Special Issue "Insect Pathology"

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

Deadline for manuscript submissions: closed (15 May 2013)

Special Issue Editor

Guest Editor
Prof. Dr. Drion G. Boucias

Entomology and Nematology Department, University of Florida, Building 970, Natural Area Dr. (Steinmetz Hall), Gainesville, FL 32611, USA
Website | E-Mail
Interests: insect pathology; insect disease interactions; microbial metabolites; epizootiology; microbial control; structure-function relationships; symbiont/pathogen interactions

Special Issue Information

Dear Colleagues,

Insect Pathology is a broad topic that encompasses multiple disciplines that covers the biology of microbes that have a detrimental impact on the insect fitness. Over the past decades, progress has been made in elucidating .the mechanisms responsible for the ability of microbes (viruses, bacteria, fungi, protists, algae, nematodes) to infect and replicate within the insect host. Using a combination of histological and molecular approaches specific pathogenic determinants have been identified that dictate the infectivity, virulence, and specificity of various disease-causing agents. Fundamental studies on these insect-associated microbes have provided both products and strategies used in the management of insect pest populations. In this issue a combination of original articles and minireviews, written by insect microbiologists and entomologists, will address the properties that allow entomopathogens to recognize the insect host, to gain ingress through insect defense barriers, to replicate within the host, to egress from the host, and to persist and be transmitted to healthy conspecifics.

Prof. Dr. Drion G. Boucias
Guest Editor

Submission

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. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as 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 refereed through a 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 quarterly 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 500 CHF (Swiss Francs). English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

Keywords

  • insect pathology
  • insect-disease interactions
  • pathogenic determinants
  • insecticidal toxins
  • epizootiology
  • insect defenses

Published Papers (17 papers)

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Research

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Open AccessArticle Compatibility of Isaria fumosorosea (Hypocreales: Cordycipitaceae) Blastospores with Agricultural Chemicals Used for Management of the Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae)
Insects 2013, 4(4), 694-711; doi:10.3390/insects4040694
Received: 22 August 2013 / Revised: 17 October 2013 / Accepted: 1 November 2013 / Published: 26 November 2013
Cited by 5 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text
Abstract
Biorational insecticides are being increasingly emphasized for inclusion in integrated pest management programs for invasive insects. The entomopathogenic fungus, Isaria fumosorosea, can be used to help manage the Asian citrus psyllid with minimal impact on beneficial arthropods, but its effectiveness may be
[...] Read more.
Biorational insecticides are being increasingly emphasized for inclusion in integrated pest management programs for invasive insects. The entomopathogenic fungus, Isaria fumosorosea, can be used to help manage the Asian citrus psyllid with minimal impact on beneficial arthropods, but its effectiveness may be compromised by agrochemicals used to control concurrent arthropod pests and diseases. We evaluated the compatibility of I. fumosorosea blastospores with a range of spray oils and copper-based fungicides registered for use in citrus groves. Results of laboratory and greenhouse tests showed a range of responses of the fungus to the different materials, including compatibility and incompatibility. Overall, I. fumosorosea growth in vitro was reduced least by petroleum-based materials and most by botanical oils and borax, and some of the copper-based fungicides, suggesting that tank mixing of I. fumosorosea with these latter products should be avoided. However, equivalent negative effects of test materials on fungal pathogenicity were not always observed in tests with adult psyllids. We hypothesize that some oils enhanced adherence of blastospores to the insect cuticle, overcoming negative impacts on germination. Our data show that care should be taken in selecting appropriate agrochemicals for tank-mixing with commercial formulations of entomopathogenic fungi for management of citrus pests. The prospects of using I. fumosorosea for managing the invasive Asian citrus psyllid and other citrus pests are discussed. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessArticle Functional Immunomics of the Squash Bug, Anasa tristis (De Geer) (Heteroptera: Coreidae)
Insects 2013, 4(4), 712-730; doi:10.3390/insects4040712
Received: 15 September 2013 / Revised: 7 November 2013 / Accepted: 13 November 2013 / Published: 26 November 2013
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Abstract
The Squash bug, Anasa tristis (De Geer), is a major piercing/sucking pest of cucurbits, causing extensive damage to plants and fruits, and transmitting phytopathogens. No genomic resources to facilitate field and laboratory studies of this pest were available; therefore the first de novo
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The Squash bug, Anasa tristis (De Geer), is a major piercing/sucking pest of cucurbits, causing extensive damage to plants and fruits, and transmitting phytopathogens. No genomic resources to facilitate field and laboratory studies of this pest were available; therefore the first de novo exome for this destructive pest was assembled. RNA was extracted from insects challenged with bacterial and fungal immunoelicitors, insects fed on different cucurbit species, and insects from all life stages from egg to adult. All treatments and replicates were separately barcoded for subsequent analyses, then pooled for sequencing in a single lane using the Illumina HiSeq2000 platform. Over 211 million 100-base tags generated in this manner were trimmed, filtered, and cleaned, then assembled into a de novo reference transcriptome using the Broad Institute Trinity assembly algorithm. The assembly was annotated using NCBIx NR, BLAST2GO, KEGG and other databases. Of the >130,000 total assemblies 37,327 were annotated identifying the sequences of candidate gene silencing targets from immune, endocrine, reproductive, cuticle, and other physiological systems. Expression profiling of the adult immune response was accomplished by aligning the 100-base tags from each biological replicate from each treatment and controls to the annotated reference assembly of the A. tristis transcriptome. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessArticle Entomopathogenic Fungi Associated with Exotic Invasive Insect Pests in Northeastern Forests of the USA
Insects 2013, 4(4), 631-645; doi:10.3390/insects4040631
Received: 28 August 2013 / Revised: 16 October 2013 / Accepted: 23 October 2013 / Published: 4 November 2013
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Abstract
Mycopathogens of economically important exotic invasive insects in forests of northeastern USA have been the subject of research at the Entomology Research Laboratory, University of Vermont, for the last 20 years. Elongate hemlock scale, European fruit lecanium, hemlock woolly adelgid and pear thrips
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Mycopathogens of economically important exotic invasive insects in forests of northeastern USA have been the subject of research at the Entomology Research Laboratory, University of Vermont, for the last 20 years. Elongate hemlock scale, European fruit lecanium, hemlock woolly adelgid and pear thrips were analyzed for the presence of mycopathogens, in order to consider the potential for managing these pests with biological control. Fungal cultures isolated from insects with signs of fungal infection were identified based on morphological characters and DNA profiling. Mycopathogens recovered from infected insects were subdivided into three groups, i.e., specialized entomopathogenic; facultative entomopathogens; ubiquitous opportunistic contaminants. Epizootics were caused by fungi in the specialized group with the exception of M. microspora, P. marquandii and I. farinosa. Inoculation of insects in laboratory and field conditions with B. bassiana, L. muscarium and Myriangium sp. caused insect mortality of 45 to 95%. Although pest populations in the field seemed severely compromised after treatment, the remnant populations re-established themselves after the winter. Although capable of inducing high mortality, a single localized aerial application of a soil-dwelling fungus does not maintain long-time suppression of pests. However, it can halt their range expansion and maintain populations below the economic threshold level without the use of expensive insecticides which have a negative impact on the environment. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessArticle Gut Transcription in Helicoverpa zea is Dynamically Altered in Response to Baculovirus Infection
Insects 2013, 4(3), 506-520; doi:10.3390/insects4030506
Received: 15 July 2013 / Revised: 4 September 2013 / Accepted: 16 September 2013 / Published: 23 September 2013
Cited by 1 | PDF Full-text (220 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The Helicoverpa zea transcriptome was analyzed 24 h after H. zea larvae fed on artificial diet laced with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV). Significant differential regulation of 1,139 putative genes (p < 0.05 T-test with Benjamini and Hochberg False Discovery Rate) was
[...] Read more.
The Helicoverpa zea transcriptome was analyzed 24 h after H. zea larvae fed on artificial diet laced with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV). Significant differential regulation of 1,139 putative genes (p < 0.05 T-test with Benjamini and Hochberg False Discovery Rate) was detected in the gut epithelial tissue; where 63% of these genes were down-regulated and 37% of genes were up-regulated compared to the mock-infected control. Genes that play important roles in digestive physiology were noted as being generally down-regulated. Among these were aminopeptidases, trypsin-like serine proteases, lipases, esterases and serine proteases. Genes related to the immune response reacted in a complex nature having peptidoglycan binding and viral antigen recognition proteins and antiviral pathway systems down-regulated, whereas antimicrobial peptides and prophenoloxidase were up-regulated. In general, detoxification genes, specifically cytochrome P450 and glutathione S-transferase were down-regulated as a result of infection. This report offers the first comparative transcriptomic study of H. zea compared to HzSNPV infected H. zea and provides further groundwork that will lead to a larger understanding of transcriptional perturbations associated with viral infection and the host response to the viral insult in what is likely the most heavily infected tissue in the insect. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessArticle Genetic Factors and Host Traits Predict Spore Morphology for a Butterfly Pathogen
Insects 2013, 4(3), 447-462; doi:10.3390/insects4030447
Received: 15 May 2013 / Revised: 14 August 2013 / Accepted: 15 August 2013 / Published: 28 August 2013
Cited by 2 | PDF Full-text (510 KB) | HTML Full-text | XML Full-text
Abstract
Monarch butterflies (Danaus plexippus) throughout the world are commonly infected by the specialist pathogen Ophryocystis elektroscirrha (OE). This protozoan is transmitted when larvae ingest infectious stages (spores) scattered onto host plant leaves by infected adults. Parasites replicate internally during
[...] Read more.
Monarch butterflies (Danaus plexippus) throughout the world are commonly infected by the specialist pathogen Ophryocystis elektroscirrha (OE). This protozoan is transmitted when larvae ingest infectious stages (spores) scattered onto host plant leaves by infected adults. Parasites replicate internally during larval and pupal stages, and adult monarchs emerge covered with millions of dormant spores on the outsides of their bodies. Across multiple monarch populations, OE varies in prevalence and virulence. Here, we examined geographic and genetic variation in OE spore morphology using clonal parasite lineages derived from each of four host populations (eastern and western North America, South Florida and Hawaii). Spores were harvested from experimentally inoculated, captive-reared adult monarchs. Using light microscopy and digital image analysis, we measured the size, shape and color of 30 replicate spores per host. Analyses examined predictors of spore morphology, including parasite source population and clone, parasite load, and the following host traits: family line, sex, wing area, and wing color (orange and black pigmentation). Results showed significant differences in spore size and shape among parasite clones, suggesting genetic determinants of morphological variation. Spore size also increased with monarch wing size, and monarchs with larger and darker orange wings tended to have darker colored spores, consistent with the idea that parasite development depends on variation in host quality and resources. We found no evidence for effects of source population on variation in spore morphology. Collectively, these results provide support for heritable variation in spore morphology and a role for host traits in affecting parasite development. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessArticle A Third Way for Entomophthoralean Fungi to Survive the Winter: Slow Disease Transmission between Individuals of the Hibernating Host
Insects 2013, 4(3), 392-403; doi:10.3390/insects4030392
Received: 10 June 2013 / Revised: 4 July 2013 / Accepted: 9 July 2013 / Published: 23 July 2013
Cited by 1 | PDF Full-text (397 KB) | HTML Full-text | XML Full-text
Abstract
In temperate regions, insect pathogenic fungi face the challenge of surviving through the winter. Winter is a time when hosts are immobile, low in number or are present in a stage which is not susceptible to infection. Fungi from Entomophthoromycota have so far
[...] Read more.
In temperate regions, insect pathogenic fungi face the challenge of surviving through the winter. Winter is a time when hosts are immobile, low in number or are present in a stage which is not susceptible to infection. Fungi from Entomophthoromycota have so far been known to survive the winter in two ways: either as (1) thick-walled resting spores released into environment from dead hosts, or as (2) structures inside the dead host (e.g., hyphal bodies). Here we report, from the Danish environment, a third way to survive the winter, namely a slow progression and transmission of Entomophthora schizophorae in adult dipteran Pollenia hosts that hibernate in clusters in unheated attics, sheltered areas outdoors (under bark etc.). Fungus-killed sporulating flies were observed outside very early and very late in the season. By sampling adults at the time of their emergence from hibernation in late winter/early spring we documented that the fungus was naturally prevalent and killed flies after a period of incubation. Experimentally we documented that even at the low temperature of 5 °C, the fungus was able to maintain itself in Pollenia cohorts for up to 90 days. From these observations the full winter cycle of this fungus is elucidated. The three types of winter survival are discussed in relation to fungus epidemic development. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessArticle Horizontal Transmission of Metarhizium anisopliae in Fruit Flies and Effect of Fungal Infection on Egg Laying and Fertility
Insects 2013, 4(2), 206-216; doi:10.3390/insects4020206
Received: 28 March 2013 / Revised: 27 April 2013 / Accepted: 2 May 2013 / Published: 29 May 2013
Cited by 5 | PDF Full-text (163 KB) | HTML Full-text | XML Full-text
Abstract
Fly-to-fly transmission of conidia of the entomopathogenic fungus Metarhizium anisopliae and the effect of fungal infection on the reproductive potential of females surviving infection were investigated in three fruit fly species, Ceratitis cosyra, C. fasciventris, and C. capitata. The number
[...] Read more.
Fly-to-fly transmission of conidia of the entomopathogenic fungus Metarhizium anisopliae and the effect of fungal infection on the reproductive potential of females surviving infection were investigated in three fruit fly species, Ceratitis cosyra, C. fasciventris, and C. capitata. The number of conidia picked up by a single fruit fly was determined in C. cosyra. The initial uptake (Day 0) of conidia by a single fly was approx. 1.1 × 106 conidia after exposure to the treated substrate. However, the number of conidia dropped from 7.2 × 105 to 4.1 × 105 conidia after 2 and 8 h post-exposure, respectively. The number of conidia picked up by a single fungus-treated fly (“donor”) varied between 3.8 × 105 and 1.0 × 106 in the three fruit fly species, resulting in 100% mortality 5–6 days post-exposure. When fungus-free flies of both sexes (“recipient” flies) were allowed to mate with “donor” flies, the number of conidia picked up by a single fly varied between 1.0 × 105 and 2.5 × 105, resulting in a mortality of 83–100% in C. capitata, 72–85% in C. cosyra and 71–93% in C. fasciventris 10–15 days post-inoculation. There was an effect of fungal infection on female egg laying in the three species of fruit flies as control flies laid more eggs than fungus-treated females. The percentage reduction in fecundity in flies infected with M. anisopliae was 82, 73 and 37% in C. capitata, C. fasciventris and C. cosyra, respectively. The results are discussed with regard to application in autodissemination techniques. Full article
(This article belongs to the Special Issue Insect Pathology)
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Review

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Open AccessReview Bacillus thuringiensis Is an Environmental Pathogen and Host-Specificity Has Developed as an Adaptation to Human-Generated Ecological Niches
Insects 2014, 5(1), 62-91; doi:10.3390/insects5010062
Received: 18 November 2013 / Revised: 3 December 2013 / Accepted: 13 December 2013 / Published: 24 December 2013
Cited by 6 | PDF Full-text (504 KB) | HTML Full-text | XML Full-text
Abstract
Bacillus thuringiensis (Bt) has been used successfully as a biopesticide for more than 60 years. More recently, genes encoding their toxins have been used to transform plants and other organisms. Despite the large amount of research on this bacterium, its true
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Bacillus thuringiensis (Bt) has been used successfully as a biopesticide for more than 60 years. More recently, genes encoding their toxins have been used to transform plants and other organisms. Despite the large amount of research on this bacterium, its true ecology is still a matter of debate, with two major viewpoints dominating: while some understand Bt as an insect pathogen, others see it as a saprophytic bacteria from soil. In this context, Bt’s pathogenicity to other taxa and the possibility that insects may not be the primary targets of Bt are also ideas that further complicate this scenario. The existence of conflicting research results, the difficulty in developing broader ecological and genetics studies, and the great genetic plasticity of this species has cluttered a definitive concept. In this review, we gathered information on the aspects of Bt ecology that are often ignored, in the attempt to clarify the lifestyle, mechanisms of transmission and target host range of this bacterial species. As a result, we propose an integrated view to account for Bt ecology. Although Bt is indeed a pathogenic bacterium that possesses a broad arsenal for virulence and defense mechanisms, as well as a wide range of target hosts, this seems to be an adaptation to specific ecological changes acting on a versatile and cosmopolitan environmental bacterium. Bt pathogenicity and host-specificity was favored evolutionarily by increased populations of certain insect species (or other host animals), whose availability for colonization were mostly caused by anthropogenic activities. These have generated the conditions for ecological imbalances that favored dominance of specific populations of insects, arachnids, nematodes, etc., in certain areas, with narrower genetic backgrounds. These conditions provided the selective pressure for development of new hosts for pathogenic interactions, and so, host specificity of certain strains. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessReview Grooming Behavior as a Mechanism of Insect Disease Defense
Insects 2013, 4(4), 609-630; doi:10.3390/insects4040609
Received: 26 July 2013 / Revised: 20 October 2013 / Accepted: 22 October 2013 / Published: 4 November 2013
Cited by 10 | PDF Full-text (358 KB) | HTML Full-text | XML Full-text
Abstract
Grooming is a well-recognized, multipurpose, behavior in arthropods and vertebrates. In this paper, we review the literature to highlight the physical function, neurophysiological mechanisms, and role that grooming plays in insect defense against pathogenic infection. The intricate relationships between the physical, neurological and
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Grooming is a well-recognized, multipurpose, behavior in arthropods and vertebrates. In this paper, we review the literature to highlight the physical function, neurophysiological mechanisms, and role that grooming plays in insect defense against pathogenic infection. The intricate relationships between the physical, neurological and immunological mechanisms of grooming are discussed to illustrate the importance of this behavior when examining the ecology of insect-pathogen interactions. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessReview Brevibacillus laterosporus, a Pathogen of Invertebrates and a Broad-Spectrum Antimicrobial Species
Insects 2013, 4(3), 476-492; doi:10.3390/insects4030476
Received: 18 August 2013 / Revised: 30 August 2013 / Accepted: 30 August 2013 / Published: 5 September 2013
Cited by 9 | PDF Full-text (356 KB) | HTML Full-text | XML Full-text
Abstract
Brevibacillus laterosporus, a bacterium characterized by the production of a unique canoe-shaped lamellar body attached to one side of the spore, is a natural inhabitant of water, soil and insects. Its biopesticidal potential has been reported against insects in different orders including
[...] Read more.
Brevibacillus laterosporus, a bacterium characterized by the production of a unique canoe-shaped lamellar body attached to one side of the spore, is a natural inhabitant of water, soil and insects. Its biopesticidal potential has been reported against insects in different orders including Coleoptera, Lepidoptera, Diptera and against nematodes and mollusks. In addition to its pathogenicity against invertebrates, different B. laterosporus strains show a broad-spectrum antimicrobial activity including activity against phytopathogenic bacteria and fungi. A wide variety of molecules, including proteins and antibiotics, have been associated with the observed pathogenicity and mode of action. Before being considered as a biological control agent against plant pathogens, the antifungal and antibacterial properties of certain B. laterosporus strains have found medical interest, associated with the production of antibiotics with therapeutic effects. The recent whole genome sequencing of this species revealed its potential to produce polyketides, nonribosomal peptides, and toxins. Another field of growing interest is the use of this bacterium for bioremediation of contaminated sites by exploiting its biodegradation properties. The aim of the present review is to gather and discuss all recent findings on this emerging entomopathogen, giving a wider picture of its complex and broad-spectrum biocontrol activity. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessReview Occurrence and Prevalence of Insect Pathogens in Populations of the Codling Moth, Cydia pomonella L.: A Long-Term Diagnostic Survey
Insects 2013, 4(3), 425-446; doi:10.3390/insects4030425
Received: 14 May 2013 / Revised: 15 July 2013 / Accepted: 16 July 2013 / Published: 2 August 2013
Cited by 1 | PDF Full-text (450 KB) | HTML Full-text | XML Full-text
Abstract
About 20,550 larvae, pupae and adults of the codling moth, Cydia pomonella L., were diagnosed for pathogens during long-term investigations (1955–2012) at the Institute for Biological Control in Darmstadt, Germany. The prevailing entomopathogens diagnosed in these studies were insect pathogenic fungi, especially Beauveria
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About 20,550 larvae, pupae and adults of the codling moth, Cydia pomonella L., were diagnosed for pathogens during long-term investigations (1955–2012) at the Institute for Biological Control in Darmstadt, Germany. The prevailing entomopathogens diagnosed in these studies were insect pathogenic fungi, especially Beauveria bassiana and Isaria farinosa, the microsporidium, Nosema carpocapsae, the Cydia pomonella granulovirus (CpGV), as well as mostly undetermined bacteria. While the CpGV was observed exclusively in larvae and pupae from laboratory colonies or from field experiments with this virus, entomopathogenic fungi were most frequently diagnosed in last instars in autumn and in diapausing larvae and pupae in spring. B. bassiana was identified as the major fungal pathogen, causing larval prevalences of 0.9% to 100% (mean, about 32%). During prognostic long-term studies in larvae and adults of C. pomonella, N. carpocapsae was diagnosed in codling moth populations from various locations in Germany. The mean prevalence generally ranged between 20% and 50%. Experiments revealed that the fecundity and fertility of microsporidia-infected female adults were significantly reduced compared to healthy ones. The results underpin the importance of naturally occurring microbial antagonists and represent a base for further ecological studies on developing new or additional biological and integrated control strategies. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessReview Insects as a Nitrogen Source for Plants
Insects 2013, 4(3), 413-424; doi:10.3390/insects4030413
Received: 3 May 2013 / Revised: 18 June 2013 / Accepted: 9 July 2013 / Published: 31 July 2013
Cited by 1 | PDF Full-text (194 KB) | HTML Full-text | XML Full-text
Abstract
Many plants have evolved adaptations in order to survive in low nitrogen environments. One of the best-known adaptations is that of plant symbiosis with nitrogen-fixing bacteria; this is the major route by which nitrogen is incorporated into plant biomass. A portion of this
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Many plants have evolved adaptations in order to survive in low nitrogen environments. One of the best-known adaptations is that of plant symbiosis with nitrogen-fixing bacteria; this is the major route by which nitrogen is incorporated into plant biomass. A portion of this plant-associated nitrogen is then lost to insects through herbivory, and insects represent a nitrogen reservoir that is generally overlooked in nitrogen cycles. In this review we show three specialized plant adaptations that allow for the recovery of insect nitrogen; that is, plants gaining nitrogen from insects. First, we show specialized adaptations by carnivorous plants in low nitrogen habitats. Insect carnivorous plants such as pitcher plants and sundews (Nepenthaceae/Sarraceniaceae and Drosera respectively) are able to obtain substantial amounts of nitrogen from the insects that they capture. Secondly, numerous plants form associations with mycorrhizal fungi that can provide soluble nitrogen from the soil, some of which may be insect-derived nitrogen, obtained from decaying insects or insect frass. Finally, a specialized group of endophytic, insect-pathogenic fungi (EIPF) provide host plants with insect-derived nitrogen. These soil-inhabiting fungi form a remarkable symbiosis with certain plant species. They can infect a wide range of insect hosts and also form endophytic associations in which they transfer insect-derived nitrogen to the plant. Root colonizing fungi are found in disparate fungal phylogenetic lineages, indicating possible convergent evolutionary strategies between taxa, evolution potentially driven by access to carbon-containing root exudates. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessReview The Non-Photosynthetic Algae Helicosporidium spp.: Emergence of a Novel Group of Insect Pathogens
Insects 2013, 4(3), 375-391; doi:10.3390/insects4030375
Received: 30 May 2013 / Revised: 4 July 2013 / Accepted: 8 July 2013 / Published: 17 July 2013
Cited by 5 | PDF Full-text (413 KB) | HTML Full-text | XML Full-text
Abstract
Since the original description of Helicosporidium parasiticum in 1921, members of the genus Helicosporidium have been reported to infect a wide variety of invertebrates, but their characterization has remained dependent on occasional reports of infection. Recently, several new Helicosporidium isolates have been successfully
[...] Read more.
Since the original description of Helicosporidium parasiticum in 1921, members of the genus Helicosporidium have been reported to infect a wide variety of invertebrates, but their characterization has remained dependent on occasional reports of infection. Recently, several new Helicosporidium isolates have been successfully maintained in axenic cultures. The ability to produce large quantity of biological material has led to very significant advances in the understanding of Helicosporidium biology and its interactions with insect hosts. In particular, the unique infectious process has been well documented; the highly characteristic cyst and its included filamentous cell have been shown to play a central role during host infection and have been the focus of detailed morphological and developmental studies. In addition, phylogenetic analyses inferred from a multitude of molecular sequences have demonstrated that Helicosporidium are highly specialized non-photosynthetic algae (Chlorophyta: Trebouxiophyceae), and represent the first described entomopathogenic algae. This review provides an overview of (i) the morphology of Helicosporidium cell types, (ii) the Helicosporidium life cycle, including the entire infectious sequence and its impact on insect hosts, (iii) the phylogenetic analyses that have prompted the taxonomic classification of Helicosporidium as green algae, and (iv) the documented host range for this novel group of entomopathogens. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessReview Action on the Surface: Entomopathogenic Fungi versus the Insect Cuticle
Insects 2013, 4(3), 357-374; doi:10.3390/insects4030357
Received: 24 May 2013 / Revised: 3 July 2013 / Accepted: 5 July 2013 / Published: 16 July 2013
Cited by 58 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text
Abstract
Infections mediated by broad host range entomopathogenic fungi represent seminal observations that led to one of the first germ theories of disease and are a classic example of a co-evolutionary arms race between a pathogen and target hosts. These fungi are able to
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Infections mediated by broad host range entomopathogenic fungi represent seminal observations that led to one of the first germ theories of disease and are a classic example of a co-evolutionary arms race between a pathogen and target hosts. These fungi are able to parasitize susceptible hosts via direct penetration of the cuticle with the initial and potentially determining interaction occurring between the fungal spore and the insect epicuticle. Entomogenous fungi have evolved mechanisms for adhesion and recognition of host surface cues that help direct an adaptive response that includes the production of: (a) hydrolytic, assimilatory, and/or detoxifying enzymes including lipase/esterases, catalases, cytochrome P450s, proteases, and chitinases; (b) specialized infectious structures, e.g., appressoria or penetrant tubes; and (c) secondary and other metabolites that facilitate infection. Aside from immune responses, insects have evolved a number of mechanisms to keep pathogens at bay that include: (a) the production of (epi) cuticular antimicrobial lipids, proteins, and metabolites; (b) shedding of the cuticle during development; and (c) behavioral-environmental adaptations such as induced fever, burrowing, and grooming, as well as potentially enlisting the help of other microbes, all intended to stop the pathogen before it can breach the cuticle. Virulence and host-defense can be considered to be under constant reciprocal selective pressure, and the action on the surface likely contributes to phenomena such as strain variation, host range, and the increased virulence often noted once a (low) virulent strain is “passaged” through an insect host. Since the cuticle represents the first point of contact and barrier between the fungus and the insect, the “action on the surface” may represent the defining interactions that ultimately can lead either to successful mycosis by the pathogen or successful defense by the host. Knowledge concerning the molecular mechanisms underlying this interaction can shed light on the ecology and evolution of virulence and can be used for rational design strategies at increasing the effectiveness of entomopathogenic fungi for pest control in field applications. Full article
(This article belongs to the Special Issue Insect Pathology)
Open AccessReview Hirsutellin A: A Paradigmatic Example of the Insecticidal Function of Fungal Ribotoxins
Insects 2013, 4(3), 339-356; doi:10.3390/insects4030339
Received: 8 May 2013 / Revised: 21 June 2013 / Accepted: 24 June 2013 / Published: 9 July 2013
Cited by 4 | PDF Full-text (1409 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The fungal pathogen Hirsutella thompsonii produces an insecticidal protein named hirsutellin A (HtA), which has been described to be toxic to several species of mites, insect larvae, and cells. On the other hand, on the basis of an extensive biochemical and structural characterization,
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The fungal pathogen Hirsutella thompsonii produces an insecticidal protein named hirsutellin A (HtA), which has been described to be toxic to several species of mites, insect larvae, and cells. On the other hand, on the basis of an extensive biochemical and structural characterization, HtA has been considered to be a member of the ribotoxins family. Ribotoxins are fungal extracellular ribonucleases, which inactivate ribosomes by specifically cleaving a single phosphodiester bond located at the large rRNA. Although ribotoxins were brought to light in the 1960s as antitumor agents, their biological function has remained elusive. Thus, the consideration of hirsutellin A, an insecticidal protein, as a singular ribotoxin recalled the idea of the biological activity of these toxins as insecticidal agents. Further studies have demonstrated that the most representative member of the ribotoxin family, α-sarcin, also shows strong toxic action against insect cells. The determination of high resolution structures, the characterization of a large number of mutants, and the toxicity assays against different cell lines have been the tools used for the study of the mechanism of action of ribotoxins at the molecular level. The aim of this review is to serve as a compilation of the facts that allow identification of HtA as a paradigmatic example of the insecticidal function of fungal ribotoxins. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessReview Virology, Epidemiology and Pathology of Glossina Hytrosavirus, and Its Control Prospects in Laboratory Colonies of the Tsetse Fly, Glossina pallidipes (Diptera; Glossinidae)
Insects 2013, 4(3), 287-319; doi:10.3390/insects4030287
Received: 6 May 2013 / Revised: 13 June 2013 / Accepted: 13 June 2013 / Published: 2 July 2013
Cited by 4 | PDF Full-text (717 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The Glossina hytrosavirus (family Hytrosaviridae) is a double-stranded DNA virus with rod-shaped, enveloped virions. Its 190 kbp genome encodes 160 putative open reading frames. The virus replicates in the nucleus, and acquires a fragile envelope in the cell cytoplasm. Glossina hytrosavirus was
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The Glossina hytrosavirus (family Hytrosaviridae) is a double-stranded DNA virus with rod-shaped, enveloped virions. Its 190 kbp genome encodes 160 putative open reading frames. The virus replicates in the nucleus, and acquires a fragile envelope in the cell cytoplasm. Glossina hytrosavirus was first isolated from hypertrophied salivary glands of the tsetse fly, Glossina pallidipes Austen (Diptera; Glossinidae) collected in Kenya in 1986. A certain proportion of laboratory G. pallidipes flies infected by Glossina hytrosavirus develop hypertrophied salivary glands and midgut epithelial cells, gonadal anomalies and distorted sex-ratios associated with reduced insemination rates, fecundity and lifespan. These symptoms are rare in wild tsetse populations. In East Africa, G. pallidipes is one of the most important vectors of African trypanosomosis, a debilitating zoonotic disease that afflicts 37 sub-Saharan African countries. There is a large arsenal of control tactics available to manage tsetse flies and the disease they transmit. The sterile insect technique (SIT) is a robust control tactic that has shown to be effective in eradicating tsetse populations when integrated with other control tactics in an area-wide integrated approach. The SIT requires production of sterile male flies in large production facilities. To supply sufficient numbers of sterile males for the SIT component against G. pallidipes, strategies have to be developed that enable the management of the Glossina hytrosavirus in the colonies. This review provides a historic chronology of the emergence and biogeography of Glossina hytrosavirus, and includes researches on the infectomics (defined here as the functional and structural genomics and proteomics) and pathobiology of the virus. Standard operation procedures for viral management in tsetse mass-rearing facilities are proposed and a future outlook is sketched. Full article
(This article belongs to the Special Issue Insect Pathology)
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Open AccessReview Immune Signaling and Antimicrobial Peptide Expression in Lepidoptera
Insects 2013, 4(3), 320-338; doi:10.3390/insects4030320
Received: 1 June 2013 / Revised: 21 June 2013 / Accepted: 21 June 2013 / Published: 2 July 2013
Cited by 6 | PDF Full-text (238 KB) | HTML Full-text | XML Full-text
Abstract
Many lepidopteran insects are agricultural pests that affect stored grains, food and fiber crops. These insects have negative ecological and economic impacts since they lower crop yield, and pesticides are expensive and can have off-target effects on beneficial arthropods. A better understanding of
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Many lepidopteran insects are agricultural pests that affect stored grains, food and fiber crops. These insects have negative ecological and economic impacts since they lower crop yield, and pesticides are expensive and can have off-target effects on beneficial arthropods. A better understanding of lepidopteran immunity will aid in identifying new targets for the development of specific insect pest management compounds. A fundamental aspect of immunity, and therefore a logical target for control, is the induction of antimicrobial peptide (AMP) expression. These peptides insert into and disrupt microbial membranes, thereby promoting pathogen clearance and insect survival. Pathways leading to AMP expression have been extensively studied in the dipteran Drosophila melanogaster. However, Diptera are an important group of pollinators and pest management strategies that target their immune systems is not recommended. Recent advances have facilitated investigation of lepidopteran immunity, revealing both conserved and derived characteristics. Although the general pathways leading to AMP expression are conserved, specific components of these pathways, such as recognition proteins have diverged. In this review we highlight how such comparative immunology could aid in developing pest management strategies that are specific to agricultural insect pests. Full article
(This article belongs to the Special Issue Insect Pathology)

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