Veronika Michalková

Eugregarine trophozoite detachment from the host epithelium via epimerite retraction: Fiction or fact?

Eugregarines represent a diverse group of Apicomplexa parasitising numerous invertebrates. Their sporozoites generally develop into epicellular trophozoites attached to the host epithelium by a specialised attachment organelle known as an epimerite. They are considered peculiar protists due to their unique cell architecture and dimensions as well as their attachment strategy which is similar to that of cryptosporidia. Using electron and fluorescence microscopy, the fine structure of the epimerite with associated structures and the mechanism of trophozoite detachment from the host epithelium were studied in Gregarina polymorpha parasitising the intestine of Tenebrio molitor larvae. The epimerite appears to be a very dynamic structure whose shape dramatically changes depending on whether or not it is embedded into the host epithelium. The trophozoites most fragile zone is the area below the membrane fusion site at the epimerite base. The epimerite plasma membrane forms basal radial ribs which are involved in increasing its surface and strengthening the epimerite-host cell junction. FITC-phalloidin labelling demonstrated the presence of filamentous actin in trophozoites along with its accumulation at the epimerite base and in the apical end of the protomerite, as well as a patch accumulation of filamentous actin in the protomerite of maturing and mature trophozoites. Indirect immunofluorescence revealed the presence of myosin in the cortical zone of the epimerite and in the membrane fusion site area. The data obtained strongly suggest that these structures could facilitate the detachment of a mature trophozoite from the host epithelium. Supported by data presented herein and our previous observations, we propose a new hypothesis on the mechanism of trophozoite detachment from the host epithelium based on epimerite retraction into the protomerite. This is contrary to the commonly accepted hypothesis describing gradual epimerite constriction and subsequent separation facilitated by contractility of the membrane fusion site (osmiophilic ring).

Larval Morphology and Anatomy of the Parasitoid Exorista larvarum (Diptera: Tachinidae), with an Emphasis on Cephalopharyngeal Skeleton and Digestive Tract

Abstract The endogenous development of the tachinid gregarious larval parasitoid Exorista larvarum L. (Diptera: Tachinidae) has been analyzed in the last larval instar of a factitious host, the wax moth Galleria mellonella L. (Lepidoptera: Pyralidae), with the use of histological techniques and scanning electron microscopy. This study has focused on the parasitoid internal body structures and their changes during the larval development. The first and second instars are enveloped by a host-derived hemocyte capsule attached to the respiratory funnel via a prominent anal hook located between 2 anal lobes. The third instar abandons the respiratory funnel and migrates free in the body cavity of the already dead host. Emphasis is given to the prominent cephalopharyngeal skeleton, highlighting the morphological aspects of its sclerotized as well as non-sclerotized components. In addition to the cephalopharyngeal skeleton, the anterior third of the larval parasitoid body is occupied by large salivary glands, massive proventriculus, and cerebral ganglia. The extensive digestive tract, which occupies the major part of the body, is differentiated into well-marked individual parts. The abdomen is predominantly filled with the extremely long mesenteron that increases in size during the larval development. The whole body is covered by an apparently thin integument, with strong spines that are especially numerous in the anterior and posterior body parts.

Temporal effects on host-parasite associations in four naturalized goby species living in sympatry

Introduced host species are often characterised by reduced parasite numbers compared to their native populations. Any such advantage gained from parasite release following introduction into a new area may often diminish over a short period as the new host gradually acquires local parasites. In this study, the metazoan parasite communities of four goby species (Proterorhinus semilunaris, Ponticola kessleri, Neogobius melanostomus, and Neogobius fluviatilis) recently introduced into the lower River Rhine were investigated. Mean parasite abundance and infracommunity richness were positively associated with time since host introduction, both parasite variables being the highest in P. semilunaris. In Ponticola and Neogobius species, parasite species richness and the dominance of larval parasites in the Lower Rhine were similar to that for non-native populations in the middle Danube. Sporadic local parasite acquisition and infection, predominantly by species commonly found in the native range, led to a relatively high qualitative similarity in parasite communities between hosts. The relationship between parasite abundance and fish size reflected size-dependant food selectivity and/or parasite accumulation throughout the host’s life. Data from this study emphasise the importance of duration of co-occurrence, host habitat and foraging preference, as well as the co-introduction of suitable intermediate hosts, for parasite community composition in related species.

On the pathogens of the spruce bark beetle Ips typographus (Coleoptera: Scolytinae) in the Western Carpathians

Pathogens of spruce bark beetle Ips typographus were compared at eleven sites in Slovakia (the Western Carpathians). Seven different pathogen species were recorded: protozoan species Chytridiopsis typographi, Gregarina typographi, Malamoeba scolyti, nematodes of the genus Neoparasitylenchus and one unidentified nematode species. Presence of the entomopathogenic fungus Beauveria bassiana was also observed as well as parasitization by hymenopteran parasitoids. High infection rate of G. typographi and the nematode Neoparasitylenchus was detected in almost all sites and lethal impact of M. scolyti by massive infections was observed. The beetles from seven sites were screened for endosymbiotic bacteria Wolbachia, however, with no positive result.

Penetration and encapsulation of the larval endoparasitoid Exorista larvarum (Diptera: Tachinidae) in the factitious host Galleria mellonella (Lepidoptera: Pyralidae)

The tachinid fly Exorista larvarum (L.) (Diptera: Tachinidae) is a polyphagous larval endoparasitoid that deposits its eggs on the host exoskeleton of lepidopteran and tenthredinid larvae. The attachment of larval E. larvarum and the formation of the respiratory funnel were studied during infestation in the last larval instar of the wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae). The tachinid larvae burrow through the host integument after hatching, using their robust cephalopharyngeal skeleton, leaving a dark spot at the point of their penetration as a result of host cuticle melanization. Endoparasitoid penetration induces the host cellular defence, resulting in the formation of a haemocyte capsule consisting of multi-cellular sheaths. This enveloping capsule later undergoes melanization, which is mostly obvious towards the posterior part of the endoparasitoid. The endoparasitoid uses the host encapsulation response to build a respiratory funnel from the modified host integument, leading to the host surface. The encapsulated larva remains attached to the respiratory funnel via an anal hook and cuticular spines until fully developed. Additional immunohistochemical analyses were used to study host-parasitoid interactions. Indirect immunofluorescence showed no labelling of potential tachinid antigens and confirmed no effect on the surrounding host tissues. A simulated parasitization with coated polybead microspheres revealed the mortal impact of tachinid antigens to the host. Hosts injected with antigen-coated polybeads died as a consequence of an acute and extensive immunological response to the tachinid antigens and not due to the trauma caused by foreign objects inside their body.

Experimental evidence for parasite-induced over-winter mortality in juvenile Rhodeus amarus

In this study, the effects of the eye fluke Diplostomum pseudospathaceum (Trematoda) infection on over-winter survival of young-of-the-year (YOY) European bitterling Rhodeus amarus (Cyprinidae) were examined between September 2010 and April 2011. The fish were reared in semi-natural conditions to ensure that results were not confounded by other parasite infections. The cumulative mortality of R. amarus from November until April was significantly higher in D. pseudospathaceum-infected fish (57·3%) compared to controls (42·1%). Infection of the parental generation did not have any effect on the mortality of juveniles. The results indicate that D. pseudospathaceum infection increases over-winter mortality of YOY R. amarus. The possible mechanisms causing mortality are discussed.