Effects of ovarian fluid, venom and egg surface characteristics of Tetrastichus brontispae (Hymenoptera: Eulophidae) on the immune response of Octodonta nipae (Coleoptera: Chrysomelidae)

The Symbiotic Bacteria-Xenorhabdus nematophila All and Photorhabdus luminescens H06 Strongly Affected the Phenoloxidase Activation of Nipa Palm Hispid, Octodonta nipae (Coleoptera: Chrysomelidae) Larvae

Symbiotic bacteria form a mutualistic relationship with nematodes and are pathogenic to many insect pests. They kill insects using various strategies to evade or suppress their humoral and cellular immunity. Here we evaluate the toxic effects of these bacteria and their secondary metabolites on the survival and phenoloxidase (PO) activation of Octodonta nipae larvae using biochemical and molecular methods. The results show P. luminescens H06 and X. nematophila All treatments caused significant reductions in the number of O. nipae larvae in a dose-dependent manner. Secondly, the O. nipae immune system recognizes symbiotic bacteria at early and late stages of infection via the induction of C-type lectin. Live symbiotic bacteria significantly inhibit PO activity in O. nipae whereas heat-treated bacteria strongly increase PO activity. Additionally, expression levels of four O. nipae proPhenoloxidase genes following treatment with P. luminescens H06 and X. nematophila All were compared. We found that the expression levels of all proPhenoloxidase genes were significantly down-regulated at all-time points. Similarly, treatments of O. nipae larvae with metabolites benzylideneacetone and oxindole significantly down-regulated the expression of the PPO gene and inhibited PO activity. However, the addition of arachidonic acid to metabolite-treated larvae restored the expression level of the PPO gene and increased PO activity. Our results provide new insight into the roles of symbiotic bacteria in countering the insect phenoloxidase activation system.

The Cellular Immunological Responses and Developmental Differences between Two Hosts Parasitized by Asecodes hispinarum

This study aims to investigate the developmental interactions of Asecodes hispinarum Bouček on Brontispa longissima Gestro and Octodonta nipae Maulik, as well as the cellular immune responses of B. longissima and O. nipae larvae in response to parasitism by A. hispinarum, with the hope of determining the reason for the difference in larval breeding of A. hispinarum in B. longissima and O. nipae. The effects of parasitism by A. hispinarum on the larval development, hemocyte count, and proportion of the hemocyte composition of the two hosts were carried out through selective assay and non-selective assay using statistical analysis and anatomical imaging. There was no significant difference in parasitic selection for A. hispinarum on the larvae of these two beetles; however, more eggs were laid to B. longissima larvae than to O. nipae larvae after parasitism by A. hispinarum. The eggs of A. hispinarum were able to grow and develop normally inside the larvae of B. longissima, and the parasitism caused the larvae of B. longissima become rigid within 7 d, with a high larval mortality rate of 98.88%. In contrast, the eggs of A. hispinarum were not able to develop normally inside the O. nipae larvae, with a high encapsulation rate of 99.05%. In addition, the parasitism by A. hispinarum caused a 15.31% mortality rate in O. nipae larvae and prolonged the larval stage by 5 d and the pupal stage by 1 d. The number of hemocytes during the 12, 24, 48, 72, and 96 h of the four instars from O. nipae larvae was 6.08 times higher than from B. longissima larvae of the same age. After 24 h of being parasitized by A. hispinarum, the total number of hemocytes and granulocyte proportion of B. longissima larvae increased significantly. However, the total number of hemocytes and plasmatocyte proportion of O. nipae increased significantly after 24, 72, and 96 h, and the proportion of granulocytes increased significantly after 12 h post-parasitism. The results in the present study indicated that A. hispinarum was unable to successfully reproduce offspring in O. nipae, but its spawning behavior had an adverse effect on the larval development of its host. In addition, the adequate number of hemocytes and more pronounced changes in the hemocyte count and hemocyte composition ratio in the larvae after parasitization may be important factors for the successful encapsulation in O. nipae larvae.

An endoparasitoid uses its egg surface proteins to regulate its host immune response

With proteomic analysis, we identified 379 egg surface proteins from an endoparasitoid, Cotesia chilonis. Proteins containing conserved enzymatic domains constitute a large proportion of egg surface components. Some proteins, such as superoxidase dismutase, homolog of C. rubecula 32-kDa protein, and immunoevasive protein-2A, are classical parasitism factors that have known functions in host immunity regulation. Melanization assays revealed that a novel egg surface protein, C. chilonis egg surface serpin domain-containing protein had the same function as a C. chilonis venom serpin, as both suppressed host melanization in a dose-dependent manner. C. chilonis egg surface serpin domain-containing protein is mainly transcribed in C. chilonis oocytes with follicular cells, and it is located on both the anterior and posterior sides of the mature egg surface. Additionally, we used LC-MS/MS to identify 586 binding proteins sourced from C. suppressalis plasma located on the eggshell surface of C. chilonis, which included some immunity-related proteins. These results not only indicate that C. chilonis uses its egg surface proteins to reduce the immune response of its host but also imply that endoparasitoid egg surface proteins might be a new parasitism factor involved in host immune regulation.

The Entomopathogenic Nematodes H. bacteriophora and S. carpocapsae Inhibit the Activation of proPO System of the Nipa Palm Hispid Octodonta nipae (Coleoptera: Chrysomelidae)

Entomopathogenic nematodes are biocontrol agents of invasive insect pests in soil and cryptic habitats. Nipa palm hispid, Octodonta nipae, is a pest of palm trees in Sothern China. To address its increasing damage, environmentally friendly control methods are required. This study aimed to test efficacy of Heterorhabditis bacteriophora and Steinernema carpocapsae on O. nipae and investigated the influence of secondary metabolites, nematodes, and their isolated cuticles on the activation of O. nipae’s prophenoloxidase system using qPCR analysis. Our data revealed that O. nipae were less susceptible to H. bacteriophora than S. carpocapsae and penetrations of infective juveniles were higher with S. carpocapsae treatment than H. bacteriophora. Moreover, expression levels of the serine protease P56, prophenoloxidase activation factor 1, PPO and serine protease inhibitor 28 upon S. carpocapsae and H. bacteriophora infections were generally downregulated at all times. However, upon heating, the cuticles lost their inhibitory effects and resulted in upregulation of the PPO gene. Similarly, the addition of arachidonic acid reversed the process and resulted in the upregulation of the PPO gene compared to the control. Further work is needed to identify toxic substances secreted by these EPNs to evade O. nipae’s immune system.

Parasitism rate of Plutella xylostella (Lepidoptera: Plutellidae) larvae in greenhouse by Tetrastichus howardi (Hymenoptera: Eulophidae) females at different densities

Abstract Parasitoids control insect pests, but their number per host affects their efficiency. The objective of this work was to evaluate the best density of Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) individuals parasitizing fourth instar Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) larvae in greenhouse conditions. These larvae were exposed to parasitism by T. howardi females with 1:1, 3:1, 6:1, 9:1, 12:1, 15:1 and 18:1 parasitoid/host ratios with 10 replications during 96 hours. After this period the larvae were kept on host plants (Brassica oleracea) until pupa formation. Tetrastichus howardi parasitized and reproduced in P. xylostella larvae at all its densities tested, but with higher values, 84% and 10 ± 2.4 individuals, respectively, with 9:1 parasitoids/host. Nine T. howardi females per P. xylostella larvae are the adequate number to manage this insect pest.

Immunosuppressive influence of parasitoid wasp Pimpla turionellae calyx fluid on host Galleria mellonella cell-mediated immune response and hemocyte viability

Endoparasitoid species devoid of symbiotic viruses inject secretions derived from their reproductive glands into their hosts during parasitism in order to avoid various immune responses of their hosts. Pimpla turionellae L. (Hymenoptera: Ichneumonidae) is an endoparasitoid that lacks polydnaviruses, and its venom has previously been shown to paralyze the host Galleria mellonella (Lepidoptera: Pyralidae) and suppress its immune reactions to ensure the egg survival. The present study demonstrates that another female-injected factor calyx fluid extracted from the P. turionellae ovary is also responsible for the suppression of G. mellonella immunity. The total hemocyte counts of G. mellonella decrease after treatment with calyx fluid in a concentration-dependent manner. Significant reductions in cell viability are also observed at all calyx fluid doses both in vivo and in vitro. The analyses of the beads injected into the insects as encapsulation targets revealed that the number of encapsulated beads reduced significantly compared to controls post-calyx fluid injection. The injection of the highest calyx fluid dose (1 female equivalent calyx) is sufficient to completely inhibit the strong encapsulation and melanization reactions of the last instar larvae 24 h post-injection. These results demonstrate that P. turionellae calyx fluid is required to regulate host immunity for successful parasitization.

Variation in Parasitoid Virulence of Tetrastichus brontispae during the Targeting of Two Host Beetles

In host-parasitoid interactions, antagonistic relationship drives parasitoids to vary in virulence in facing different hosts, which makes these systems excellent models for stress-induced evolutionary studies. Venom compositions varied between two strains of Tetrastichus brontispae, Tb-Bl and Tb-On. Tb-Bl targets Brontispa longissima pupae as hosts, and Tb-On is a sub-population of Tb-Bl, which has been experimentally adapted to a new host, Octodonta nipae. Aiming to examine variation in parasitoid virulence of the two strains toward two hosts, we used reciprocal injection experiments to compare effect of venom/ovarian fluids from the two strains on cytotoxicity, inhibition of immunity and fat body lysis of the two hosts. We found that Tb-Onvenom was more virulent towards plasmatocyte spreading, granulocyte function and phenoloxidase activity than Tb-Blvenom. Tb-Blovary was able to suppress encapsulation and phagocytosis in both hosts; however, Tb-Onovary inhibition targeted only B. longissima. Our data suggest that the venom undergoes rapid evolution when facing different hosts, and that the wasp has good evolutionary plasticity.

An integrated transcriptomic and proteomic approach to identify the main Torymus sinensis venom components

During oviposition, ectoparasitoid wasps not only inject their eggs but also a complex mixture of proteins and peptides (venom) in order to regulate the host physiology to benefit their progeny. Although several endoparasitoid venom proteins have been identified, little is known about the components of ectoparasitoid venom. To characterize the protein composition of Torymus sinensis Kamijo (Hymenoptera: Torymidae) venom, we used an integrated transcriptomic and proteomic approach and identified 143 venom proteins. Moreover, focusing on venom gland transcriptome, we selected additional 52 transcripts encoding putative venom proteins. As in other parasitoid venoms, hydrolases, including proteases, phosphatases, esterases, and nucleases, constitute the most abundant families in T. sinensis venom, followed by protease inhibitors. These proteins are potentially involved in the complex parasitic syndrome, with different effects on the immune system, physiological processes and development of the host, and contribute to provide nutrients to the parasitoid progeny. Although additional in vivo studies are needed, initial findings offer important information about venom factors and their putative host effects, which are essential to ensure the success of parasitism.

Identifications, Characteristics, and Expression Patterns of Small Heat Shock Protein Genes in a Major Mulberry Pest, Glyphodes pyloalis (Lepidoptera: Pyralidae)

Six candidate sHSP genes were identified from the Glyphodes pyloalis transcriptome. All sHSP genes included full-length open reading frames and shared high similarity with the sequences of other lepidopteran species. These sHSP genes encoded 175-191 amino acid residues, and the predicted proteins had a molecular weight from 19.5 to 21.8 kDa. All GpsHSPs were expressed at lower levels at larval stages. All GpsHSPs were expressed at higher levels at diapaused, prepupal, or pupal stages, suggesting that sHSPs may be involved in metamorphosis in G. pyloalis. In addition to the developmental stage, extreme temperatures can induce variations in the expression of sHSPs genes. All GpsHSPs were significantly upregulated in larvae following exposure to heat shock, except GpHSP21.4 which downregulated at 4 h following exposure to the cold shock treatment. Furthermore, Starvation influenced the expression patterns of GpsHSPs as a function of the duration of food deprivation. Four GpsHSPs increased their expression with time of starvation until reaching to the peak level at 6 d of starvation. Finally, parasitism by the endoparasitoid Aulacocentrum confusum He et van Achterberg (Hymenoptera: Braconidae)-induced fluctuations in the expression of all GpsHSPs, and the expression varied with time after parasitization. Our results from this study strongly suggest functional differentiation within the sHSPs subfamily in G. pyloalis. The present study would provide further insight into the roles of sHSPs in G. pyloalis and novel avenues for promoting integrated management of this pest.

Cloning and Immunosuppressive Properties of an Acyl-Activating Enzyme from the Venom Apparatus of Tetrastichus brontispae (Hymenoptera: Eulophidae)

Venom injected into the host plays vital roles in facilitating successful parasitization and development for parasitoid wasps, especially those devoid of polydnavirus, and the abundant venom proteins appear to be most likely involved in parasitization success. Previously, we found the four most abundant venom proteins, including 4-coumarate:CoA ligase-like 4 (4CL4-like), in the Tetrastichus brontispae (Hymenoptera: Eulophidae) venom apparatus. In this study, we cloned, expressed T. brontispae 4CL4-like (Tb4CL4-like) in Escherichia coli, and investigated its immunosuppressive properties. The deduced amino acid sequence for Tb4CL4-like shares high identity at conserved amino acids associated with the acyl-activating enzyme (AAE) consensus motif but shows only <40% identity with the members in the AAE superfamily. mRNA abundance analysis indicated that Tb4CL4-like was transcribed mainly in the venom apparatus. Recombinant Tb4CL4-like inhibited Octodonta nipae (Coleoptera: Chrysomelidae) pupal cellular encapsulation and spreading by targeting the hemocyte cytoskeleton and reduced the hemocyte-mediated phagocytosis of E. coli in vivo. Moreover, Tb4CL4-like exhibited greater affinity to palmitic acid and linolenic acid based on the molecular docking assay and is hypothesized to be involved in fatty acid metabolism. In conclusion, our results suggest that Tb4CL4-like may be an immunity-related AAE protein that is involved in the regulation of host immunity through fatty acid metabolism-derived signaling pathways.

Exploring the Role of Relish on Antimicrobial Peptide Expressions (AMPs) Upon Nematode-Bacteria Complex Challenge in the Nipa Palm Hispid Beetle, Octodonta nipae Maulik (Coleoptera: Chrysomelidae)

The humoral immune responses of the nipa palm hispid beetle Octodonta nipae involves the inducible expression of the genes coding for antimicrobial peptides (AMPs) which are mediated by immune deficiency signaling pathways. In insects, the nuclear factor-κB (NF-κB) transcription factor, Relish, has been shown to regulate AMP gene expressions upon microbial infections. Here, we dissect the expression patterns of some AMPs in O. nipae during infections by entomopathogenic nematodes (EPNs) and their symbionts, before and after Relish knock down. Our results indicate that, prior to gene silencing, the AMPs attacin C1, attacin C2, and defensin 2B were especially expressed to great extents in the insects challenged with the nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora as well as with their respective symbionts Xenorhabdus nematophila and Photorhabdus luminescens. The study also established the partial sequence of OnRelish/NF-κB p110 subunit in O. nipae, with an open reading frame coding for a protein with 102 amino acid residues. A typical Death domain-containing protein was detected (as seen in Drosophila) at the C-terminus of the protein. Phylogenetic analysis revealed that in O. nipae, Relish is clustered with registered Relish/NF-κB p110 proteins from other species of insect especially Leptinotarsa decemlineata from the same order Coleoptera. Injection of OnRelish dsRNA remarkably brought down the expression of OnRelish and also reduced the magnitude of transcription of attacin C1 and defensin 2B upon S. carpocapsae and H. bacteriophora and their symbionts infections. Altogether, our data unveil the expression pattern of OnRelish as well as that of some AMP genes it influences during immune responses of O. nipae against EPNs and their symbionts.