Differential gene expression during wing morph differentiation of the ectoparasitoid Melittobia digitata (Hym., Eulophidae)

Identification of Venom Proteins of the Indigenous Endoparasitoid Chouioia cunea (Hymenoptera: Eulophidae)

Chouioia cunea (Yang) (Hymenoptera: Eulophidae) is an indigenous pupal endoparasitoid that effectively attacks the exotic fall webworm Hyphantria cunea (Drury) (Lepidoptera: Arctiidae) in China. In this novel association, the parasitoid's venom has played an important role in subduing the immune defense of the host although little is known about the composition and functions of the parasitoid's venom. We therefore first identified the parasitoid's major venom proteins using electrospray ionization-mass spectrometry (ESI-MS). Approximately 207 different proteins were identified from C. cunea's venom; among them 26 types widely existed in other endoparasitoids' venom, including calreticulin and arginine kinase, which inhibited the host immune system.

Identification of major Toxoneuron nigriceps venom proteins using an integrated transcriptomic/proteomic approach

Endoparasitoids in the order Hymenoptera are natural enemies of several herbivorous insect pest species. During oviposition they inject a mixture of factors, which include venom, into the host, ensuring the successful parasitism and the development of their progeny. Although these parasitoid factors are known to be responsible for host manipulation, such as immune system suppression, little is known about both identity and function of the majority of their venom components. To identify the major proteins of Toxoneuron nigriceps (Hymenoptera: Braconidae) venom, we used an integrated transcriptomic and proteomic approach. The tandem-mass spectrometric (LC-MS/MS) data combined with T. nigriceps venom gland transcriptome used as a reference database resulted in the identification of a total of thirty one different proteins. While some of the identified proteins have been described in venom from several parasitoids, others were identified for the first time. Among the identified proteins, hydrolases constituted the most abundant family followed by transferases, oxidoreductases, ligases, lyases and isomerases. The hydrolases identified in the T. nigriceps venom glands included proteases, peptidases and glycosidases, reported as common components of venom from several parasitoid species. Taken together, the identified proteins included factors that could potentially inhibit the host immune system, manipulate host physiological processes and host development, as well as provide nutrients to the parasitoid progeny, degrading host tissues by specific hydrolytic enzymes. The venom decoding provides us with information about the identity of candidate venom factors which could contribute to the success of parasitism, together with other maternal and embryonic factors.

The venom gland transcriptome of the parasitoid wasp Nasonia vitripennis highlights the importance of novel genes in venom function

Background

Prior to egg laying the parasitoid wasp Nasonia vitripennis envenomates its pupal host with a complex mixture of venom peptides. This venom induces several dramatic changes in the host, including developmental arrest, immunosuppression, and altered metabolism. The diverse and potent bioactivity of N. vitripennis venom provides opportunities for the development of novel acting pharmaceuticals based on these molecules. However, currently very little is known about the specific functions of individual venom peptides or what mechanisms underlie the hosts response to envenomation. Many of the venom peptides also lack bioinformatically derived annotations because no homologs can be identified in the sequences databases. The RNA interference system of N. vitripennis provides a method for functional characterisation of venom protein encoding genes, however working with the current list of 79 candidates represents a daunting task. For this reason we were interested in determining the expression levels of venom encoding genes in the venom gland, as this information could be used to rank candidates for further study. To do this we carried out deep transcriptome sequencing of the venom gland and ovary tissue and used RNA-seq to rank the venom protein encoding genes by expression level. The generation of a specific venom gland transcriptome dataset also provides further opportunities to investigate novel features of this specialised organ.

Results

RNA-seq revealed that the highest expressed venom encoding gene in the venom gland was ‘Venom protein Y’. The highest expressed annotated gene in this tissue was serine protease Nasvi2EG007167, which has previously been implicated in the apoptotic activity of N. vitripennis venom. As expected the RNA-seq confirmed that venom encoding genes are almost exclusively expressed in the venom gland relative to the neighbouring ovary tissue. Novel genes appear to perform key roles in N. vitripennis venom function, with over half of the 15 highest expressed venom encoding loci lacking bioinformatic annotations. The high throughput sequencing data also provided evidence for the existence of an additional 472 previously undescribed transcribed regions in the N. vitripennis genome. Finally, metatranscriptomic analysis of the venom gland transcriptome finds little evidence for the role of Wolbachia in the venom system.

Conclusions

The expression level information provided here for the N. vitripennis venom protein encoding genes represents a valuable dataset that can be used by the research community to rank candidates for further functional characterisation. These candidates represent bioactive peptides valuable in the development of new pharmaceuticals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2924-7) contains supplementary material, which is available to authorized users.

Effects of biotic and abiotic factors on phenotypic partitioning of wing morphology and development in Sclerodermus pupariae (Hymenoptera: Bethylidae)

Wing phenotype polymorphism is commonly observed in insects, yet little is known about the influence of environmental cues on the development or expression of the alternative phenotypes. Here, we report how both biotic and abiotic factors affect the wing morph differentiation of a bethylid parasitoid Sclerodermus pupariae. The percentage of winged female parasitoid progeny increased exponentially with temperature between 20 °C to 30 °C. Low intensity light and short-day photoperiod conditions also significantly induced the development of winged morphs. Interestingly, wingless maternal parasitoids produced more winged progeny. Furthermore, the degree of wing dimorphism was significantly influenced by the interactions between light intensity and maternal wing morphs. The percentage of winged female progeny was not significantly influenced by foundress densities, but increased significantly with parasitoid brood sizes. However, the percentage of male progeny increased significantly with the densities of maternal parasitoids. Our findings highlight the phenotypic partitioning of wing morphology and development in the parasitoid S. pupariae under varied environmental cues, and reveal the most favourable conditions for the production of winged females in this bethylid wasp. It is thus possible to increase winged female parasitoid production for the purposes of biological control by manipulation of biotic and abiotic conditions.

Transcriptomics and identification of the chemoreceptor superfamily of the pupal parasitoid of the oriental fruit fly, Spalangia endius Walker (Hymenoptera: Pteromalidae)

Background

The oriental fruit fly, Bactrocera dorsalis Hendel, causes serious losses to fruit production and is one of the most economically important pests in many countries, including China, Spalangia endius Walker is a pupal parasitoid of various dipteran hosts, and may be considered a potentially important ectoparasitic pupal parasitoid of B. dorsalis. However, lack of genetic information on this organism is an obstacle to understanding the mechanisms behind its interaction with this host. Analysis of the S. endius transcriptome is essential to extend the resources of genetic information on this species and, to support studies on S. endius on the host B. dorsalis.

Methodology/Principal Findings

We performed de novo assembly RNA-seq of S. endius. We obtained nearly 10 Gbp of data using a HiSeq platform, and 36319 high-quality transcripts using Trinity software. A total of 22443 (61.79%) unigenes were aligned to homologous sequences in the jewel wasp and honeybee (Apis florae) protein set from public databases. A total of 10037 protein domains were identified in 7892 S. endius transcripts using HMMER3 software. We identified expression of six gustatory receptor and 21 odorant receptor genes in the sample, with only one gene having a high expression level in each family. The other genes had a low expression level, including two genes regulated by splicing. This result may be due to the wasps being kept under laboratory conditions. Additionally, a total of 3727 SSR markers were predicted, which could facilitate the identification of polymorphisms and functional genes within wasp populations.

Conclusion/Significance

This transcriptome greatly improves our genetic understanding of S. endius and provides a large number of gene sequences for further study.

Competition between relatives and the evolution of dispersal in a parasitoid wasp

Evolutionary theory predicts that levels of dispersal vary in response to the extent of local competition for resources and the relatedness between potential competitors. Here, we test these predictions by making use of a female dispersal dimorphism in the parasitoid wasp Melittobia australica. We show that there are two distinct female morphs, which differ in morphology, pattern of egg production, and dispersal behaviour. As predicted by theory, we found that greater competition for resources resulted in increased production of dispersing females. In contrast, we did not find support for the prediction that high relatedness between competitors increases the production of dispersing females in Melittobia. Finally, we exploit the close links between the evolutionary processes leading to selection for dispersal and for biased sex ratios to examine whether the pattern of dispersal can help distinguish between competing hypotheses for the lack of sex ratio adjustment in Melittobia.

Insights into the venom composition of the ectoparasitoid wasp Nasonia vitripennis from bioinformatic and proteomic studies

With the Nasonia vitripennis genome sequences available, we attempted to determine the proteins present in venom by two different approaches. First, we searched for the transcripts of venom proteins by a bioinformatic approach using amino acid sequences of known hymenopteran venom proteins. Second, we performed proteomic analyses of crude N. vitripennis venom removed from the venom reservoir, implementing both an off-line two-dimensional liquid chromatography matrix-assisted laser desorption/ ionization time-of-flight (2D-LC-MALDI-TOF) mass spectrometry (MS) and a two-dimensional liquid chromatography electrospray ionization Founer transform ion cyclotron resonance (2D-LC-ESI-FT-ICR) MS setup. This combination of bioinformatic and proteomic studies resulted in an extraordinary richness of identified venom constituents. Moreover, half of the 79 identified proteins were not yet associated with insect venoms: 16 proteins showed similarity only to known proteins from other tissues or secretions, and an additional 23 did not show similarity to any known protein. Serine proteases and their inhibitors were the most represented. Fifteen nonsecretory proteins were also identified by proteomic means and probably represent so-called 'venom trace elements'. The present study contributes greatly to the understanding of the biological diversity of the venom of parasitoid wasps at the molecular level.

A venom metalloproteinase from the parasitic wasp Eulophus pennicornis is toxic towards its host, tomato moth (Lacanobia oleracae)

Three genes encoding clan MB metalloproteinases (EpMP1-3) were identified from venom glands of the ectoparasitic wasp Eulophus pennicornis. The derived amino acid sequences predict mature proteins of approximately 46 kDa, with a novel two-domain structure comprising a C-terminal reprolysin domain, and an N-terminal domain of unknown function. EpMP3 expressed as a recombinant protein in Pichia pastoris had gelatinase activity, which was inhibited by EDTA. Injection of recombinant EpMP3 into fifth instar Lacanobia oleracea (host) larvae resulted in partial insect mortality associated with the moult to sixth instar, with surviving insects showing retarded development and growth. EpMP3 is expressed specifically in venom glands. These results suggest that EpMP3 is a functional component of Eulophus venom, which is able to manipulate host development.

Biology of the parasitoid Melittobia (Hymenoptera: Eulophidae)

As parasitoids upon solitary bees and wasps and their nest cohabitants, Melittobia have an intricate life history that involves both female cooperation and variably expressed male siblicidal conflict. Inter- and intrasexual dimorphism includes blind, flightless males and (probably nutritionally determined) short- and long-winged females. Thought to be highly inbred, Melittobia do not conform to local mate competition (LMC) theory but exhibit simple forms of many social insect traits, including overlapping adult generations, different female phenotypes, close kinship ties, parental care, and altruistic cooperative escape behaviors. Most host records and research findings are based on only 3 species--M. acasta, M. australica, and M. digitata--but any of the 12 species could have pest potential due to their polyphagy, explosive population growth, cryptic habits, and behavioral plasticity. Readily cultured in the laboratory, Melittobia offer considerable potential as a model for genetic, developmental, and behavioral studies.