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Melanins (eumelanin and pheomelanin) are synthesized in insects for several purposes including cuticle sclerotization and color patterning, clot formation, organogenesis, and innate immunity. Traditional views of insect immunity detail the storage of pro-phenoloxidases inside specialized blood cells (hemocytes) and their release upon recognition of foreign bodies. Activated phenoloxidases convert monophenols into reactive quinones in a two-step enzymatic reaction, and until recently, the mechanism of tyrosine hydroxylation remained a mystery. Herein, we present our interpretations of these enzyme-substrate complexes. The resultant melanins are deposited onto the surface of microbes to immobilize, agglutinate, and suffocate them. Phenoloxidase activity and melanin production are not limited to the blood (hemolymph) or cuticle, as recent evidence points to more diverse, sophisticated interactions in the gut and with the resident symbionts. This review offers insight into the somewhat neglected areas of insect melanogenesis research, particularly in innate immunity, its role in beneficial insects such as pollinators, the functional versatility of phenoloxidases, and the limitations of common experimental approaches that may impede progress inadvertently. [ABSTRACT FROM AUTHOR]

RNA interference (RNAi) methods for insects are often limited by problems with double-stranded (ds) RNA delivery, which restricts reverse genetics studies and the development of RNAi-based biocides. We therefore delegated to insect symbiotic bacteria the task of: (i) constitutive dsRNA synthesis and (ii) trauma-free delivery. RNaseIII-deficient, dsRNA-expressing bacterial strains were created from the symbionts of two very diverse pest species: a long-lived blood-sucking bug, Rhodnius prolixus, and a short-lived globally invasive polyphagous agricultural pest, western flower thrips (Frankliniella occidentalis). When ingested, the manipulated bacteria colonized the insects, successfully competed with the wild-type microflora, and sustainably mediated systemic knockdown phenotypes that were horizontally transmissible. This represents a significant advance in the ability to deliver RNAi, potentially to a large range of non-model insects. [ABSTRACT FROM AUTHOR]

Microevolutionary adaptations and mechanisms of fungal pathogen resistance were explored in a melanic population of the Greater wax moth, Galleria mellonella. Under constant selective pressure from the insect pathogenic fungus Beauveria bassiana, 25th generation larvae exhibited significantly enhanced resistance, which was specific to this pathogen and not to another insect pathogenic fungus, Metarhizium anisopliae. Defense and stress management strategies of selected (resistant) and non-selected (susceptible) insect lines were compared to uncover mechanisms underpinning resistance, and the possible cost of those survival strategies. We hypothesize that the insects developed a transgenerationally primed resistance to the fungus B. bassiana, a costly trait that was achieved not by compromising life-history traits but rather by prioritizing and re-allocating pathogen-species-specific augmentations to integumental front-line defenses that are most likely to be encountered by invading fungi. Specifically during B. bassiana infection, systemic immune defenses are suppressed in favour of a more limited but targeted repertoire of enhanced responses in the cuticle and epidermis of the integument (e.g. expression of the fungal enzyme inhibitor IMPI, and cuticular phenoloxidase activity). A range of putative stress-management factors (e.g. antioxidants) is also activated during the specific response of selected insects to B. bassiana but not M. anisopliae. This too occurs primarily in the integument, and probably contributes to antifungal defense and/or helps ameliorate the damage inflicted by the fungus or the host’s own immune responses. [ABSTRACT FROM AUTHOR]

When taking a blood meal on a person infected with malaria, female Anopheles gambiae mosquitoes, the major vector of human malaria, acquire nutrients that will activate egg development (oogenesis) in their ovaries. Simultaneously, they infect themselves with the malaria parasite. On traversing the mosquito midgut epithelium, invading Plasmodium ookinetes are met with a potent innate immune response predominantly controlled by mosquito blood cells. Whether the concomitant processes of mosquito reproduction and immunity affect each other remains controversial. Here, we show that proteins that deliver nutrients to maturing mosquito oocytes interfere with the antiparasitic response. Lipophorin (Lp) and vitellogenin (Vg), two nutrient transport proteins, reduce the parasite-killing efficiency of the antiparasitic factor TEP1. In the absence of either nutrient transport protein, TEP1 binding to the ookinete surface becomes more efficient. We also show that Lp is required for the normal expression of Vg, and for later Plasmodium development at the oocyst stage. Furthermore, our results uncover an inhibitory role of the Cactus/REL1/REL2 signaling cassette in the expression of Vg, but not of Lp. We reveal molecular links that connect reproduction and immunity at several levels and provide a molecular basis for a longsuspected trade-off between these two processes. [ABSTRACT FROM AUTHOR]

Anopheles gambiae mosquitoes are the principal vectors of malaria. A major determinant of the capacity of these mosquitoes as disease vectors is their high reproductive rate. Reproduction depends on a single insemination, which profoundly changes the behavior and physiology of females. To identify factors and mechanisms relevant to the fertility of A. gambiae, we performed a comprehensive analysis of the molecular and cellular machinery associated with copulation in females. Initial whole-body microarray experiments comparing virgins with females at 2 h, 6 h, and 24 h after mating detected large transcriptional changes. Analysis of tissue localization identified a subset of genes whose expression was strikingly regulated by mating in the lower reproductive tract and, surprisingly, the gut. In the atrium of virgin females, where the male seminal fluid is received, our studies revealed a "mating machinery" consisting of molecular and structural components that are turned off or collapse after copulation, suggesting that this tissue loses its competence for further insemination. In the sperm storage organ, we detected a number of mating-responsive genes likely to have a role in the maintenance and function of stored sperm. These results identify genes and mechanisms regulating the reproductive biology of A. gambiae females, highlighting considerable differences with Drosophila melanogaster. Our data inform vector control strategies and reveal promising targets for the manipulation of fertility in field populations of these important disease vectors. [ABSTRACT FROM AUTHOR]

The midgut epithelium of the mosquito malaria vector Anopheles is a hostile environment for Plasmodium, with most parasites succumbing to host defenses. This study addresses morphological and ultrastructural features associated with Plasmodium berghei ookinete invasion in Anopheles gambiae midguts to define the sites and possible mechanisms of parasite killing. We show by transmission electron microscopy and immunofluorescence that the majority of ookinetes are killed in the extracellular space. Dead or dying ookinetes are surrounded by a polymerized actin zone formed within the basal cytoplasm of adjacent host epithelial cells. In refractory strain mosquitoes, we found that formation of this zone is strongly linked to prophenoloxidase activation leading to melanization. Furthermore, we identify two factors controlling both phenomena: the transmembrane receptor frizzled-2 and the guanosine triphosphate-binding protein cell division cycle 42. However, the disruption of actin polymerization and melanization by double-stranded RNA inhibition did not affect ookinete survival. Our results separate the mechanisms of parasite killing from subsequent reactions manifested by actin polymerization and prophenoloxidase activation in the A. gambiae-P. berghei model. These latter processes are reminiscent of wound healing in other organisms, and we propose that they represent a form of wound-healing response directed towards a moribund ookinete, which is perceived as damaged tissue. [ABSTRACT FROM AUTHOR]

This study examines how the dynamics of fungus-insect interactions can be modulated by temperature. The wax moth, Galleria mellonella, is a well-studied and important model insect whose larvae in the wild develop optimally at around 34 °C in beehives.However, surprisingly little research onwaxmoths has been conducted at relevant temperatures. In this study, the entomopathogenic fungus Metarhizium robertsii inflicted rapid and substantial mortality on wax moth larvae maintained at a constant temperature of 24 °C, but at 34 °C a 10 fold higher dose was required to achieve an equivalent mortality. The cooler temperature favored fungal pathogenicity, with condial adhesion to the cuticle, germination and hemocoel invasion all significantly enhanced at 24 °C, compared with 34 °C. Thewax moth larvae immune responses alteredwith the temperature, and with the infective dose of the fungus. Enzyme-based immune defenses (lysozyme and phenoloxidase) exhibited enhanced activity at the warmer temperature. A dramatic upregulation in the basal expression of galiomicin and gallerimycin was triggered by cooling, and thiswas augmented in the presence of the fungus. Profiling of the predominant insect epicuticular fatty acids revealed a 4-7 fold increase in palmetic, oleic and linoleic acids in larvae maintained at 24 °C compared with those at 34 °C, but these failed to exert fungistatic effects on topically applied fungus. This study demonstrates the importance of choosing environmental conditions relevant to the habitat of the insect host when determining the dynamics and outcome of insect/fungus interactions, and has particular significance for the application of entomopathogens as biocontrol agents. [ABSTRACT FROM AUTHOR]

Microevolutionary mechanisms of resistance to a bacterial pathogen were explored in a population of the Greater wax moth,Galleria mellonella, selected for an 8.8-fold increased resistance against the entomopathogenic bacteriumBacillus thuringiensis(Bt) compared with a non-selected (suspectible) line. Defense strategies of the resistant and susceptible insect lines were compared to uncover mechanisms underpinning resistance, and the possible cost of those survival strategies. In the uninfected state, resistant insects exhibited enhanced basal expression of genes related to regeneration and amelioration of Bt toxin activity in the midgut. In addition, these insects also exhibited elevated activity of genes linked to inflammation/stress management and immune defense in the fat body. Following oral infection with Bt, the expression of these genes was further elevated in the fat body and midgut of both lines and to a greater extent some of them in resistant line than the susceptible line. This gene expression analysis reveals a pattern of resistance mechanisms targeted to sites damaged by Bt with the insect placing greater emphasis on tissue repair as revealed by elevated expression of these genes in both the fat body and midgut epithelium. Unlike the susceptible insects, Bt infection significantly reduced the diversity and richness (abundance) of the gut microbiota in the resistant insects. These observations suggest that the resistant line not only has a more intact midgut but is secreting antimicrobial factors into the gut lumen which not only mitigate Bt activity but also affects the viability of other gut bacteria. Remarkably the resistant line employs multifactorial adaptations for resistance to Bt without any detected negative trade off since the insects exhibited higher fecundity. [ABSTRACT FROM PUBLISHER]

Abstract: Members of the subfamily Triatominae, family Reduviidae, comprise a large number of insect species of which some are vectors of Trypanosoma cruzi, the causative agent of Chagas’ disease. This article outlines research on the process of transformation and the dynamics of developmental stages of Trypanosoma cruzi in the triatomine insect hosts. Special attention is given to the interactions of parasites with gut molecules, and the gut environment, and with host developmental physiology and intestinal organization. The vector insect''s permissiveness to Trypanosoma cruzi, which develops in the vector gut, largely depends on the host nutritional state, the parasite strain, trypanolytic compounds, digestive enzymes, lectins, resident bacteria in the gut and the endocrine system of the insect vector. Finally, the mechanisms of these interactions and their significance for Trypanosoma cruzi transmission are discussed. [Copyright &y& Elsevier]

Obligate bacterial symbionts are widespread in many invertebrates, where they are often confined to specialized host cells and are transmitted directly from mother to progeny. Increasing numbers of these bacteria are being characterized but questions remain about their population structure and evolution. Here we take a comparative genomics approach to investigate two prominent bacterial symbionts (BFo1 and BFo2) isolated from geographically separated populations of western flower thrips, Frankliniella occidentalis. Our multifaceted approach to classifying these symbionts includes concatenated multilocus sequence analysis (MLSA) phylogenies, ribosomal multilocus sequence typing (rMLST), construction of whole-genome phylogenies, and in-depth genomic comparisons. We showed that the BFo1 genome clusters more closely to species in the genus Erwinia, and is a putative close relative to Erwinia aphidicola. BFo1 is also likely to have shared a common ancestor with Erwiniapyrifoliae/Erwinia amylovora and the nonpathogenic Erwinia tasmaniensis and genetic traits similar to Erwinia billingiae. The BFo1 genome contained virulence factors found in the genus Erwinia but represented a divergent lineage. In contrast, we showed that BFo2 belongs within the Enterobacteriales but does not group closely with any currently known bacterial species. Concatenated MLSA phylogenies indicate that it may have shared a common ancestor to the Erwinia and Pantoea genera, and based on the clustering of rMLST genes, it was most closely relatedtoPantoea ananatis but represented adivergent lineage. We reconstructed a core genome of a putative common ancestor of Erwinia and Pantoea and compared this with the genomes of BFo bacteria. BFo2 possessed none of the virulence determinants that were omni present in the Erwinia and Pantoea genera. Taken together, these data are consistent with BFo2 representing a highly novel species that maybe related to known Pantoea. [ABSTRACT FROM AUTHOR]

Background: There are varying degrees of compatibility between malaria parasite-mosquito species, and understanding this compatibility may be crucial for developing effective transmission-blocking vaccines. This study investigates the compatibility of different biological forms of a malaria vector, Anopheles stephensi, to Plasmodium berghei ANKA strain. Methods: Several biologically different and allopatric forms of A. stephensi were studied. Three forms were isolated from different regions of southern Iran: the variety mysorensis, the intermediate form and the native type form, and an additional type form originated from India (Beech strain).The mosquitoes were experimentally infected with P. berghei to compare their susceptibility to parasitism. Anti-mosquito midgut antiserum was then raised in BALB/cs mice immunized against gut antigens from the most susceptible form of A. stephensi (Beech strain), and the efficacy of the antiserum was assessed in transmission-blocking assays conducted on the least susceptible mosquito biological form. Results: The susceptibility of different biological forms of A. stephensi mosquito to P. berghei was specifically inter-type varied. The Beech strain and the intermediate form were both highly susceptible to infection, with higher oocyst and sporozoite infection rates than intermediate and mysorensis forms. The oocyst infection, and particularly sporozite infection, was lowest in the mysorensis strain. Antiserum raised against midgut proteins of the Indian Beech type form blocked infection in this mosquito population, but it was ineffective at blocking both oocyst and sporozoite development in the permissive but geographically distant intermediate form mosquitoes. This suggests that a strong degree of incompatibility exists between the mosquito strains in terms of midgut protein(s) acting as putative ookinete receptors. Conclusions: The incompatibility in the midgut protein profiles between two biological forms of A. stephensi demonstrates a well-differentiated population structure according to geographical origin. Therefore, the design of potential transmission-blocking strategies should incorporate a more thorough understanding of intra-species variations in host-parasite interactions. [ABSTRACT FROM AUTHOR]

Background: Despite the abundance of studies conducted on the role of mosquitoes in malaria transmission, the biology and interaction of Plasmodium with its insect host still holds many mysteries. This paper provides the first study to follow the sporogonic cycle of Plasmodium vivax in a wild insecticide-resistant mysorensis strain of Anopheles stephensi, a major vector of vivax malaria in south-eastern Iran. The study subsequently demonstrates that host-parasite sugar binding interactions are critical to the development of this parasite in the salivary glands of its mosquito host. The identity of the receptors or sugars involved was revealed by a receptor "pre-saturation" strategy in which sugars fed to the mosquitoes inhibited normal host-parasite interactions. Methods: Anopheles stephensi mysorensis mosquitoes were artificially infected with P. vivax by feeding on the blood of gametocytaemic volunteers reporting to local malaria clinics in the Sistan-Baluchistan province of southeastern Iran. In order to determine the inhibitory effect of carbohydrates on sporogonic development, vector mosquitoes were allowed to ingest blood meals containing both gametocytes and added carbohydrates. The carbohydrates tested were GlcNAc, GalNAc, arabinose, fucose, mannose, lactose, glucose and galactose. Sporogonic development was assessed by survival of the parasite at both the oocyst and sporozoite stages. Results: Oocyst development was observed among nearly 6% of the fed control mosquitoes but the overall number of mosquitoes exhibiting sporozoite invasion of the salivary glands was 47.5% lower than the number supporting oocysts in their midgut. Of the tested carbohydrates, only arabinose and fucose slightly perturbed the development of P. vivax oocysts at the basal side of the mosquito midgut, and the remaining sugars caused no reductions in oocyst development. Strikingly however, sporozoites were completely absent from the salivary glands of mosquitoes treated with mannose, GalNAc, and lactose. Conclusion: The study indicates that An. stephensi in southern Iran has the potential to survive long enough to be re-infected and transmit vivax malaria several times, based on the average adult female longevity (about 30 days) and its gonotrophic cycle (2-3 days) during the malaria transmission season. Certain sugar binding interactions are important for the development of P. vivax sporozoites, and this information may be instrumental for the development of transmission blocking strategies. [ABSTRACT FROM AUTHOR]