Special Issue "Insect Immunity"

Guest Editor
Dr. Brian P. Lazzaro
Department of Entomology, 3134 Comstock Hall, Cornell University, Ithaca, NY 14853, USA
Website: http://www.lazzaro.entomology.cornell.edu
E-Mail: bplazzaro@cornell.edu

Dear Colleagues,

The study of infection and immunity in insects has grown to considerable prominence over the past several decades. Early work in the 1950s, 1960s and 1970s focused on the biochemistry of insect immunity and the (fruitless) search for insect analogs of vertebrate antibodies. A transformational element of functional genetics emerged in the 1990s, emphasizing the Drosophila model system, with work from this era earning a share of the 2011 Nobel Prize in Physiology or Medicine. The emergence of widespread genome sequencing in the 2000s allowed comparative genomic analyses that revealed the strikingly high degree of conservation in immune system genes even across insects hundreds of millions of years diverged. The study of insect immunity is now extraordinarily multidisciplinary. Because fundamental aspects of the immune system are conserved across all animals, insects can serve as valuable biomedical models for the study of immune system function and pathogen virulence. The study of insect immunity is also important in its own right, with managed infection at the core of new approaches to the biological control of insect agricultural pests and vectors of human disease. The interactions between insects and their pathogens continue to elucidate basic principles in evolutionary biology, ecology, and the epidemiology of infectious disease. We wish to use this special issue of Insects to highlight the diversity and depth of research into the functional biology, evolution, and translational application of infection and immunity in insects.

Dr. Brian P. Lazzaro
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.

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David Stanley, Eric Haas and Jon Miller Review: Eicosanoids: Exploiting Insect Immunity to Improve Biological Control Programs Insects 2012, 3(2), 492-510; doi:10.3390/insects3020492 Received: 15 March 2012; in revised form: 24 April 2012 / Accepted: 9 May 2012 / Published: 16 May 2012 Show/Hide Abstract | Download PDF Full-text (379 KB) | View HTML Full-text | Download PMC-XML Full-text Abstract: Insects, like all invertebrates, express robust innate, but not adaptive, immune reactions to infection and invasion. Insect immunity is usually resolved into three major components. The integument serves as a physical barrier to infections. Within the hemocoel, the circulating hemocytes are the temporal first line of defense, responsible for clearing the majority of infecting bacterial cells from circulation. Specific cellular defenses include phagocytosis, microaggregation of hemocytes with adhering bacteria, nodulation and encapsulation. Infections also stimulate the humoral component of immunity, which involves the induced expression of genes encoding antimicrobial peptides and activation of prophenoloxidase. These peptides appear in the hemolymph of challenged insects 6–12 hours after the challenge. Prostaglandins and other eicosanoids are crucial mediators of innate immune responses. Eicosanoid biosynthesis is stimulated by infection in insects. Inhibition of eicosanoid biosynthesis lethally renders experimental insects unable to clear bacterial infection from hemolymph. Eicosanoids mediate specific cell actions, including phagocytosis, microaggregation, nodulation, hemocyte migration, hemocyte spreading and the release of prophenoloxidase from oenocytoids. Some invaders have evolved mechanisms to suppress insect immunity; a few of them suppress immunity by targeting the first step in the eicosanoid biosynthesis pathways, the enzyme phospholipase A2. We proposed research designed to cripple insect immunity as a technology to improve biological control of insects. We used dsRNA to silence insect genes encoding phospholipase A2, and thereby inhibited the nodulation reaction to infection. The purpose of this article is to place our view of applying dsRNA technologies into the context of eicosanoid actions in insect immunity. The long-term significance of research in this area lies in developing new pest management technologies to contribute to food security in a world with a rapidly growing human population.

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Type of Paper: Review
Title: Behavioral Immunity in Insects
Authors: Jacobus C. de Roode and Thierry Lefèvre
Affiliation: Department of Biology, Emory University, 1510 Clifton Road, Atlanta GA 30322, USA; E-Mail: jacobus.de.roode@gmail.com
Abstract: Parasites can dramatically reduce the fitness of their hosts, and natural selection should favor defense mechanisms that can protect hosts against disease. Much work has focused on understanding genetic and physiological immunity against parasites, but hosts can also use behaviors to avoid infection, reduce parasite growth or alleviate disease symptoms. It is increasingly recognized that such behaviors are common in insects, providing strong protection against parasites and parasitoids. We review the current evidence for behavioral immunity in insects, present a framework for investigating such behavior, and emphasize that behavioral immunity may act through indirect rather than direct fitness benefits. We also discuss the implications for host-parasite co-evolution, local adaptation, and the evolution of physiological immune systems. Finally, we argue that the study of behavioral immunity in insects has much to offer for investigations in vertebrates, in which this topic has traditionally been studied.

Type of Paper: Article
Title: How Varroa parasitism Affects the Nutritional and Immunological Status of the Honey Bee, Apis mellifera
Authors: K.A. Aronstein ¹, E. Saldivar ¹, E.R. Vega ², S. Westmiller ² and A.E. Douglas ²
Affiliation: ¹ Honey Bee Research Unit, USDA-ARS, Weslaco, TX 78596, USA; E-Mail: Kate.Aronstein@ARS.USDA.GOV
² Department of Entomology, Cornell University, Ithaca, NY 14853, USA
Abstract: Varroa destructor (Acari: Varroidae), a parasitic mite of the honey bee (Hymenoptera: Apidae), was first discovered in the US in 1987. Since then, Varroa infestation of managed bees has become one of the most urgent problems facing the beekeeping industry, but the mechanisms by which honey bee health is impaired are not understood fully. Previously unpublished empirical data on the effect of Varroa on the immunological and nutritional status of the honey bee at the level of the individual insect and the colony are used to investigate the physiological relationship between immune function and nutritional condition, and to address how the immunocompetence and nutritional status of individual bees shape the overall health of the colony.

Type of Paper: Article
Title: cDNA Cloning and Expression Analysis of Pattern Recognition Proteins from the Chinese Oak Silkmoth, Antheraea pernyi
Authors: Fengjuan Li¹, Olle Terenius^2,*, Yuan Li¹, Suyun Fang¹ and Wenli Li¹
Affiliations: ¹School of Bioscience and Biotechnology, Dalian University of Technology, Dalian, 116023 Liaoning, PR. China; E-Mail: biolwl@dlut.edu.cn
²Department of Ecology, Swedish University of Agricultural Sciences (SLU), 750 07 Uppsala, Sweden; E-Mail: Olle.Terenius@slu.se
Abstract: Pattern recognition receptors play an important role in insect immune defense. We cloned the β-1,3-glucan recognition protein, immunlectin-5 and immunolectin-A genes of Antheraea pernyi and examined the expression profiles of immune-stimulated pupae. After infection with Bacillus subtilis, Escherichia coli, Antheraea pernyi nuclear polyhedrosis virus (ApNPV) and Saccharomyces cerevisiae respectively, the pupae showed different expression levels in the different tissues examined (midgut, fatbody, epidermis, testis, and hemocytes). ApβGRP was induced by the Gram-positive bacterium, while immunolectin-5 and immunolectin-A were induced by both bacteria and the fungus, and immunolectin-A in addition by the virus infection. Whereas immunolectin-5 was expressed mainly in epidermis, immunolectin-A had its highest expression in fatbody indicating that both function and localization of the immunolectins complemented each other.

Type of Paper: Review
Title: Influences of plant traits on immune responses of specialist and generalist herbivores
Author: Evan Lampert
Affiliation: Department of Biological Sciences, Gainesville State College, Oakwood, GA 30566, USA; E-Mail: elampert@gsc.edu
Abstract: Specialist and generalist herbivore species often differ in how they respond to host plant traits, particularly defensive traits, and these responses can include weakened or strengthened immune responses to pathogens and parasites. Accurate methods to measure immune response in the presence and absence of pathogens and parasites are necessary to determine whether susceptibility to these natural enemies is reduced or increased by host plant traits. Plant chemical traits are particularly important in that host plants may provide precursors and intermediates of encapsulation and melanization pathways in both specialist and generalists. Specialist species that are adapted to process and sometimes accumulate specific plant compounds may experience high metabolic demands that decrease immune response, whereas the metabolic demands of generalist species differ due to more broad-substrate enzyme systems. However, the deleterious effects of plant compounds on generalist species may weaken their immune responses. An understanding of the ecological importance of plant traits to herbivore immune responses is equally important in natural systems and agroecosystems, due to potential incompatibility of host plant species and cultivars with biological control agents of herbivorous pests.

Type of Paper: Article
Title: Do Females Prefer Males with Similar Personality? An Analysis of Boldness, Mate Choice and Bacterial Resistance in the Field Cricket Gryllus Integer
Authors: R. Kortet¹, P. Niemelä^1,2, A. Vainikka^1,2, J. Laakso³
Affiliations: ¹Department of Biology, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland; E-Mail: raine.kortet@uef.fi
²Department of Biology, University of Oulu, P.O. Box 3000, FI-90014 University of Oulu, Finland          
³Department of Biosciences, P.O. Box 65, FI-00014 University of Helsinki, Finland
Abstract: Recent theory predicts that personality traits contributing to resource intake rates could reflect individual’s condition-dependent capacity to resist parasites and pathogens. Since females often prefer mates with strong immune defence, females could potentially gain fitness benefits by using male’s behavioural type as one mate choice criteria. We studied if females in the field cricket Gryllus integer would base their mate choice on male boldness and if the boldness would predict survival under experimental challenge to opportunist bacterial pathogen Serratia marcenscens. In addition, we tested if different females would prefer the same males. Boldness did not explain individual’s lifespan in experimental infection. All the three females preferred one male within pair over the other male in 26.9 % of the mate choice tests, but the preferred male varied between the females, and females showed tendency to prefer shy males. Our results suggest that females may show preferences for certain behavioural types, but that male boldness may not reflect his capacity to resist bacterial pathogens.

Type of Paper: Article
Title: The Effect of West Nile Virus Infection on the Midgut Gene Expression of Culex Pipiens Quinquefasciatus Say (Diptera: Culicidae)
Authors: C. T. Smartt and S. L. Anderson
Affiliation: Florida Medical Entomology Laboratory, Department of Entomology and Nematology, University of Florida – IFAS, Vero Beach, Florida 32962; E-Mail: ctsmart@ufl.edu
Abstract: The interaction of the mosquito and the invading parasite is complex and can result in physiological and gene expression alterations in the insect. We have previously shown that the association of West Nile virus (WNV) and one of its mosquito vectors Culex pipiens quinquefasciatus results in measureable changes in gene expression; 22 gene products were shown to have altered expression. Sequence analysis of one gene product, CQ G1A1, was performed and revealed the putative translation product was 81% identical to a gram negative bacteria binding protein (GNBP) in Cx. p. quinquefasciatus, Aedes aegypti (70%) and Anopheles gambiae (63%). Gram negative bacteria binding proteins are involved in pathogen recognition that results in the activation of the innate immune response in insects. Gene expression analysis in midgut tissues of mosquitoes fed WNV revealed that the expression increased 1 day post infection (dpi) through 3 dpi and these time points coincided with a decrease in WNV titer. Besides differential expression in midgut tissue following WNV infection, CQ G1A1 was differentially expressed between two populations of Cx. p. quinquefasciatus colonized from two regions of Florida with known differences in vector competence for WNV. These data suggest a role for CQ G1A1 in mosquito innate immune response to infection with WNV.  Sequence analysis of PCR generated fragments corresponding to a second message, CQ G43A, was performed and revealed the putative translation product was 98% identical to a defensin-like protein (DEF-A) in Cx. p. quinquefasciatus and Aedes aegypti (75%). Defensin proteins are involved in antibacterial response in many vertebrates and invertebrates. Expression analysis of CQ G43A in midguts from WNV infected mosquitoes did not differ from expression in midguts from uninfected mosquitoes, although expression levels were considerably higher than CQ G1A1 in the same midgut samples. The involvement of these midgut genes in the immune response against WNV infection of Cx. p. quinquesfasciatus implicates multiple antiviral pathways in the ability of a mosquito to manage infection with WNV.

Type of Paper: Article
Title: Incidence of Behavioural, Physiological and Chemical Defenses of Soil White Grubs on Parasitism Success of Mallophora Ruficauda Larva (Diptera: Asilidae)
Authors: M.K. Castelo and J.E. Crespo
Affiliation: Grupo de Investigación en Ecofisiología de Parasitoides (GIEP). CONICET-IEGEBA-Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria, Pabellon II, 4° piso, lab. 99 (C1428EHA), Buenos Aires, Argentina; E-Mail: mcastelo@ege.fcen.uba.ar
Abstract: White grubs are larvae of Coleoptera of the family Scarabaeidae that are attacked by the larvae of the ectoparasitoid Mallophora ruficauda (Diptera: Asilidae). The objectives of this work were to investigate what kind of defense and associated mechanisms do the white grubs have against this parasitoid and why does M. ruficauda have a high preference for C. signaticollis. For several white grubs species we evaluated the reaction when a parasitoid attack is simulated, the fraction of hosts that escapes from parasitism, and if hosts release attractive odours for parasitoids. We found that mainly behavioural and chemical defenses of white grubs are involved in avoiding parasitism of M. ruficauda.

Type of Paper: Review
Title: Endosymbiont Tolerance and Control Within Insect Hosts
Authors: C. Ratzka ¹, R. Gross ¹ and H. Feldhaar ²
Affiliations: ¹ Lehrstuhl für Mikrobiologie, Biozentrum, Universität Würzburg, Germany
² Animal Ecology I, University of Bayreuth, Germany; E-Mail: feldhaar@uni-bayreuth.de
Abstract: Bacterial endosymbioses are very common in insects and can range from obligate to facultative as well as from mutualistic to pathogenic associations. Several recent studies provide new insights how endosymbionts manage to establish chronic infections of their hosts without being eliminated by the host immune system. Endosymbiont tolerance may be achieved either through specific bacterial adaptations or by host measurements shielding bacteria from innate defense mechanisms. Nevertheless, insect hosts also need to sustain control mechanisms to prevent endosymbionts from unregulated proliferation. Emerging evidence indicates that in some cases the mutual adaptations of the two organisms may have led to the integration of the endosymbionts as a part of the host immune system. In fact endosymbionts may provide protective traits against pathogens and predators and may even be required for the proper development of the host immune system during host ontogeny. This review gives an overview of current knowledge of molecular mechanisms ensuring maintenance of chronic infections with mutualistic endosymbionts and the impact of endosymbionts on host immune competence.

Type of the Paper: Review
Title: New Insights into Control of Arbovirus Replication and Spread by Insect RNA Interference Pathways
Authors: Claire L. Donald, Alain Kohl  and Esther Schnettler
Affiliations: MRC-University of Glasgow Centre for Virus Research, 8 Church Street, Glasgow G11 5JR, Scotland, UK; E-Mails: c.donald.1@research.gla.ac.uk (C.L.D.); alain.kohl@glasgow.ac.uk (A.K.); esther.schnettler@glasgow.ac.uk (E.S.)
Abstract: Arboviruses are transmitted by vectors, such as mosquitoes, to susceptible vertebrates. Recent research has shown that arbovirus replication and spread in mosquitoes is not passively tolerated but induces host responses to control these pathogens. Small RNA-mediated host responses are key players among these antiviral immune strategies. Studies into one such small RNA-mediated antiviral response, the exogenous RNA interference (RNAi) pathway, has generated a wealth of information on the functions of this mechanism and the enzymes which mediate antiviral activities. However, other small RNA-mediated host responses may also be involved in modulating antiviral activity. The aim of this review is to summarize recent research into the nature of small RNA-mediated antiviral responses in mosquitoes and to discuss future directions for this relatively new area of research.