms are known to modify host lipid metabolism, lipid storage in the fat body, and release of lipids into the hemolymph, but how venoms accomplish these functions remains unclear. Here, we use an UPLC-MS-based lipidomics approach to analyze the identities and concentrations of lipids in both fat body and hemolymph of host cabbage butterfly (Pieris rapae) infected by the pupal endoparasitoid Pteromalus puparum. During infection, host fat body levels of highly unsaturated, soluble triacylglycerides (TAGs) increased while less unsaturated, less soluble forms decreased. Furthermore, in infected host hemolymph, overall levels of TAG and phospholipids (the major component of cell membranes) increased, suggesting that fat body cells are destroyed and their contents are dispersed. Altogether, these data suggest that wasp venom induces host fat body TAGs to be transformed into lower melting point (more liquid) forms and released into the host hemolymph following infection, allowing simple absorption and nutritional acquisition by wasp larvae. Finally, cholesteryl esters (CEs, a dietary lipid derived from cholesterol) increased in host hemolymph following infection with no concomitant decrease in host cholesterol, implying that the wasp may provide this necessary food resource to its offspring via its venom. This study provides novel insight into how parasitoid infection alters lipid metabolism in insect hosts, and begins to uncover the wasp venom proteins responsible for host physiological changes and offspring development.

Proteo-Transcriptomic Characterization of the Venom from the Endoparasitoid Wasp Pimpla turionellae with Aspects on Its Biology and Evolution

Within mega-diverse Hymenoptera, non-aculeate parasitic wasps represent 75% of all hymenopteran species. Their ovipositor dual-functionally injects venom and employs eggs into (endoparasitoids) or onto (ectoparasitoids) diverse host species. Few endoparasitoid wasps such as Pimpla turionellae paralyze the host and suppress its immune responses, such as encapsulation and melanization, to guarantee their offspring's survival. Here, the venom and its possible biology and function of P. turionellae are characterized in comparison to the few existing proteo-transcriptomic analyses on parasitoid wasp venoms. Multiple transcriptome assembly and custom-tailored search and annotation strategies were applied to identify parasitoid venom proteins. To avoid false-positive hits, only transcripts were finally discussed that survived strict filter settings, including the presence in the proteome and higher expression in the venom gland. P. turionella features a venom that is mostly composed of known, typical parasitoid enzymes, cysteine-rich peptides, and other proteins and peptides. Several venom proteins were identified and named, such as pimplin2, 3, and 4. However, the specification of many novel candidates remains difficult, and annotations ambiguous. Interestingly, we do not find pimplin, a paralytic factor in Pimpla hypochondriaca, but instead a new cysteine inhibitor knot (ICK) family (pimplin2), which is highly similar to known, neurotoxic asilid1 sequences from robber flies.

The genomes of two parasitic wasps that parasitize the diamondback moth

BACKGROUND

Parasitic insects are well-known biological control agents for arthropod pests worldwide. They are capable of regulating their host's physiology, development and behaviour. However, many of the molecular mechanisms involved in host-parasitoid interaction remain unknown.

RESULTS

We sequenced the genomes of two parasitic wasps (Cotesia vestalis, and Diadromus collaris) that parasitize the diamondback moth Plutella xylostella using Illumina and Pacbio sequencing platforms. Genome assembly using SOAPdenovo produced a 178 Mb draft genome for C. vestalis and a 399 Mb draft genome for D. collaris. A total set that contained 11,278 and 15,328 protein-coding genes for C. vestalis and D. collaris, respectively, were predicted using evidence (homology-based and transcriptome-based) and de novo prediction methodology. Phylogenetic analysis showed that the braconid C. vestalis and the ichneumonid D. collaris diverged approximately 124 million years ago. These two wasps exhibit gene gains and losses that in some cases reflect their shared life history as parasitic wasps and in other cases are unique to particular species. Gene families with functions in development, nutrient acquisition from hosts, and metabolism have expanded in each wasp species, while genes required for biosynthesis of some amino acids and steroids have been lost, since these nutrients can be directly obtained from the host. Both wasp species encode a relative higher number of neprilysins (NEPs) thus far reported in arthropod genomes while several genes encoding immune-related proteins and detoxification enzymes were lost in both wasp genomes.

CONCLUSIONS

We present the annotated genome sequence of two parasitic wasps C. vestalis and D. collaris, which parasitize a common host, the diamondback moth, P. xylostella. These data will provide a fundamental source for studying the mechanism of host control and will be used in parasitoid comparative genomics to study the origin and diversification of the parasitic lifestyle.

Arthropod venoms: Biochemistry, ecology and evolution

Comprising of over a million described species of highly diverse invertebrates, Arthropoda is amongst the most successful animal lineages to have colonized aerial, terrestrial, and aquatic domains. Venom, one of the many fascinating traits to have evolved in various members of this phylum, has underpinned their adaptation to diverse habitats. Over millions of years of evolution, arthropods have evolved ingenious ways of delivering venom in their targets for self-defence and predation. The morphological diversity of venom delivery apparatus in arthropods is astounding, and includes extensively modified pedipalps, tail (telson), mouth parts (hypostome), fangs, appendages (maxillulae), proboscis, ovipositor (stinger), and hair (urticating bristles). Recent investigations have also unravelled an astonishing venom biocomplexity with molecular scaffolds being recruited from a multitude of protein families. Venoms are a remarkable bioresource for discovering lead compounds in targeted therapeutics. Several components with prospective applications in the development of advanced lifesaving drugs and environment friendly bio-insecticides have been discovered from arthropod venoms. Despite these fascinating features, the composition, bioactivity, and molecular evolution of venom in several arthropod lineages remains largely understudied. This review highlights the prevalence of venom, its mode of toxic action, and the evolutionary dynamics of venom in Arthropoda, the most speciose phylum in the animal kingdom.

Parasitoid biology preserved in mineralized fossils

About 50% of all animal species are considered parasites. The linkage of species diversity to a parasitic lifestyle is especially evident in the insect order Hymenoptera. However, fossil evidence for host–parasitoid interactions is extremely rare, rendering hypotheses on the evolution of parasitism assumptive. Here, using high-throughput synchrotron X-ray microtomography, we examine 1510 phosphatized fly pupae from the Paleogene of France and identify 55 parasitation events by four wasp species, providing morphological and ecological data. All species developed as solitary endoparasitoids inside their hosts and exhibit different morphological adaptations for exploiting the same hosts in one habitat. Our results allow systematic and ecological placement of four distinct endoparasitoids in the Paleogene and highlight the need to investigate ecological data preserved in the fossil record.

Evidence for a parasitic lifestyle in extinct species tends to be indirect. Here, the authors provide direct evidence through X-ray examination of approximately 30–40 million year old fossil fly pupae, revealing 55 parasitation events by four newly described wasp species.

First extensive characterization of the venom gland from an egg parasitoid: structure, transcriptome and functional role

The venom gland is a ubiquitous organ in Hymenoptera. In insect parasitoids, the venom gland has been shown to have multiple functions including regulation of host immune response, host paralysis, host castration and developmental alteration. However, the role played by the venom gland has been mainly studied in parasitoids developing in larval or pupal hosts while little is known for parasitoids developing in insect eggs. We conducted the first extensive characterization of the venom of the endoparasitoid Ooencyrtus telenomicida (Vassiliev), a species that develops in eggs of the stink bug Nezara viridula (L.). In particular we investigated the structure of the venom apparatus, its functional role and conducted a transcriptomic analysis of the venom gland. We found that injection of O. telenomicida venom induces: 1) a melanized-like process in N. viridula host eggs (host-parasitoid interaction), 2) impairment of the larval development of the competitor Trissolcus basalis (Wollaston) (parasitoid-parasitoid interaction). The O. telenomicida venom gland transcriptome reveals a majority of digestive enzymes (peptidases and glycosylases) and oxidoreductases (laccases) among the most expressed genes. The former enzymes are likely to be involved in degradation of the host resources for the specific benefit of the O. telenomicida offspring. In turn, alteration of host resources caused by these enzymes may negatively affect the larval development of the competitor T. basalis. We hypothesize that the melanization process induced by venom injection could be related to the presence of laccases, which are multicopper oxidases that belong to the phenoloxidases group. This work contributed to a better understanding of the venom in insect parasitoids and allowed to identify candidate genes whose functional role can be investigated in future studies.

In silico prediction of neuropeptides in Hymenoptera parasitoid wasps

Parasitoid wasps of the order Hymenoptera, the most diverse groups of animals, are important natural enemies of arthropod hosts in natural ecosystems and can be used in biological control. To date, only one neuropeptidome of a parasitoid wasp, Nasonia vitripennis, has been identified. This study aimed to identify more neuropeptides of parasitoid wasps, by using a well-established workflow that was previously adopted for predicting insect neuropeptide sequences. Based on publicly accessible databases, totally 517 neuropeptide precursors from 24 parasitoid wasp species were identified; these included five neuropeptides (CNMamide, FMRFamide-like, ITG-like, ion transport peptide-like and orcokinin B) that were identified for the first time in parasitoid wasps, to our knowledge. Next, these neuropeptides from parasitoid wasps were compared with those from other insect species. Phylogenetic analysis suggested the divergence of AST-CCC within Hymenoptera. Further, the encoding patterns of CAPA/PK family genes were found to be different between Hymenoptera species and other insect species. Some neuropeptides that were not found in some parasitoid superfamilies (e.g., sulfakinin), or considerably divergent between different parasitoid superfamilies (e.g., sNPF) might be related to distinct physiological processes in the parasitoid life. Information of neuropeptide sequences in parasitoid wasps can be useful for better understanding the phylogenetic relationships of Hymenoptera and further elucidating the physiological functions of neuropeptide signaling systems in parasitoid wasps.

WaspBase: a genomic resource for the interactions among parasitic wasps, insect hosts and plants

Insect pests reduce yield and cause economic losses, which are major problems in agriculture. Parasitic wasps are the natural enemies of many agricultural pests and thus have been widely used as biological control agents. Plants, phytophagous insects and parasitic wasps form a tritrophic food chain. Understanding the interactions in this tritrophic system should be helpful for developing parasitic wasps for pest control and deciphering the mechanisms of parasitism. However, the genomic resources for this tritrophic system are not well organized. Here, we describe the WaspBase, a new database that contains 573 transcriptomes of 35 parasitic wasps and the genomes of 12 parasitic wasps, 5 insect hosts and 8 plants. In addition, we identified long non-coding RNA, untranslated regions and 25 widely studied gene families from the genome and transcriptome data of these species. WaspBase provides conventional web services such as Basic Local Alignment Search Tool, search and download, together with several widely used tools such as profile hidden Markov model, Multiple Alignment using Fast Fourier Transform, automated alignment trimming and JBrowse. We also present a collection of active researchers in the field of parasitic wasps, which should be useful for constructing scientific networks in this field.

Paleobiology of Predators, Parasitoids, and Parasites: Death and Accomodation in the Fossil Record of Continental Invertebrates

Carnivory is the consumption of one animal by another animal; among invertebrates in terrestrial and freshwater ecosystems this type of feeding can take three forms: predation, parasitoidism, and parasitism. Differences among these three functional modes involve (i) whether the duration of feeding on the prey item is quick or there is an accommodation, coevolutionary or otherwise, between the carnivore and the host prey; (ii) whether the prey or host is killed; (iii) whether single or multiple prey or host items are consumed during the carnivore's lifespan, and (iv) the relative sizes of the carnivore and its prey or host. Uniformitarian and nonuniformitarian evidence directly relating to the history of carnivory can be found in exceptionally preserved deposits from the mid-Paleozoic to the Recent, but such evidence is relatively rare because carnivores are the least represented trophic group in ecosystems. Six types of paleobiological data provide evidence for carnivory: taxonomic affiliation, fossil structural and functional attributes, organismic damage, gut contents, coprolites, and indications of mechanisms for predator avoidance.

Only 12 invertebrate phyla have become carnivorous in the continental realm. Six are lophotrochozoans (Acanthocephala, Rotifera, Platyhelminthes, Nemertinea, Mollusca, and Annelida) and six are ecdysozoans (Nematoda, Nematomorpha, Tardigrada, Onychophora, Pentastoma, and Arthropoda). Most of these groups have poor continental fossil records, but the two most diverse—nematodes and arthropods—have comparatively good representation. The record of arthropods documents (i) the presence of predators among primary producers, herbivores, and decomposers in early terrestrial ecosystems; (ii) the addition later in the fossil record of the more accommodationist strategies of parasitoids and parasites interacting with animal hosts; (iii) the occurrence of simpler food-web structures in terrestrial ecosystems prior to parasitoid and parasite diversification; and (iv) a role for mass extinction in the degradation of food-web structure that ultimately affected carnivory. Future research should explore how different modes of carnivory have brought about changes in ecosystem structure through time. Despite numerous caveats and uncertainties, trace fossils left by predators on skeletons of their prey remain one of the most promising research directions in paleoecology and evolutionary paleobiology.

Comparative transcriptome analysis of venom glands from Cotesia vestalis and Diadromus collaris, two endoparasitoids of the host Plutella xylostella

Venoms secreted by the venom gland (VG) of parasitoid wasp help ensure successful parasitism by host immune suppression and developmental regulation. Cotesia vestalis, a larval endoparasitoid, and Diadromus collaris, a pupal endoparasitoid, parasitize the diamondback moth (DBM), Plutella xylostella. To explore and compare the venom components of two endoparasitoids, we sequenced transcriptomes of the VGs and wasp bodies without VGs (BWVGs) of the two endoparasitoids. Statistically enriched GO terms and KEGG pathways of the two VGs compared to respective whole-body background were similar and reflected active protein biosynthesis activities in the two VGs. 1,595 VG specific genes of the D. collaris VG and 1,461 VG specific genes of the C. vestalis VG were identified by comparative transcript profiling. A total of 444 and 513 genes encoding potential secretory proteins were identified and defined as putative venom genes in D. collaris VG and C. vestalis VG, respectively. The putative venom genes of the two wasps showed no significant similarity or convergence. More venom genes were predicted in D. collaris VG than C. vestalis VG, especially hydrolase-coding genes. Differences in the types and quantities of putative venom genes shed light on different venom functions.

De novo sequencing and transcriptome analysis of venom glands of endoparasitoid Aenasius arizonensis (Girault) (=Aenasius bambawalei Hayat) (Hymenoptera, Encyrtidae)

Aenasius bambawalei Hayat (Encyrtidae: Hymenoptera) has been synonymized with Aenasius arizonensis (Girault) is a small, newly discovered endoparasitoid of the cotton mealybug Phenacoccuss solenopsis Tinsley (Pseudococcidae: Hemiptera), which completes its life cycle inside the body of its host and it is a potential insect control tool. Despite the acquired knowledge regarding host-parasitoid interaction, little information is available on the factors of parasitoid origin able to modulate mealybug physiology. The components of A. arizonensis venom have not been well studied but venom from other parasitoids and wasps contain biologically active proteins that have potential applications in pest management or may be of medicinal importance. To provide an insight into the transcripts expressed in the venom gland of A. arizonensis, a transcriptomic database was developed utilizing high throughput RNA sequencing approaches to analyze the genes expressed in venom glands of this endoparasitic wasp. The resulting A. arizonensis RNA sequences were assembled de-novo with contigs then blasted against the NCBI non-redundant sequence database. Contigs which matched database sequences were mostly homologous to genes from hymenopteran parasitoids such as Nasonia vitripennis, Copidosoma floridanum, Fopius arsenus and Pteromalas puparium. Further analysis of the A. arizonensis database was then performed which focused on selected genes encoding proteins potentially involved in host developmental arrest, disrupting the host immune system, host paralysis, and transcripts that support these functions. Sequenced mRNAS predicted to encode full length ORFs of Calreticulin, Serine Protease Precursor and Arginine kinase proteins were identified and the tissue specific expression of these putative venom genes was analyzed by RT-PCR. In addition, results also demonstrate that de novo transcriptome assembly allows useful venom gene expression analysis in a species lacking a genome sequence database and may provide useful information for devising control tools for insect pests and other applications.

De novo sequencing and transcriptome analysis of female venom glands of ectoparasitoid Bracon hebetor (Say.) (Hymenoptera: Braconidae)

Venom is a key-factor in the regulation of host physiology by parasitic Hymenoptera and a potentially rich source of novel bioactive substances for biotechnological applications. The limited study of venom from the ectoparasitoid Bracon hebetor, a tiny wasp that attacks larval pest insects of field and stored products and is thus a potential insect control agent, has not described the full complement and composition of these biomolecules. To have a comprehensive picture of genes expressed in the venom glands of B. hebetor, a venom gland transcriptome was assembled by using next generation sequencing technologies followed by de novo assemblies of the 10.81 M sequence reads yielded 22,425 contigs, of which 10,581 had significant BLASTx hits to know genes. The majority of hits were to Diachasma alloeum, an ectoparasitoid from same taxonomic family, as well as other wasps. Gene ontology grouped the sequences into molecular functions in which catalytic activity with 42.2% was maximum, cellular components in which cells with 33.8% and biological processes among which metabolic process with 30% had the most representatives. In this study, we highlight the most abundant sequences, and those that are likely to be functional components of the venom for parasitization. Full length ORFs of Calreticulin, Venom Acid Phosphatase Acph-1 like protein and arginine kinase proteins were isolated and their tissue specific expression was studied by RT-PCR. Our report is the first to characterize components of the B. hebetor venom glands that may be useful for developing control tools for insect pests and other applications.

Analysis of Genetic Variation across the Encapsidated Genome of Microplitis demolitor Bracovirus in Parasitoid Wasps

Insect parasitoids must complete part of their life cycle within or on another insect, ultimately resulting in the death of the host insect. One group of parasitoid wasps, the ‘microgastroid complex’ (Hymenoptera: Braconidae), engage in an association with beneficial symbiotic viruses that are essential for successful parasitism of hosts. These viruses, known as Bracoviruses, persist in an integrated form in the wasp genome, and activate to replicate in wasp ovaries during development to ultimately be delivered into host insects during parasitism. The lethal nature of host-parasitoid interactions, combined with the involvement of viruses in mediating these interactions, has led to the hypothesis that Bracoviruses are engaged in an arms race with hosts, resulting in recurrent adaptation in viral (and host) genes. Deep sequencing was employed to characterize sequence variation across the encapsidated Bracovirus genome within laboratory and field populations of the parasitoid wasp species Microplitis demolitor. Contrary to expectations, there was a paucity of evidence for positive directional selection among virulence genes, which generally exhibited signatures of purifying selection. These data suggest that the dynamics of host-parasite interactions may not result in recurrent rounds of adaptation, and that adaptation may be more variable in time than previously expected.

Cotesia vestalis teratocytes express a diversity of genes and exhibit novel immune functions in parasitism

Some endoparasitoid wasps lay eggs that produce cells called teratocytes. In this study, we sequenced and analyzed the transcriptome of teratocytes from the solitary endoparasitoid Cotesia vestalis (Braconidae), which parasitizes larval stage Plutella xylostella (Plutellidae). Results identified many teratocyte transcripts with potential functions in affecting host immune defenses, growth or metabolism. Characterization of teratocyte-secreted venom-like protein 8 (TSVP-8) indicated it inhibits melanization of host hemolymph in vitro, while two predicted anti-microbial peptides (CvT-def 1 and 3) inhibited the growth of bacteria. Results also showed the parasitized hosts lacking teratocytes experienced higher mortality after immune challenge by pathogens than hosts with teratocytes. Taken together, these findings indicate that C. vestalis teratocytes secrete products that alter host immune functions while also producing anti-microbial peptides with functions that help protect the host from infection by other organisms.

Evidence for common horizontal transmission of Wolbachia among butterflies and moths

Background

Wolbachia is one of the most widespread bacteria on Earth. Previous research on Wolbachia-host interactions indicates that the bacterium is typically transferred vertically, from mother to offspring, through the egg cytoplasm. Although horizontal transmission of Wolbachia from one species to another is reported to be common in arthropods, limited direct ecological evidence is available. In this study, we examine horizontal transmission of Wolbachia using a multilocus sequence typing (MLST) strains dataset and used Wolbachia and Lepidoptera genomes to search for evidence for lateral gene transfer (LGT) in Lepidoptera, one of the most diverse cosmopolitan insect orders. We constructed a phylogeny of arthropod-associated MLST Wolbachia strains and calibrated the age of Wolbachia strains associated with lepidopteran species.

Results

Our results reveal inter-specific, inter-generic, inter-familial, and inter-ordinal horizontal transmission of Wolbachia strains, without discernible geographic patterns. We found at least seven probable cases of horizontal transmission among 31 species within Lepidoptera and between Lepidoptera and other arthropod hosts. The divergence time analysis revealed that Wolbachia is recently (22.6–4.7 mya, 95 % HPD) introduced in Lepidoptera. Analysis of nine Lepidoptera genomes (Bombyx mori, Danaus plexippus, Heliconius melpomene, Manduca sexta, Melitaea cinxia, Papilio glaucus, P. polytes, P. xuthus and Plutella xylostella) yielded one possible instance of Wolbachia LGT.

Conclusions

Our results provide evidence of high incidence of identical and multiple strains of Wolbachia among butterflies and moths, adding Lepidoptera to the growing body of evidence for common horizontal transmission of Wolbachia. This study demonstrates interesting dynamics of this remarkable and influential microorganism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0660-x) contains supplementary material, which is available to authorized users.

Community ecology of the 'other' parasitoids

The study of parasitoid communities is an active and dynamic field. Most studies, however, are focused primarily on parasitic wasps, despite the thousands of other insect parasitoids distributed across many lineages. Although questions in parasitoid community ecology are much the same for different groups, answers to these questions may not be due to differing biological traits. The ecology of non-hymenopteran ('NH') parasitoid communities is poorly known, but recent work indicates that habitat and host traits have strong impacts on the size and composition of these parasitoid assemblages. Recent food-web analyses indicate that host ranges vary widely within and among taxa and associations are shaped by host ecology and defenses. Evidence is also accumulating for strong 'bottom-up' and 'top-down' multi-trophic interactions between NH-parasitoids and nonadjacent trophic levels, as well as trait-mediated indirect effects on communities. Recent technical and conceptual advances in characterizing and comparing food webs, consideration of phylogenetic history, and increasing anthropogenic impacts provide many new and stimulating areas of research on parasitoid communities.

Polydnaviruses: Nature's Genetic Engineers

Virus-host associations are usually viewed as parasitic, but several studies in recent years have reported examples of viruses that benefit host organisms. The Polydnaviridae are of particular interest because these viruses are all obligate mutualists of insects called parasitoid wasps. Parasitoids develop during their immature stages by feeding inside the body of other insects, which serve as their hosts. Polydnaviruses are vertically transmitted as proviruses through the germ line of wasps but also function as gene delivery vectors that wasps rely upon to genetically manipulate the hosts they parasitize. Here we review the evolutionary origin of polydnaviruses, the organization and function of their genomes, and some of their roles in parasitism.

Insights into the venom composition and evolution of an endoparasitoid wasp by combining proteomic and transcriptomic analyses

Parasitoid wasps are abundant and diverse hymenopteran insects that lay their eggs into the internal body (endoparasitoid) or on the external surface (ectoparasitoid) of their hosts. To make a more conducive environment for the wasps’ young, both ecto- and endoparasitoids inject venoms into the host to modulate host immunity, metabolism and development. Endoparasitoids have evolved from ectoparasitoids independently in different hymenopteran lineages. Pteromalus puparum, a pupal endoparasitoid of various butterflies, represents a relatively recent evolution of endoparasitism within pteromalids. Using a combination of transcriptomic and proteomic approaches, we have identified 70 putative venom proteins in P. puparum. Most of them show higher similarity to venom proteins from the related ectoparasitoid Nasonia vitripennis than from other more distantly related endoparasitoids. In addition, 13 venom proteins are similar to venoms of distantly related endoparasitoids but have no detectable venom matches in Nasonia. These venom proteins may have a role in adaptation to endoparasitism. Overall, these results lay the groundwork for more detailed studies of venom function and adaptation to the endoparasitic lifestyle.

An endoparasitoid Cretaceous fly and the evolution of parasitoidism

Parasitoidism is a key innovation in insect evolution, and parasitoid insects, nowadays, play a significant role in structuring ecological communities. Despite their diversity and ecological impact, little is known about the early evolution and ecology of parasitoid insects, especially parasitoid true flies (Diptera). Here, we describe a bizarre fly, Zhenia xiai gen. et sp. nov., from Late Cretaceous Burmese amber (about 99 million years old) that represents the latest occurrence of the family Eremochaetidae. Z. xiai is an endoparasitoid insect as evidenced by a highly developed, hypodermic-like ovipositor formed by abdominal tergites VIII + IX that was used for injecting eggs into hosts and enlarged tridactylous claws supposedly for clasping hosts. Our results suggest that eremochaetids are among the earliest definite records of parasitoid insects. Our findings reveal an unexpected morphological specialization of flies and broaden our understanding of the evolution and diversity of ancient parasitoid insects.

A new approach for investigating venom function applied to venom calreticulin in a parasitoid wasp

A new method is developed to investigate functions of venom components, using venom gene RNA interference knockdown in the venomous animal coupled with RNA sequencing in the envenomated host animal. The vRNAi/eRNA-Seq approach is applied to the venom calreticulin component (v-crc) of the parasitoid wasp Nasonia vitripennis. Parasitoids are common, venomous animals that inject venom proteins into host insects, where they modulate physiology and metabolism to produce a better food resource for the parasitoid larvae. vRNAi/eRNA-Seq indicates that v-crc acts to suppress expression of innate immune cell response, enhance expression of clotting genes in the host, and up-regulate cuticle genes. V-crc KD also results in an increased melanization reaction immediately following envenomation. We propose that v-crc inhibits innate immune response to parasitoid venom and reduces host bleeding during adult and larval parasitoid feeding. Experiments do not support the hypothesis that v-crc is required for the developmental arrest phenotype observed in envenomated hosts. We propose that an important role for some venom components is to reduce (modulate) the exaggerated effects of other venom components on target host gene expression, physiology, and survival, and term this venom mitigation. A model is developed that uses vRNAi/eRNA-Seq to quantify the contribution of individual venom components to total venom phenotypes, and to define different categories of mitigation by individual venoms on host gene expression. Mitigating functions likely contribute to the diversity of venom proteins in parasitoids and other venomous organisms.

Trends in genome dynamics among major orders of insects revealed through variations in protein families

Background

Insects belong to a class that accounts for the majority of animals on earth. With over one million identified species, insects display a huge diversity and occupy extreme environments. At present, there are dozens of fully sequenced insect genomes that cover a range of habitats, social behavior and morphologies. In view of such diverse collection of genomes, revealing evolutionary trends and charting functional relationships of proteins remain challenging.

Results

We analyzed the relatedness of 17 complete proteomes representative of proteomes from insects including louse, bee, beetle, ants, flies and mosquitoes, as well as an out-group from the crustaceans. The analyzed proteomes mostly represented the orders of Hymenoptera and Diptera. The 287,405 protein sequences from the 18 proteomes were automatically clustered into 20,933 families, including 799 singletons. A comprehensive analysis based on statistical considerations identified the families that were significantly expanded or reduced in any of the studied organisms. Among all the tested species, ants are characterized by an exceptionally high rate of family gain and loss. By assigning annotations to hundreds of species-specific families, the functional diversity among species and between the major clades (Diptera and Hymenoptera) is revealed. We found that many species-specific families are associated with receptor signaling, stress-related functions and proteases. The highest variability among insects associates with the function of transposition and nucleic acids processes (collectively coined TNAP). Specifically, the wasp and ants have an order of magnitude more TNAP families and proteins relative to species that belong to Diptera (mosquitoes and flies).

Conclusions

An unsupervised clustering methodology combined with a comparative functional analysis unveiled proteomic signatures in the major clades of winged insects. We propose that the expansion of TNAP families in Hymenoptera potentially contributes to the accelerated genome dynamics that characterize the wasp and ants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1771-2) contains supplementary material, which is available to authorized users.

Wolbachia in butterflies and moths: geographic structure in infection frequency

INTRODUCTION

Butterflies and moths (Lepidoptera) constitute one of the most diverse insect orders, and play an important role in ecosystem function. However, little is known in terms of their bacterial communities. Wolbachia, perhaps the most common and widespread intracellular bacterium on Earth, can manipulate the physiology and reproduction of its hosts, and is transmitted vertically from mother to offspring, or sometimes horizontally between species. While its role in some hosts has been studied extensively, its incidence across Lepidoptera is poorly understood. A recent analysis using a beta-binomial model to infer the between-species distribution of prevalence estimated that approximately 40 % of arthropod species are infected with Wolbachia, but particular taxonomic groups and ecological niches seem to display substantially higher or lower incidences. In this study, we took an initial step and applied a similar, maximum likelihood approach to 300 species of Lepidoptera (7604 individuals from 660 populations) belonging to 17 families and 10 superfamilies, and sampled from 36 countries, representing all continents excluding Antarctica.

RESULTS

Approximately a quarter to a third of individuals appear to be infected with Wolbachia, and around 80 % of Lepidoptera species are infected at a non-negligible frequency. This incidence estimate is very high compared to arthropods in general. Wolbachia infection in Lepidoptera is shown to vary between families, but there is no evidence for closely related groups to show similar infection levels. True butterflies (Papilionoidea) are overrepresented in our data, however, our estimates show this group can be taken as a representative for the other major lepidopteran superfamilies. We also show substantial variation in infection level according to geography - closer locations tend to show similar infection levels. We further show that variation in geography is due to a latitudinal gradient in Wolbachia infection, with lower frequencies towards higher latitudes.

CONCLUSIONS

Our comprehensive survey of Wolbachia infection in Lepidoptera suggests that infection incidence is very high, and provides evidence that climate and geography are strong predictors of infection frequency.

Reversion of developmental mode in insects: evolution from long germband to short germband in the polyembrionic wasp Macrocentrus cingulum Brischke

Germband size in insects has played a central role in our understanding of insect patterning mechanisms and their evolution. The polarity of evolutionary change in insect patterning has been viewed so far as the unidirectional shift from the ancestral short germband patterning of basal hemimetabolous insects to the long germband patterning observed in most modern Holometabola. However, some orders of holometabolic insects display both short and long germband development, though the absence of a clear phylogenetic context does not permit definite conclusions on the polarity of change. Derived hymenoptera, that is, bees and wasps, represent a classical textbook example of long germband development. Yet, in some wasps putative short germband development has been described correlating with lifestyle changes, namely with evolution of endoparasitism and polyembryony. To address the potential reversion from long to short germband, we focused on the family Braconidae, which displays ancestral long germband development, and examined the derived polyembryonic braconid Macrocentrus cingulum. Using SEM analysis of M. cingulum embryogenesis coupled with analyses of embryonic patterning markers, we show that this wasp evolved short germband embryogenesis secondarily, in a way that is reminiscent of embryogenesis in the beetle Tribolium castaneum. This work shows that the evolution of germband size in insects is a reversible process that may correlate with other life-history traits and suggests broader implications on the mechanisms and evolvability of insect development.

Functional and Taxonomic Diversity of Stinging Wasps in Brazilian Atlantic Rainforest Areas

Vespoidea are the most functionally diverse superfamily of Hymenoptera. Ecological studies involving this family are primarily based on eusocial groups, including ants and social paper wasps. In the present study, we examine stinging wasp (Vespoidea) faunal diversity in the Atlantic Rain Forest, which is one of the most diverse and threatened ecosystems in the World. Three conservation areas were sampled employing a standardized sample protocol. Families and functional groups of Vespoidea were collected in each area, with the exception ants (Formicidae), and analyzed using diversity analyses, to generate taxonomic diversity and distinctness indices. Results indicated Pompilidae was the most diverse family, and the idiobiont parasitoid type was the most diverse functional group in the three study areas. Núcleo Picinguaba of the Parque Estadual da Serra do Mar was taxonomically and functionally the most diverse and species rich area. Parque Estadual Intervales showed the highest number of dominant species and diversity of koinobiont parasitoids, while the Rebio Sooretama exhibited a decrease in several diversity parameters.

Venom gland extract is not required for successful parasitism in the polydnavirus-associated endoparasitoid Hyposoter didymator (Hym. Ichneumonidae) despite the presence of numerous novel and conserved venom proteins

The venom gland is a conserved organ in Hymenoptera that shows adaptations associated with life-style diversification. Few studies have investigated venom components and function in the highly diverse parasitic wasps and all suggest that the venom regulates host physiology. We explored the venom of the endoparasitoid Hyposoter didymator (Campopleginae), a species with an associated polydnavirus produced in the ovarian tissue. We investigated the effects of the H. didymator venom on two physiological traits of the host Spodoptera frugiperda (Noctuidae): encapsulation response and growth rate. We found that H. didymator venom had no significant effect on host cellular immunity or development, suggesting that it does not contribute to parasitism success. The host physiology seemed to be modified essentially by the ovarian fluid containing the symbiotic polydnaviruses. Proteomic analyses indicated that the H. didymator venom gland produces a large variety of proteins, consistent with the classical hymenopteran venom protein signature, including: reprolysin-like, dipeptidyl peptidase IV, hyaluronidase, arginine kinase or allergen proteins. The venom extracts also contained novel proteins, encoded by venom genes conserved in Campopleginae ichneumonids, and proteins with similarities to active molecules identified in other parasitoid species, such as calreticulin, reprolysin, superoxide dismutase and serpin. However, some of these proteins appear to be produced only in small amounts or to not be secreted. Possibly, in Campopleginae carrying polydnaviruses, the host-modifying activities of venom became redundant following the acquisition of polydnaviruses by the lineage.

Polydnaviruses of Parasitic Wasps: Domestication of Viruses To Act as Gene Delivery Vectors

Symbiosis is a common phenomenon in which associated organisms can cooperate in ways that increase their ability to survive, reproduce, or utilize hostile environments. Here, we discuss polydnavirus symbionts of parasitic wasps. These viruses are novel in two ways: (1) they have become non-autonomous domesticated entities that cannot replicate outside of wasps; and (2) they function as a delivery vector of genes that ensure successful parasitism of host insects that wasps parasitize. In this review we discuss how these novelties may have arisen, which genes are potentially involved, and what the consequences have been for genome evolution.

The many roads to parasitism: a tale of convergence

Parasitic organisms account for a large portion of living species. They have arisen on multiple independent occasions in many phyla, and thus encompass a huge biological diversity. This review uses several lines of evidence to argue that this vast diversity can be reduced to a few evolutionary end points that transcend phylogenetic boundaries. These represent peaks in the adaptive landscape reached independently by different lineages undergoing convergent evolution. Among eukaryotic parasites living in or on animals, six basic parasitic strategies are identified based on the number of hosts used per parasite generation, the fitness loss incurred by the host, and the transmission routes used by the parasites. They are parasitoids, parasitic castrators, directly transmitted parasites, trophically transmitted parasites, vector-transmitted parasites and micropredators. These show evidence of convergence in morphology, physiology, reproduction, life cycles and transmission patterns. Parasite-host body size ratios, and the relationship between virulence and intensity of infection, are also associated with the different parasitic strategies, but not consistently so. At the population level, patterns of parasite distribution among hosts are not uniform across all parasitic strategies, but are distinctly different for parasitoids and castrators than for other parasites. To demonstrate that the above six strategies defined for animal parasites are universal, comparisons are made with parasites of plants, in particular, plant-parasitic nematodes and parasitic angiosperms; these are shown to follow the same evolutionary trajectories seen among animal parasites, despite huge physiological and ecological differences between animals and plants. Beyond demonstrating the inevitable convergence of disparate lineages across biological hyperspace towards a limited set of adaptive strategies, this synthesis also provides a unifying framework for the study of parasitism.

Per arborem ad astra: morphological adaptations to exploiting the woody habitat in the early evolution of Hymenoptera

We survey morphological features of larval and adult wasps that undergo their entire larval development inside wood and interpret them in view of the lifestyle. The evolution of some of the characters is explored by mapping them on a recently published phylogeny of Hymenoptera. Based on this phylogeny, it is reasonable to assume that wood-living wasps evolved from a xylophagous/mycetophagous stage as displayed by woodwasps to a carnivorous/parasitoid lifestyle, preying on woodboring insect larvae. The latter mode of life is probably ancestral to the Apocrita which comprise the majority of the order; they share this lifestyle with their sister group, the Orussidae. However, most apocritan wasps have radiated into other habitats, the Orussidae and Stephanidae apparently being the only taxa that have retained the ancestral lifestyle of carnivorous wasps. Other apocritan lineages associated with wood (e.g., Aulacidae, Megalyridae, basal Cynipoidea and some Ichneumonoidea and Chalcidoidea) possibly entered this habitat secondarily and independently acquired morphological traits associated with it. The woody habitat was occupied by Hymenoptera during a crucial stage in their evolution where the transition from the phytophagous to carnivorous lifestyle took place. The anatomy of both larva and adults was extensively transformed in the process.

Parasitoidism, not sociality, is associated with the evolution of elaborate mushroom bodies in the brains of hymenopteran insects

The social brain hypothesis posits that the cognitive demands of social behaviour have driven evolutionary expansions in brain size in some vertebrate lineages. In insects, higher brain centres called mushroom bodies are enlarged and morphologically elaborate (having doubled, invaginated and subcompartmentalized calyces that receive visual input) in social species such as the ants, bees and wasps of the aculeate Hymenoptera, suggesting that the social brain hypothesis may also apply to invertebrate animals. In a quantitative and qualitative survey of mushroom body morphology across the Hymenoptera, we demonstrate that large, elaborate mushroom bodies arose concurrent with the acquisition of a parasitoid mode of life at the base of the Euhymenopteran (Orussioidea + Apocrita) lineage, approximately 90 Myr before the evolution of sociality in the Aculeata. Thus, sociality could not have driven mushroom body elaboration in the Hymenoptera. Rather, we propose that the cognitive demands of host-finding behaviour in parasitoids, particularly the capacity for associative and spatial learning, drove the acquisition of this evolutionarily novel mushroom body architecture. These neurobehavioural modifications may have served as pre-adaptations for central place foraging, a spatial learning-intensive behaviour that is widespread across the Aculeata and may have contributed to the multiple acquisitions of sociality in this taxon.

An expansion of the genome size dataset for the insect order Hymenoptera, with a first test of parasitism and eusociality as possible constraints

Although the Hymenoptera represent a remarkably diverse and socioeconomically important group that is of considerable interest in genome biology, they remain understudied in terms of genome size. This study reports new genome size estimates for 89 species of ants, bees and wasps, representing 17 families and four superfamilies. These are used in a test of the hypothesis that genome sizes are constrained by traits associated with parasitism or eusociality. Not all parasitoid wasps exhibit small genomes, though a relationship based on specific types of parasitism may still occur; by contrast, there was no convincing evidence of a constraint relating to eusociality. The data provided here can be used to guide future research aimed at understanding the evolution of large-scale genomic properties in this order.