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A biodiversity, seasonal dynamics and parasite load of a single individual and local population of the bank vole (Clethrionomys glareolus) were studied in coniferous and mixed forests of the Ilmen-Volkhov lowland (neighborhood of Oskuy village, Chudovo region, Novgorod Province) in the period from June 1999 till May 2002. The Gero's traps were used for collecting the host. Lines of traps stood in each place during 3—5 days and were checked twice a day. Trapping of micromammalian hosts and collecting of parasites took place each month, except a few gaps. Total number of collected animals 2854 including 1405 bank voles. The 29 ectoparasite species were recorded on the bank vole in the area of study. Among some mites and fleas a few species are accidental parasites probably accepted by voles from other species of animals. In the Oskuy area, the bank voles are the main and additional hosts of 25 ectoparasite species: fleas — 8, lice — 1, ixodid ticks — 2, gamasid mites — 7, acariform mites 7. Species composition of ectoparasites, their occurrence and abundance change during the year. Seasonal changes of abundance and occurrence indices are most expressed in the temporary ectoparasites (ixodid ticks, chiggers, gamasid mites), while in the permanent parasites (lice, acariform mites: Myobiidae, Myocoptidae, Listrophoridae), the seasonal fluctuations of indices are displayed in a less scale. Almost vole specimens were infected with this or that ectoparasite species. The parasitocenosis on an individual specimen usually included less than 10 species of the total number 29 species recorded on the bank vole in the area investigated. One ectoparasite species was recorded on 21% of host specimens, 2—5 ectoparasite species were found on 71% of host individuals. Maximal number of ectoparasite species (10 species) was registered on one specimen only. The parasite load was dispersed unevenly among the infected voles. Mean number of parasites of all species on a host individual varied from 124 to 295. The highest grade of parasites (237—297 parasite specimens) was found in the voles with 7—10 species of parasites.

Monitoring studies during 1996—2001 have shown a natural foci of tick-borne borreliosis with high abundance of Ixodes ricinus and high infection rate with an agent: 19.5—38.4 tick individuals per 1 km of route, infection rate 18.0 ± 1.7—22.5 ± 1.5%. A risk to be infected with the Lyme disease in the ricinus focus of the tick-borne borreliosis during the epizootic season did not vary much during the period of study, 3.5—8.2 in different year, mean 6.0 infected ticks per 1 km of route.

A morphometric analysis of different male and female organs used in the process of copulation, including an attachment of the spermatophore to the genital opening of female and placing the spermatophore into the vestibular part of vagina, was carried out for the pairs of ixodid tick species Ixodes persulcatus — I. pavlovskyi and I. persulcatus — I. ricinus in areas of their sympatry. In two disjunctive areas of sympatry of I. persulcatus — I. pavlovskyi (South-East Altai and Southern Primorye), the morphological barrier is displayed in the precopulation mechanism of reproductive isolation and does act only in the pair I. pavlovskyi female — I. persulcatus male. It is proved by the reliable prevalence of the hypostome diameter (in widest part) of I. persulcatus male over the genital opening length of I. pavlovskyi female. Because of this reason, the copulation between these partners cannot take place. On the other hand, there are no any morphological obstacles for a copulation within each species examined and in the combination I. persulcatus female — I. pavlovskyi male, and in any combination of the partners I. persulcatus — I. ricinus in sympatry areas (samples from two locations in the north-west of the Eastern-European Plane have been examined). Morphological peculiarities causing differences in host preference of tick species, that in turn realizes the isolation mechanisms between species, are discussed. Postcopulation non-genetic components of the reproductive isolation mechanism have been found in examined species.

Daughter sporocysts of Sanguinicola armata are represented by several generations, changes of which goes synchronously with the changes of year seasons. Young individuals beginning the reproductions form exclusively cercariae. The old sporocysts begin to produce sporocysts only. These young sporocysts do not quit the organism of the old sporocyst. Therefore, series of sporocysts inside other sporocysts are often observed in hystological cross-sections. Germinal masses of daughter sporocysts of S. armata have some specific characters, which are not observed in analogous organs in daughter sporocysts of other trematode species.

Three parasitic systems of Microsporidia are described: the system of monoxenic Vairimorpha mesnili with paraxenic hosts presented lepidopteran and hymenopteran species; the system of dixenic Amblyospora sp. with metaxenic hosts presented bloodsucking mosquitoes and crustaceans and the system of Metchnikovella sp. as parasite of other obligate parasite. The last case is characterized by very intimate interrelations between hyperparasite (microspori-dian species), obligate parasite — host of Microsporidia (gregarine) and hyperhost — host of gregarine (polychaeta). This hyperparasite system is exclusive case of parasitic systems. Parasitic and hyperparasitic systems reflects a population level of host-parasite interactions. On biocenotic level many other organisms such as predators, vectors and reservators of invasion stages of Microsporidia affect parasitic systems giving a chance to one of the members of the system (to the host or to the parasite). These organisms form epiparasitic system. In all cases of the parasitic systems there are two-way communications between parasites and their hosts. In systems on biocenotic level — parasitic consortium — members of epiparasitic systems acts on parasitic systems, but members of parasitic systems don't affect epiparasitic systems.

A long adaptation of Microsporidia to intracellular development supposes the host-derived ATP dependence of merogony and sporogony stages. To prove this assumption the activities of ten carbohydrate and energy metabolism enzymes were compared in the microsporidia Nosema grylli intracellular stages and mature spores. This species infects the fat body of crickets Gryllus bimaculatus. We have demonstrated lower activities of glycolytic enzymes, phosphoglucomutase and glucose-6-PhDH in the metabolically active meronts and sporonts than in the dormant mature spores. Low glycolysis level indicates that carbohydrate catabolism is not a principal mechanism of ATP supply in the N. grylli intracellular stages. Furthermore, we have not revealed a preferable expenditure of glycogen in comparison with triglycerides in infected cricket fat bodies. The N. grylli infection causes an equal reduction of glycogen and lipid content approximately in 2—3 times. Microsporidia have not mitochondria, Krebs cycle and electron-transport chain. Therefore they are not able to utilise fat reserves for ATP production. It seems to be proposed that microsporidia consume exogenous ATP which is produced by host cell metabolic system. The N. grylli infection provokes an increase of ATP content and ratio of ATP/ADP concentrations in cricket fat bodies approximately in 4 times. These data indicates a rise of host cell energy metabolism rate during the infection.

Data on 13 species of fish myxosporeans from the Antarctic part of the Atlantic Ocean is present. Among them, 8 new species are described: Zschokkella australis sp. n., Davisia nototheniae sp. n., Ceratomyxa orthospora sp. n., С. ellipsoidea sp. n., С. antarctica sp. n., Leptotheca ampla sp. n., Pseudalataspora squamifrons sp. n., P. meridionalis sp. n. Four species were found for the first time in the region and four species were found in new hosts.

The Bradophila pigmaea Levinsen, 1878 is redescribed on the basis of new material collected firstly after original description. The new family Bradophilidae belonging to order Poecilostomatoida is erected on the basis the genus Bradophila. The male of Bradophyla pigmaea is described in detail at firstly.

Summary is absent.