Special Issue "Insect Parasites: A Focus on Wasps and Nematodes"

A special issue of Insects (ISSN 2075-4450).

Deadline for manuscript submissions: 30 November 2020.

Special Issue Editors

Prof. Dr. Maurizio Francesco Brivio
Website SciProfiles
Guest Editor
Lab of Comparative Immunology and Parasitology University of Insubria, Varese, Italy
Interests: Insect Immunity, Innate Immunity, Parasitology, nematodes, host-parasite interaction
Prof. Patrizia Falabella
Website
Guest Editor
Lab of Insect physiology and molecular biology, University of Basilicata, Italy
Interests: Insect Immunity; molecular bases of host-parasitoid interaction; Molecular Bases of insect olfactive perception; bioconversion processes by Hermetia illucens; insects as source of Antimicrobial Peptides

Special Issue Information

Dear Colleagues,

Various organisms are used to control harmful insects with the aim of avoiding or reducing the use of pesticides. Among them, parasitic wasps and entomopathogenic nematodes are the most widely used and efficient. These species share common strategies to assure the development of the offspring inside the insect body, although they differ either in the way they enter the body of the host or in the immunoevasive and immunodepressive strategies adopted to neutralize the insect immune response. Both of these organisms have evolved complex mechanisms to elude and neutralize host immunocompetent cells and the humoral defence system. Nematodes use both body surface components and secretions, supported by secretions and components of the bacterial wall of the symbionts. The synergistic action of the nematode and its symbionts induces an immunodepression that culminates in the death of the host. The host corpse is then used to feed the offspring of the nematodes. Parasitoid wasps do not penetrate the target insect but lay their eggs inside (endoparasitoids) or outside (ectoparasitoids) the host's body. Both ecto- and endoparasitoids inject secretions of maternal origin responsible for host physiology alterations in the host body, ensuring parasitization success. In this Special Issue, we aim to collect papers outlining approaches used by wasps or nematodes to efficiently parasitize their target insects, including those that are similar and those that are not.

Prof. Maurizio Francesco Brivio
Prof. Patrizia Falabella
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Insects is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • parasites
  • insect immunity
  • nematodes
  • wasps
  • parasitoid
  • venom
  • polydnavirus

Published Papers (6 papers)

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Research

Open AccessArticle
Palaearctic Egg Parasitoids Interaction to Three Grapevine Exotic Pests in Northwestern Italy: A New Association Involving Metcalfa pruinosa
Insects 2020, 11(9), 610; https://doi.org/10.3390/insects11090610 - 08 Sep 2020
Abstract
The most important exotic leafhopper pests currently affecting the Italian vineyards are the leafhoppers Scaphoideus titanus, Orientus ishidae and the planthopper Metcalfa pruinosa. Their highest population density is detected in the uncultivated areas with wild grapevines. Should these habitats be considered [...] Read more.
The most important exotic leafhopper pests currently affecting the Italian vineyards are the leafhoppers Scaphoideus titanus, Orientus ishidae and the planthopper Metcalfa pruinosa. Their highest population density is detected in the uncultivated areas with wild grapevines. Should these habitats be considered only a problem or a potential resource for Palearctic entomophagy of these three exotic pests? The aim of this work was to study the biotopes and biocoenosis present in the Piedmontese vineyard agroecosystem, evaluating the parasitization rate and other crucial aspects for a possible application in biological control. Several specimens of egg-parasitoid wasps were obtained from filed-collected two-year-old grapevine canes. The most prevalent one belonged to the Oligosita collina group (Trichogrammatidae) emerged only from M. pruinosa eggs with a parasitization rate of over 40%. The new association is the first report of such a high level of parasitization on the flatid planthopper. The parasitization rate mainly relied on the host egg density and the abundance of plants suitable for the oviposition. A second parasitoid generation on the overwintering eggs is discussed, as well as other hypothesis. Furthermore, the parasitization rate was higher than the one showed by the dryinid Neodryinus typhlocybae, the control agent introduced in Italy under the biological control strategy, highlighting a possible implication in this biocoenosis. We assume that the egg parasitoid adaptation may contribute to M. pruinosa control. Full article
(This article belongs to the Special Issue Insect Parasites: A Focus on Wasps and Nematodes)
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Open AccessArticle
The Venom of the Ectoparasitoid Wasp Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) Induces Apoptosis of Drosophila melanogaster Hemocytes
Insects 2020, 11(6), 363; https://doi.org/10.3390/insects11060363 - 11 Jun 2020
Abstract
The pupal ectoparasitoid Pachycrepoideus vindemiae injects venom into its fly hosts prior to oviposition. We have shown that this venom causes immune suppression in Drosophila melanogaster pupa but the mechanism involved remained unclear. Here, we show using transgenic D. melanogaster with fluorescent hemocytes [...] Read more.
The pupal ectoparasitoid Pachycrepoideus vindemiae injects venom into its fly hosts prior to oviposition. We have shown that this venom causes immune suppression in Drosophila melanogaster pupa but the mechanism involved remained unclear. Here, we show using transgenic D. melanogaster with fluorescent hemocytes that the in vivo number of plasmatocytes and lamellocytes decreases after envenomation while it has a limited effect on crystal cells. After in vitro incubation with venom, the cytoskeleton of plasmatocytes underwent rearrangement with actin aggregation around the internal vacuoles, which increased with incubation time and venom concentration. The venom also decreased the lamellocytes adhesion capacity and induced nucleus fragmentation. Electron microscopy observation revealed that the shape of the nucleus and mitochondria became irregular after in vivo incubation with venom and confirmed the increased vacuolization with the formation of autophagosomes-like structures. Almost all venom-treated hemocytes became positive for TUNEL assays, indicating massive induced apoptosis. In support, the caspase inhibitor Z-VAD-FMK attenuated the venom-induced morphological changes suggesting an involvement of caspases. Our data indicate that P. vindemiae venom inhibits D. melanogaster host immunity by inducing strong apoptosis in hemocytes. These assays will help identify the individual venom component(s) responsible and the precise mechanism(s)/pathway(s) involved. Full article
(This article belongs to the Special Issue Insect Parasites: A Focus on Wasps and Nematodes)
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Open AccessArticle
Insight into the Functional Diversification of Lipases in the Endoparasitoid Pteromalus puparum (Hymenoptera: Pteromalidae) by Genome-scale Annotation and Expression Analysis
Insects 2020, 11(4), 227; https://doi.org/10.3390/insects11040227 - 05 Apr 2020
Cited by 1
Abstract
Lipases play essential roles in digestion, transport, and processing of dietary lipids in insects. For parasitoid wasps with a unique life cycle, lipase functions could be multitudinous in particular. Pteromalus puparum is a pupal endoparasitoid of butterflies. The female adult deposits eggs into [...] Read more.
Lipases play essential roles in digestion, transport, and processing of dietary lipids in insects. For parasitoid wasps with a unique life cycle, lipase functions could be multitudinous in particular. Pteromalus puparum is a pupal endoparasitoid of butterflies. The female adult deposits eggs into its host, along with multifunctional venom, and the developing larvae consume host as its main nutrition source. Parasitoid lipases are known to participate in the food digestion process, but the mechanism remains unclear. P. puparum genome and transcriptome data were interrogated. Multiple alignments and phylogenetic trees were constructed. We annotated a total of 64 predicted lipase genes belonging to five lipase families and suggested that eight venom and four salivary lipases could determine host nutrition environment post-parasitization. Many putative venom lipases were found with incomplete catalytic triads, relatively long β9 loops, and short lids. Data analysis reveals the loss of catalytic activities and weak triacylglycerol (TAG) hydrolytic activities of lipases in venom. Phylogenetic trees indicate various predicted functions of lipases in P. puparum. Our information enriches the database of parasitoid lipases and the knowledge of their functional diversification, providing novel insight into how parasitoid wasps manipulate host lipid storage by using venom lipases. Full article
(This article belongs to the Special Issue Insect Parasites: A Focus on Wasps and Nematodes)
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Open AccessArticle
Immune Response of Drosophila suzukii Larvae to Infection with the Nematobacterial Complex Steinernema carpocapsae–Xenorhabdus nematophila
Insects 2020, 11(4), 210; https://doi.org/10.3390/insects11040210 - 28 Mar 2020
Cited by 3
Abstract
Entomopathogenic nematodes have been proposed as biological agents for the control of Drosophila suzukii, an invasive pest of small-stone and soft-skinned fruits. Larvae of the fly are susceptible to Steinernema carpocapsae infection but the reaction of immune defenses of the host are [...] Read more.
Entomopathogenic nematodes have been proposed as biological agents for the control of Drosophila suzukii, an invasive pest of small-stone and soft-skinned fruits. Larvae of the fly are susceptible to Steinernema carpocapsae infection but the reaction of immune defenses of the host are unknown. To determine the immune response, larvae were infected with S. carpocapsae and Xenorhabdus nematophila to evaluate the effector mechanisms of both humoral and cellular processes. The symbiont bacteria presented an inhibitory effect on the phenoloxidase cascade with a low level of melanization. Besides, X. nematophila activated the synthesis of putative antimicrobial peptides on the hemolymph of infected larvae. However, those peptides presented a lower antimicrobial activity compared to hemolymph from larvae infected with non-symbiont bacteria. Xenorhabdus nematophila avoided also the phagocytosis response of hemocytes. During in vitro and in vivo assays, S. carpocapsae was not encapsulated by cells, unless the cuticle was damaged with a lipase-treatment. Hemocyte counts confirmed differentiation of lamellocytes in the early phase of infection despite the unrecognition of the nematodes. Both X. nematophila and S. carpocapsae avoided the cellular defenses of D. suzukii larvae and depressed the humoral response. These results confirmed the potential of entomopathogenic nematodes to control D. suzukii. Full article
(This article belongs to the Special Issue Insect Parasites: A Focus on Wasps and Nematodes)
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Open AccessArticle
Functional Characterization of a Venom Protein Calreticulin in the Ectoparasitoid Pachycrepoideus vindemiae
Insects 2020, 11(1), 29; https://doi.org/10.3390/insects11010029 - 31 Dec 2019
Cited by 2
Abstract
Venom proteins act in the immunological interactions between parasitoids and their host insects. The effect of venom proteins on host immunity is not fully understood in pupal parasitoids. We identified the functions of a venom protein, calreticulin (PvCRT), in the pupal ectoparasitoid Pachycrepoideus [...] Read more.
Venom proteins act in the immunological interactions between parasitoids and their host insects. The effect of venom proteins on host immunity is not fully understood in pupal parasitoids. We identified the functions of a venom protein, calreticulin (PvCRT), in the pupal ectoparasitoid Pachycrepoideus vindemiae. Here, we report that PvCRT features a signal peptide and two conserved “calreticulin” domains. Multiple sequence alignments show that PvCRT shares 83.54% amino acid identity with CRT from both Pteromalus puparum and Nasonia vitripennis, which infers a close relationship among these three species. Using qPCR analysis, we found a lower expression level of PvCRT (0.27-fold) in the venom apparatus compared to the corresponding carcass. Immunohistochemical localization revealed that PvCRT was ubiquitously expressed in venom gland. The expression of the PvCRT gene in Drosophila transgenic lines via the UAS/Gal4 binary expression system reduced the self-encapsulation phenotype of tu(1)Sz1 mutants. Additionally, studies on humoral immunity indicate that PvCRT does not affect the antimicrobial immune responses of the host. This work on an ectoparasitoid will increase our understanding of venom–mediated host-parasitoid interactions. Full article
(This article belongs to the Special Issue Insect Parasites: A Focus on Wasps and Nematodes)
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Open AccessArticle
Identification and Expression Profiling of Peripheral Olfactory Genes in the Parasitoid Wasp Aphidius ervi (Hymenoptera: Braconidae) Reared on Different Aphid Hosts
Insects 2019, 10(11), 397; https://doi.org/10.3390/insects10110397 - 08 Nov 2019
Abstract
Generalist parasitoids of aphids, such as the wasp Aphidius ervi, display significant differences in terms of host preference and host acceptance, depending on the host on which they developed (natal host), which is preferred over a non-natal host, a trait known as [...] Read more.
Generalist parasitoids of aphids, such as the wasp Aphidius ervi, display significant differences in terms of host preference and host acceptance, depending on the host on which they developed (natal host), which is preferred over a non-natal host, a trait known as host fidelity. This trait allows females to quickly find hosts in heterogeneous environments, a process mediated by chemosensory/olfactory mechanisms, as parasitoids rely on olfaction and chemical cues during host selection. Thus, it is expected that proteins participating in chemosensory recognition, such as odorant-binding proteins (OBPs) and odorant receptors (ORs) would play a key role in host preference. In this study, we addressed the effect of parasitoid reciprocal host switching between two aphid hosts (Sitobion avenae and Acyrthosiphon pisum) on the expression patterns of chemosensory genes in the wasp A. ervi. First, by using a transcriptomic approach based on RNAseq of A. ervi females reared on S. avenae and A. pisum, we were able to annotate a total of 91 transcripts related to chemoperception. We also performed an in-silico expression analysis and found three OBPs and five ORs displaying different expression levels. Then, by using qRT-PCR amplification, we found significant differences in the expression levels of these eight genes when the parasitoids were reciprocally transplanted from S. avenae onto A. pisum and vice versa. This suggests that the expression levels of genes coding for odorant receptors and odorant-binding proteins would be regulated by the specific plant–aphid host complex where the parasitoids develop (maternal previous experience) and that chemosensory genes coding for olfactory mechanisms would play a crucial role on host preference and host acceptance, ultimately leading to the establishment of host fidelity in A. ervi parasitoids. Full article
(This article belongs to the Special Issue Insect Parasites: A Focus on Wasps and Nematodes)
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