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The closely related species Ixodes persulcatus and I. pavlovskyi are vectors of agents tick-born encephalitis and Lyme disease. These species have two great disjunctive sympatric distribution areas (fig. 1), where both species inhabit the same biotopes, and during the same season. In these conditions there are prerequisites of contacts of opposite sexes of the different species during ambushing the hosts on vegetation. Sequence of "switching on" of the morphological, physiological, and host-parasite factors of reproductive isolation has been established. The features and the range of manifestation of these factors at different combinations of sexes and species of the partners have been revealed. The studied factors, such as precopulative and postcopulative components of the mechanism of reproductive isolation of I. persulcatus and I. pavlovskyi were considered. A hypothesis for sympatric origin of the species as a result of specialization the adults of I. persulcatus to mammals, and I. pavlovskyi to birds is proposed.

We presented the data on the abundance of immature instars of the taiga tick Ixodes persulcatus Schuize on the common shrews Sorex araneus L. in natural foci of tick-borne encephalitis in the south of Western Siberia. Basing on the results of virological and serological studies we demonstrated a low effectiveness of this host species as a donor of disease agent strains, which are predominant in the territory under study, for ticks feeding on shrews. The analysis of samples taken from the young shrews in winter and spring using reverse RNA transcription with polymerase chain reaction and ELISA revealed occurence of subvirion components of the tick-borne encephalitis (RNA and capsid protein E) ether in brain, liver or spleen in 90 percent of shrews (n = 42). Neither hemagglutination antigen nor infectious virus have been detected. We discussed a possible epizootic role of the maintenance of non-infectious tick-borne encephalitis virus in overwintering animals.

Temporal extrapolation prognosis of tick-borne encephalitis diseases in the Primorye territory and its certain regions is made by means of autoregression models. The results obtained shows good prospects of used methods and models.

Maps and dictribution data for six species of the genus Anopheles in Russia are given.

According to the rule of academican E. N. Pavlovskiy, any organism of host is an environment of inhabit for a parasite (Pavlovskiy, 1934). It was analysed, which "ecological niche" or microbiotop (= microhabitat) is occupied by this or that species of symbiotic (parasitic) copepods in organisms. of different groups invertebrate-hosts. The assumption lying in a basis of the given analysis means that each group of hosts may give to cohabitants only certain variants of microbiotopes independently on the general morphological structure and life mode of hosts. Five types of microbiotops offered by various groups of hosts for symbiotic copepods are designated (табл. 2). 1. The body surface of benthic invertebrates as a microbiotope is characterized by conditions being little different (concerning any kind of physical and chemical influences on copepods) from those in external environment on any other substrate. Apparently a trophical dependence plays a determining role in this case. There are certain directions in a development of adaptations, which are characteristic in some extent for all water ectoparasitic crustaceans and have one functional task — to help to an ectoparasite to keep itself on a surface of host body. In the first, the maxillules and maxillipeds significantly are developed, they get a form of large claws, with which the dopepods are strongly attached on a surface of host body and have an apportunity to move on it without a danger to be washed off. In the second, the form of the body undergoes a dorso-ventral expression and expansion of prosome, forms a cephalic shield allowing to the symbiont to press itself tightly to the host body surface and to avoid the loss of host (tab. 2). In occasions, some ectoparasites stimulate the formation of galls in skin tissues of the host, that also provides the parasite with constant conditions, without any threat to lose the host. However, this phenomenon has not a wide distribution and is observed in some groups of crustacean and echinoderm hosts. 2. The narrow tubular cavities in the organism of host either they are a part of external environment (as in channel system of spongia) or a part of internal environment of organism (as channels of blood system or thin parts of a digestive system) have always rigidly limited sizes and form. Characteristics of all parasites occupying this microbiotopes are the strong transformations. They are expressed by the reduction of legs or any other appendages (frequently in a significant degree), loss of segmentation to some extent and in eruciform (or vermiform) form of a body (tab. 2). This microbiotope is occupied by an ectoparasite in one case only (Spongicola uncifer from channel system of spongia) and by endoparasites in all other cases. 3. Large cavities connected with external environment. The formations of various genesis, such as mantle cavity of molluscs, gill cavity and marsupium of crustaceans, bursal cavity of ophiuroids and branchial cavity of ascidians, concern this type of microbiotopes. All of them are characterized by the relative difference from the external environment and rather large volume (in comparison to sizes of copepods), that provides the parasites with a sufficient protection from factors of the external environment and constant source of food such as elements of host body or food's particles brought by the water flow. Morphological changes in inhabitants of the microbiotope have two directions. They practically are absent in the overwhelming majority copepods, living in the mantle of cavity of the lamellibranches. On the other hand, the inhabitants of gill cavity and marsupium of crustaceans, bursal cavities of ophiuroids and branchial cavity of ascidians are characterized by the presence of strong transformations. Usually there are expressed in a loss of segmentation to some extent, reduction of appendages and swelling of body, as in species of the genus Sphaeronella (tab. 2). Changes are also observed in the life cycle: the tendency to reduce stages of development (development of nauplii stage, which takes place under the ovarial cover). In this case the copepodid stages hatch from the ova. 4. The internal cavity of organism of host. This type of microbiotopes in different groups of the hosts is represented in a various degree. We recognise it in a coelome of polychaetes, lacunar system of molluscs, mixocoel of crustaceans, coelome of echinoderms and cavity of body in ascidians. Two basic evolutionary directions are observed in copepods occupying this microbiotope. In the first case, the parasite is not exposed to transformations and keeps the initial plan of structure as in ancestral free-living forms. In the second case the parasites are exposed to strong transformations, they either live directly in cavity's liquid, or are surrounded by a cyst (as in Cucumaricolidae). 5. Microbiotope of the last type is most specific. The simultaneous existence in two environments — external environment (environment of the second order) and internal environment (environment of the first order) leads to the complete loss of ancestral type in a structure and level of organisation. At the same time both morphological and functional division of the parasite body into two parts produces a new formation — the ectosome and endosome. In this case we deals with the phenomenon of mesoparasitism.

The behavioral response of Renicola thaidus cercariae (Renicolidae) to the light has been studied. The positive photo reaction was observed during the first hour of the cercariae free-living period (after shedding from the mollusc). Six hour old cercariae did not show any direct photo reaction. Temporal presence of the positive photo reaction promotes a wider spatial distribution of R. thaidus cercariae. This fact may increases a probability of successful finding and infection of the second intermediate host — bivalves such as the blue mussels. Besides, the more random distribution of infection in bivalve host populations is achieved. This circumstance increases a probability of infected bivalve to be eaten by the final hosts — seabirds.

The seasonal dynamics of the maturation of trematode Bunodera luciopercae was investigated in 1992—1998. The actual fecundity of adult helminths from the ruff, perch, sander and volga pike-perch in the Rybinsk Reservoir was registered in the end of spring. The accumulation process of eggs reflected the host alteration and depended on the food ration, body length and sex of hosts.

The paper provides data concerning the influence of the parasitic worms Aspidogaster conchicola and Bucephalus polymorphus on the rate and duration of ciliary beating of gill and leg in 7 species of Unionidae (Unio conus borysthenicus, U. tumidus falcatulus, U. rostratus rostratus, U. limosus graniger, U. pictorum ponderosus, Colletopterum piscinale falcatum, C. ponderosum rumanicum). The high level of infection of molluscs with B. polymorphus oppresses the glimmeral epithelium activity of gill and leg (by 4.2—32.3%). The weak and moderate levels of infection of molluscs with B. polymorphus do not decrease the glimmeral epithelium activity and sometimes even rise it (by 3.4—8.1%). The presence of few A. conchicola (1—3 individuals) in the organism of mollusc does not change the functioning of glimmeral epithelium.

The results of analysis of phospholipids (PL) and fatty acid content in the blood of sheep infected with the nematodes Dictyocaulus filaria are displayed. A significant increase of lysophosphatidyl-choline and arachidonic acid as well as a decrease of docozagexaenic acid in PL of infected sheep have been recorded. That points out to structural and functional disorders of cellular membranes during the infection. These disorder could be used as a metabolic criterion to estimate the relationships within the host-parasite system examined.

A new cryptobiid flagellates, Cryptobia udonellae sp. n., is described from the excretory channels of Udonella murmanica. The body of flagellates is spindle-shaped. The flagellar pocket is subapical. Two flagella emerge from the pocket. One flagellum turns anterior and is forward-directed; the other flagellum is directed posterior and close to the ventral cell surface. The ventral groove is well developed. The cytostome opens just anterior to the flagellar pocket. The cytostome leads to the short cytopharynx. In the excretory channel of worms the flagellates C. udonellae sp. n. are attached to microvilli of epithelium or lay free in the lumen. Both flagellates have been studied with ТЕМ. The unusual parasite system which involves organisms of four different phylums of animals has been described for the first time.

In experiment, the mean diurnal fecundity of Leptopsylla segnis females increased during the first five days since the beginning of feeding on white mice and reached the maximum in the second five-day period (15.7—16.7 eggs per 1 female during a day). In subsequent period of stay on a host, an activity of egg laying gradually decreased. In flea females, which had lived on hosts for 40 days and more this index was 3.7 eggs. During the mean life longevity (23 days), the flea females lay about 260 eggs; the females, which have lived more than 40 days, produce above 400 eggs.

Two new species of Myxosporidia, Ceratomyxa costata sp. n., and Leptotheca amatea sp. n. from the gall bladder of the Japanese flounder Limanda yokohamae from the Peter the Great Bay are described.

Zoological Institute RAS (up to 1930 — Zoological Museum) dates back to 1728, when the first Russian museum, Kunstkammer, was opened under the authority of the newly organized Russian Academy of Sciences. Zoological collections of Kunstkammer were greatly enriched by a number of naturalists who worked in Russia since the middle of the 18-th century, P. S. Pallas (1741—1811) and I. T. Koelreuther (1733—1806) were among them. Both had made an essential progress into helminthology. In 1895, Zoological Museum legislatively acquired a statute of the central institution in Russia for zoological research. Investigations of parasitic worms here become permanent. First parasitologists in its staff, A. K. Mordvilko (1867—1938) and N. P. Annenkova-Khlopina (1887— 1950), should be mentioned.