Non-sibling parasites (Strepsiptera) develop together in the same paper wasp

Host discrimination by immature host-seeking endoparasites is a complex and somewhat unexplored topic. In the case of multiple infections, conflicts among conspecifics may occur to monopolize space and resources in the same host. Two or more 1st instar larvae of Xenos vesparum (Strepsiptera, Stylopidae) may enter into a Polistes dominulus (Hymenoptera, Vespidae) larva and develop together until the adult stage of both parasite and host. We carried out a screening of mitochondrial haplotypes in X. vesparum individuals extracted from superparasitized wasps taken in 5 naturally infected nests from different areas of Tuscany (Italy), to assess whether non-sibling parasites may infect the same colony and host. In total, we obtained 12 different haplotypes out of 122 genotyped individuals of both sexes: 17 of 34 superparasitized wasps hosted parasites that originated from females differing in their haplotypes. To date, this is the first described case of superparasitism with non-sibling host-seeking larvae infecting a single individual hymenopteran host. In addition, at least in heavily infected colonies, there is evidence of a male-biased sex-ratio and synchronous development of the parasites, regardless of their haplotypes. Finally, the distribution of haplotypes per nest is consistent with either phoretic infection or larvipositing on nests by means of superparasitized wasps.     

Hyperparasitism by Paragordius varius (Nematomorpha: Gordiida) larva of Monostome redia (Trematoda: Digenea)

Gordiid larvae enter and encyst within a large variety of aquatic vertebrates and invertebrates. Cysts of a single species of gordiid have been found in such diverse hosts as insect larvae, snails, crustaceans, fish, and many others. One particularly surprising host report was made nearly 100 yr ago, i.e., cysts within adult trematodes. The origin of these cysts remained unclear, but it was suggested that the gordiid larvae gained entry into the adult flukes via their definitive, vertebrate host. In the present study, the finding is reported of gordiid cysts within monostome redia within a Physa gyrina snail. This is the first time gordiid cysts have been reported within redia, and this provides an alternative explanation for the presence of cysts within adult trematodes.     

Behavioural response to an unsuitable host plant in the gypsy moth (Lymantria dispar L.)

To assess local differentiation in host preference, a two-choice test was performed on first-instar gypsy moth larvae originating from an oak and locust-tree forest. More than 40 generations feeding on locust-tree leaves, rich in alkaloids, led to non-efficient discrimination of host leaves in larvae from a locust-tree forest. Possible causes of observed population differences are discussed in the present paper.     

The life history and larval morphology of Aperilampus (Hymenoptera: Chalcidoidea: Philomidinae), with a discussion of the phylogenetic affinities of the Philomidinae

Abstract. The host association and larval morphology of Aperilampus (Hymenoptera: Chalcidoidea: Philomidinae) are documented for the first time based on specimens collected during the excavation of ground-nesting bee nests in South Africa. Aperilampus varians Strand is a primary parasite of the pupa of Halictus (Seladonia) africanus Friese (Hymenoptera: Halictidae). The first and final-instar larvae are described and illustrated, and notes are provided on the behaviour of the first-instar larva. The first-instar larva is a planidium and synapomorphies are documented between the first-instar larva of Aperilampus and the planidia of Chrysolampinae, Perilampidae and Eucharitidae.     

The evolution of Strepsiptera (Hexapoda)

An evolutionary scenario for the enigmatic group Strepsiptera is provided, based on the results of a comprehensive cladistic analysis of characters of all life stages. A recently described fossil--+Protoxenos janzeni--the most archaic strepsipteran, sheds new light on the early evolution of the group and reduces the "morphological gap" between Strepsiptera and other insects. It weakens both current hypotheses--Coleoptera+Strepsiptera and Diptera+Strepsiptera (="Halteria"). The splitting into +Protoxenos (Protoxenidae) and the remaining Strepsiptera was linked with a distinct size reduction and many morphological changes. Unlike males of extant strepsipteran species, +Protoxenos was still able to process food. Mengeidae (+Mengea), with two small species, is the sister group of extant Strepsiptera. A unique characteristic of extant males (Strepsiptera s. str.) is the mouthfield sclerite. It is part of an air uptake apparatus which belongs to an extremely modified air-filled "balloon gut". Besides this, male strepsipterans possess specialised antennae and compound eyes, a strongly developed flight apparatus, large testes, and a sperm pump, whereas other organ systems are strongly reduced (e.g., fat body, malpighian tubules). Males are designed to find females within a few hours and to copulate. A dramatic change is linked with the split into Mengenillidae and Stylopidia. The change to pterygote hosts and the permanent endoparasitism of the females are evolutionary novelties acquired by the latter clade, and linked with far-reaching morphological transformations, e.g. the presence of unique brood organs. Hairy tarsal adhesive devices are present in males and guarantee efficient attachment to the host during copulation. A well-founded clade within Stylopidia is Stylopiformia, which are characterised by a unique fissure-shaped birth opening. The evolutionary development towards the most specialised and successful forms (parasites of aculeate Hymenoptera [e.g., Xenidae+Stylopidae], ca. 46% of the species) is a stepwise process. The presented evolutionary scenario comprises a complex network of functionally correlated morphological changes in primary larvae, secondary larvae, females and males.     

Lipid rafts,caveolae, caveolin-1, and entry by Chlamydiae into host cells

Obligate intracellular bacterial pathogens of the genus Chlamydia are reported to enter host cells by both clathrin-dependent and clathrin-independent processes. C. trachomatis serovar K recently was shown to enter cells via caveolae-like lipid raft domains. We asked here how widespread raft-mediated entry might be among the Chlamydia. We show that C. pneumoniae, an important cause of respiratory infections in humans that additionally is associated with cardiovascular disease, and C. psittaci, an important pathogen in domestic mammals and birds that also infects humans, each enter host cells via cholesterol-rich lipid raft microdomains. Further, we show that C. trachomatis serovars E and F also use these domains to enter host cells. The involvement of these membrane domains in the entry of these organisms was indicated by the sensitivity of their entry to the raft-disrupting agents Nystatin and filipin, and by their intracellular association with caveolin-1, a 22-kDa protein associated with the formation of caveolae in rafts. In contrast, caveolin-marked lipid raft domains do not mediate entry of C. trachomatis serovars A, 36B, and C, nor of LGV serovar L2 and MoPn. Finally, we show that entry of each of these chlamydial strains is independent of cellular expression of caveolin-1. Thus, entry via the Nystatin and filipin-sensitive pathway is dependent on lipid rafts containing cholesterol, rather than invaginated caveolae per se.     

Histological and immunological reaction of cattle skin to first-instar larvae of Dermatobia hominis

Abstract. Six cattle that had earlier exposure to Dermatobia hominis were infested experimentally with first-instar larvae of the parasite. Skin biopsies taken at intervals were studied in wax and in plastic sections. The avidin-biotin-peroxidase method was used to detect the presence and localization of host immunoglobulins (Igs) G and M and antigens of first and second instar larvae of Dermatobia hominis. The larvae penetrated actively through the skin and migrated towards the subcutaneous tissues. The great numbers of eosinophils suggest that they are the most important cell in mediating damage to D.hominis larvae. The immunoglobulins bound only to dead or moulting larvae in which access to binding sites may have been altered. This could represent a morphological manifestation of a mechanism that protects larvae from the host immune response. Large amounts of soluble antigens detected along the fistulous tract may be important in the maintenance of this tract by disturbing the normal cicatrization process.     

The parasitoidCotesia glomerata (Hymenoptera: Braconidae) discriminates between first and fifth larval instars of its hostPieris brassicae,on the basis of contact cues from frass,silk, and herbivore-damaged leaf tissue

Adult females of the larval parasitoidCotesia glomerata (L.) respond to chemical cues associated with feeding damage inflicted on cabbage plants by its host,Pieris brassicae (L.). The use of these infochemicals by the parasitoid during selection of the most suitable host instar was investigated. The parasitoid can successfully parasitize first-instar host larvae, while contacts with fifth-instar larvae are very risky since these caterpillars react to parasitization attempts by biting, spitting, and hitting, resulting in a high probability of the parasitoid being seriously injured or killed. Observations of the locomotor behavior of individual wasps on leaves with feeding damage inflicted by the first and the fifth larval instars and on host silk and frass showed that several cues affect the duration of searching by the parasitoids after reaching a leaf: cues on the margin of the feeding damage and cues in the host frass and silk. Whole frass, silk, and hexane extracts of frass obtained from first-instar elicited parasitoid's searching behavior significantly longer than frass, silk, and hexane extract of frass from the fifth instar. The results demonstrate thatC. glomerata can discriminate between first instars, which are more suitable hosts, and fifth instars ofP. brassicae without contacting the caterpillars, by exploiting instar-related cues.     

Phylogeny of the Strepsiptera based on morphological data of the first instar larvae

This investigation was the first cladistic analysis using morphological data of first instar larvae of Strepsiptera. The analysis of representatives of nearly all known families of Strepsiptera supports the division of Strepsiptera into Mengenillidia and Stylopidia. Corioxenidae and Elenchidae are placed at the base of Stylopidia. Halictophagidae is the sister group to Xeninae + Myrmecolacidae + Stylopinae. Xeninae is placed as the sister group to Myrmecolacidae + Stylopinae. Stylopidae are paraphyletic. Thus, Xenidae stat. n. is re-established. A sister-group relationship between Myrmecolacidae and Elenchidae is not supported on characters of first instar larvae.     

Developmental strategy of the endoparasite Xenos vesparum (strepsiptera, Insecta): host invasion and elusion of its defense reactions

To successfully complete its endoparasitic development, the strepsipteran Xenos vesparum needs to elude the defense mechanisms of its host, the wasp Polistes dominulus. SEM and TEM observations after artificial infections allow us to outline the steps of this intimate host-parasite association. Triungulins, the mobile 1st instar larvae of this parasite, are able to "softly" overcome structural barriers of the larval wasp (cuticle and epidermis) without any traumatic reaction at the entry site, to reach the hemocoel where they settle. The parasite molts 48 h later to a 2nd instar larva, which moves away from the 1st instar exuvium, molts twice more without ecdysis (a feature unique to Strepsiptera) and pupates, if male, or develops into a neotenic female. Host encapsulation involves the abandoned 1st larval exuvium, but not the living parasite. In contrast to the usual process of encapsulation, it occurs only 48 h after host invasion or later, and without any melanization. In further experiments, first, we verified Xenos vesparum's ability to reinfect an already parasitized wasp larva. Second, 2nd instar larvae implanted in a new host did not evoke any response by hemocytes. Third, we tested the efficiency of host defense mechanisms by implanting nylon filaments in control larval wasps, excluding any effect due the dynamic behavior of a living parasite; within a few minutes, we observed the beginning of a typical melanotic encapsulation plus an initial melanization in the wound site. We conclude that the immune response of the wasp is manipulated by the parasite, which is able to delay and redirect encapsulation towards a pseudo-target, the exuvia of triungulins, and to elude hemocyte attack through an active suppression of the immune defense and/or a passive avoidance of encapsulation by peculiar surface chemical properties.     

Invasion of black-tailed deer by nose bot fly larvae (Diptera: Oestridae: Oestrinae)

Invasion of black-tailed deer (Odocoileus hemionus columbianus) by larvae of the nose bot flies (Cephenemyia apicata and C. jellisoni) was investigated by obssrving their expulsion by larviparous females and their subsequent activity on the host. The drying uterine fluid encasing larvae ( = larval packet) delays desiccation, ensures adhesion to hairs, and immediately dissolves upon contact with saliva. Contrary to the widely accepted nasal mode of invasion, larvae placed on muzzles of deer crawl ventrally toward the upper lip, enter the mouth, and then crawl caudally along the hard palate or tongue toward the throat. Hair located between the muzzle and nostril prevents larvae from entering the nostrils. A natural per os mode of invasion, heretofore unrecognized, is proposed. This is initiated by: (1) females depositing larval packets on the muzzle of deer, or (2) deer licking larval packets from contaminated areas around the muzzle. The positive thermotropism of larvae is compatible with such a per os mode of entry into the host.     

The mode of transmission of Tipula iridescent virus: II. Route of infection

Tipula iridescent virus (TIV) was inoculated into Tipula oleracea larvae via different routes. It was found to be much more infective when it was injected into the hemocoel than when it was ingested by the larvae.T. oleracea embryos did not become infected when eggs were laid in agar containing TIV, and there was no evidence that larvae can become infected via the spiracles or that transovum transmission occurs. It is suggested that TIV is transmitted principally by cannibalism, including killing and ingesting infected larvae, and finding dead infected larvae and ingesting them. It is proposed that a new generation becomes infected by first-instar larvae feeding upon infected fourth-instar larvae which have survived from the previous generation.     

Entry pathways of herpes simplex virus type 1 into human keratinocytes are dynamin- and cholesterol-dependent

Herpes simplex virus type 1 (HSV-1) can enter cells via endocytic pathways or direct fusion at the plasma membrane depending on the cell line and receptor(s). Most studies into virus entry have used cultured fibroblasts but since keratinocytes represent the primary entry site for HSV-1 infection in its human host, we initiated studies to characterize the entry pathway of HSV-1 into human keratinocytes. Electron microscopy studies visualized free capsids in the cytoplasm and enveloped virus particles in vesicles suggesting viral uptake both by direct fusion at the plasma membrane and by endocytic vesicles. The ratio of the two entry modes differed in primary human keratinocytes and in the keratinocyte cell line HaCaT. Inhibitor studies further support a role for endocytosis during HSV-1 entry. Infection was inhibited by the cholesterol-sequestering drug methyl-β-cyclodextrin, which demonstrates the requirement for host cholesterol during virus entry. Since the dynamin-specific inhibitor dynasore and overexpression of a dominant-negative dynamin mutant blocked infection, we conclude that the entry pathways into keratinocytes are dynamin-mediated. Electron microscopy studies confirmed that virus uptake is completely blocked when the GTPase activity of dynamin is inhibited. Ex vivo infection of murine epidermis that was treated with dynasore further supports the essential role of dynamin during entry into the epithelium. Thus, we conclude that HSV-1 can enter human keratinocytes by alternative entry pathways that require dynamin and host cholesterol.     

Influenza entry pathways in polarized MDCK cells

In non-polarized cell culture models, influenza virus has been shown to enter host cells via multiple endocytic pathways, including classical clathrin-mediated endocytic routes (CME), clathrin- and caveolae-independent routes and macropinocytosis. However, little is known about the entry route of influenza virus in differentiated epithelia, in vivo site of infection for influenza virus. Here, we show that in polarized Madin–Darby canine kidney type II (MDCK II) cells, influenza virus has a specific utilization of the clathrin-mediated endocytic pathway and requires Eps15 for host cell entry.     

Entry of oomycete and fungal effectors into plant and animal host cells

Fungal and oomycete pathogens cause many destructive diseases of plants and important diseases of humans and other animals. Fungal and oomycete plant pathogens secrete numerous effector proteins that can enter inside host cells to condition susceptibility. Until recently it has been unknown if these effectors enter via pathogen-encoded translocons or via pathogen-independent mechanisms. Here we review recent evidence that many fungal and oomycete effectors enter via receptor-mediated endocytosis, and can do so in the absence of the pathogen. Surprisingly, a large number of these effectors utilize cell surface phosphatidyinositol-3-phosphate (PI-3-P) as a receptor, a molecule previously known only inside cells. Binding of effectors to PI-3-P appears to be mediated by the cell entry motif RXLR in oomycetes, and by diverse RXLR-like variants in fungi. PI-3-P appears to be present on the surface of animal cells also, suggesting that it may mediate entry of effectors of fungal and oomycete animal pathogens, for example, RXLR effectors found in the oomycete fish pathogen, Saprolegnia parasitica. Reagents that can block PI-3-P-mediated entry have been identified, suggesting new therapeutic strategies.     

Differences in the susceptibility of five herbivore species and developmental stages to tomato resistance induced by methyl jasmonate treatment

We compared the susceptibility of five herbivores to tomato resistance induced by methyl jasmonate (MeJA) treatment. We tested for lethal effects against five herbivores (Spodoptera litura, Mamestra brassicae, Frankliniella occidentalis, Tetranychus urticae, and Henosepilachna vigintioctopunctata) at various MeJA concentrations. The mortality of all five herbivores increased significantly with increasing MeJA concentration. The 25 % lethal concentration was 0.03 μM for both first-instar larvae of S. litura and third-instar larvae of M. brassicae, 0.51 μM for third-instar larvae of S. litura, 0.76 μM for adult T. urticae, 2.4 μM for first-instar larvae of F. occidentalis, and 5.7 μM for first-instar larvae of H. vigintioctopunctata. Thus, the degree of susceptibility to MeJA-induced resistance of tomato was first-instar larvae of S. litura = third-instar larvae of M. brassicae > third-instar larvae of S. litura ≈ adult T. urticae > first-instar larvae of F. occidentalis > first-instar larvae of H. vigintioctopunctata. Mortality of first-instar larvae of M. brassicae was >90 % at all concentrations. Mortality of fourth-instar larvae of H. vigintioctopunctata (<7 %) was similar to that of the control at all MeJA concentrations. We also detected statistically significant weight loss of the surviving lepidopteran larvae, increased larval duration of F. occidentalis and H. vigintioctopunctata, and reduced egg production by T. urticae grown on MeJA-treated tomato, suggesting that the MeJA-induced resistance can control these herbivores, but effectiveness is different on different species and growth stage. Feeding by both M. brassicae and H. vigintioctopunctata larvae activated JA-inducible genes in tomato.     

Parasitism affects worker size in the Neotropical swarm-founding social wasp, <Emphasis Type="Italic">Polybia paulista</Emphasis> (Hymenoptera,Vespidae)

Summary We discovered two kinds of parasites, i.e., a strepsipteran, possibly Xenos myrapetrus (Trois) and an undescribed gregarine in the Neotropical swarm-founding paper wasp, Polybia paulista (Ihering). Although proportions of workers that were infected by these parasites varied greatly among colonies analyzed, prevalence of infected workers was recognized. Five external characters were measured and compared among uninfected workers, stylopized (i.e., infected by Strepsiptera) workers and workers that were infected by gregarines. Uninfected workers were significantly larger than stylopized workers, while smaller than workers that were infected by gregarines. Nutrients of stylopized workers may be plundered during their growth period, and consequently their body size may be reduced. However, the gregarines may manipulate host larvae to solicit more food from adults or increase development time of larvae longer, and therefore produce more parasites from a larger host.Received 1 July 2003; revised 1 December 2003; accepted 4 December 2003.     

Influenza A virus H5N1 entry into host cells is through clathrin-dependent endocytosis

Influenza A virus H5N1 presents a major threat to human health. The entry of influenza virus into host cells is believed to be mediated by hemagglutinin (HA), a virus surface glycoprotein that can bind terminal sialic acid residues on host cell glycoproteins and glycolipids. In this study, we elucidated the pathways through which H5N1 enters human lung carcinoma cell line A549. We first proved that H5N1 can enter A549 cells via endocytosis, as lysosomotropic agents, such as bafilomycin A1 and chloroquine, can rescue H5N1-induced A549 cell death. By using specific inhibitors, and siRNAs that target the clathrin pathway, we further found that H5N1 could enter A549 cells via clathrin-mediated endocytosis, while inhibitors targeting caveolae-mediated endocytosis could not inhibit H5N1 cell entry. These findings expand our understanding of H5N1 pathogenesis and provide new information for anti-viral drug research. Supported by the National Natural Science Foundation of China (Grant No. 30623009) and National Basic Research Program of China (Grant No. 2005CB523000)