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The history of studies of the biological age in ixodid ticks is discussed. A method of estimation of the biological age in adult ticks of the genus Ixodes by the degree of fat inclusions in midgut cells and in the fat body is developed. An "age scale" for the determination of the calendar age was assumed.

The age structure of I. pavlovskyi natural populations from Novosibirsk and its outskirts was studied with the use of the fat reserves in the midgut and in the fat body as the age index.

Some criteria for the estimation of the biological and calendar age by the fat storage in midgut cells of Ixodes persulcatus males were established on the basis of examination of ticks from the laboratory culture.

PCR identification of host DNA in unfed females and males of taiga tick Ixodes persulcatus was performed. Amplification of each sample was done using primers species-specific by 12S rDNA mitochondrial gene. Four species of small mammals (Apodemus uralensis, Clethrionomys glareolus, Microtus arvalis, and Sorex araneus) and two passeriform bird species (Fringilla coelebs and Parus major) were analysed. For one third of tick samples, hosts of previous stages were established using this method. In five cases, feeding on more than one host species was detected.

Formalin fixation is proved to be the useful tool in the method of age estimation for the taiga ticks collected in field. Formalin does not deform fixed material and does not dissolve fat; hence, it is the best fixing fluid when tick age is estimated by the state of fat reserves in its organism. The ticks preserved in 9% formalin were shown to be suitable for age estimation 1.5-2 months after fixation.

The method of estimation of the biological age in non-feeding tick females by the level of adipose inclusions in the cells of the midgut and fat body is developed. In order to estimate the fat reserves in non-feeding females, alive ticks were dissected and fragments of their internal were vitally stained with the pregnant solution of sudan III in 70 % ethanol. Three age-specific groups were established: I, young females whose intestines and fat body were filled with fat inclusions; II, mature females whose fat reserves were partially expended; III, old females having isolated fat inclusions in their midgut and fat body.

A method of visual estimation of the biological age of living hungry tick females by visible changes in the depth of marginal groove and the structure of the alloscutum cuticle during natural ageing is developed. In recently activated individuals, the body is convex and the marginal groove is exposed, demonstrating distinctly visible cuticular microfolds (Figs 1-4). In attenuated ticks, the body is flattened and marginal fold overlays the marginal groove, concealing cuticular microfolds (Figs 5-8).

Morphofunctional investigations of five Ixodes species (Ixodes pacificus, I. pavlovsky, I. persulcatus, I. ricinus and I. scapularis) were carried out. It was established, that the change of midgut epithelium lags at the each next developmental stage, and it is not synchronized with general processes of metamorphosis and organogenesis during molts. The midgut epithelium of a previous phase of the life cycle persists and functions during the feeding stage at the next phase.

The paper reports the results of eight-year investigations on the ectoparasites of rodents and insectivores carried out in southern taiga of the Ilmen-Volkhov lowland (Novgorod Region) and Kurgolovsky reserve (Leningrad Region). Twelve species of small mammals were captured including three dominate species--bank vole Clethrionomys glareolus (2722 specimens), common shrew Sorex araneus (1658 specimens), and wood mouse Apodemus uralensis (367 specimens). Parasite community of the bank vole comprises 34 species of mites, ticks, and insects, the community of common shrew comprises 25 species, and the community of A. uralensis includes 28 species. Taxonomic diversity of the ectoparasite communities was shown to be based on the diversity of types of parasitism and ecological nishes of the host body. Permanent ectoparasites are found to be represented by 2 species of lie and 14 species of acariform mites. The group of temporary parasites includes 13 species of fleas, 10 species of gamasid mites. 3 ixodid species and 1 Trombiculidae. There is a common pool of temporary parasites of small mammals in the ecological system of taiga. Significance of different shrew and rodent species as hosts were found to be dependent on the population density in possible hosts and many other factors. Species diversity in the parasite communities of different small mammal species is dependent on the number of possible ecological nishes in the host body. Actual infill of these nishes by ectoparasites is usually lesser than potential one. Species composition of temporary parasites, their occurrence and abundance changes according to season. Interspecific competition in the temporary parasite species can decrease because of the seasonal disjunction of their population peaks. Diversification of the ecological niches of ectoparasites allow simultaneous feeding of more parasite individuals on one host, than in the case of parasitising of single species or several species with similar ecological nishes. The distribution of parasites on their hosts was also studied. The aggregative distribution has been found in ixodid larvae only, and the distribution of fleas was close to the Poisson distribution. Deviations from the aggregative distribution can be an effect of several independent factors, including limited ability of small mammals for providing numerous parasites with food. On the most part of hosts simultaneous parasitizing of no more than 1-3 individuals of each tick, mite, and flea species was registered. Excessive infestation by ectoparasites may probably be limited by effective reactions of self-purification in the mammal hosts.

Histopathology in the sites of localization and parasiting of the mites Psorergates apodemi Fain et al., 1966 and P. dissimilis Fain et al., 1966 on the Ural field mouse Apodemus uralensis (Pallas) and the bank vole Clethrionomys glareolus (Schreber) is described. The mites affected all epidermis cell layers down to the cambium layer and caused hyperkeratosis.

Changes in the midgut of the Ixodes ricinus nymphs at the stage of developmental diapause were studied. It is established, that the midgut of the tick nymphs undergoes the identical and synchronous changes at the development without diapause and in the state of diapause. In 7-8 months after feeding the midgut of the nymphs containes the digestive cells with gematine and food inclusions, as well as reserve cells, like the midgut of unengorged moulted female. But the midgut of diapausing nymphs retaines such condition during the whole period of diapause.

The changes of the midgut in the females of the tick species Ixodes persulcatus and I. ricinus during the second and third immunizing feeding on rabbits were studied by the histological technics. The alternation of one generation of the digestive cells of nymphal stage and two generations of the digestive cells of adult stage was observed. The generation of secretory cells is absent. The tick completes feeding and drop off when the last generation of the digestive cells is on the initial activity stages. The amount of the blood consumed is not enough for the rhythmical functioning of the midgut. The feeding of tick is broken on the second phase and full satiation does not take place. It is apparently an effect of the interruption of the blood entrance into the midgut cavity of feeding tick as a probable result of anti-ticks resistance of unnatural hosts.

The midgut epithelium of the virgin females in Ixodes ricinus, L. pacificus, and I. persulcatus is represented by the digestive cells of nymphal phase and stem cells. Digestion of feed is performed by the one generation of digestive cells of nymphal phase and two generations of digestive cells of adult females. The generation of secretory cells and two generations of digestive cells are absent. The feeding of virgin females is not completed but interrupted in the second phase during the period of slow feeding and preparation of the intestine for the third phase.

The midgut epithelium of feeding nymph is represented by the digestive cells of larval phase. Digestion of the main part of feed is performed by the one generation of digestive cells of nymphal phase after detachment, during moult. This period precedes the apolysis. The generation of secretory cells is absent on the nymphal phase. Secretory vacuoles are formed in the digestive cells of larval phase. All functioning cells form a peritrophic matrix on their apical surface. The replacement of the digestive cells of larval phase by the digestive cells of nymphal phase proceeds gradually, during the first 5-10 days after detachment. The beginning of the accumulation of digestive inclusions in the young digestive cells of nymphal phase takes place in the 10-15 days after detachment.

The formation of the peritrophic matrix in the midgut of females of 5 ixodid tick species (Ixodes pacificus, I. pavlovskyi, I. persulcatus, I. ricinus and I. scapularis) was studied by means of light and electron microscopy in different periods of the feeding and after detachment. The formation of the peritrophic matrix started when the first food portions came into the gut lumen, 9-12 hours after the attachment. Renovation of the peritrophic matrix took place during the whole feeding period; every new generation of midgut cells synthesized their own matrix. It was deposited on the apical surface of every midgut cell in the beginning of differentiation, and was functioning during the life of the cell. The peritrophic matrix separates spaces of the cavitary and cytozoic digestions.

Cyclic changes of the midgut epithelium were observed in females of 5 ticks species of the genus Ixodes during 7-10 days of feeding. The midgut epithelium of unfed females is represented by the digestive cells of nymphal phase and stem cells. The digestive cells of nymphal phase are functional during 1.5-2 days after attachment of the tick, and then, after the tearing away they go into the gut lumen. The secretory cells substitute the digestive cells of nymphal phase and finish their growth during the 4-4.5 days. Secretion of digestive enzymes is performed by the holocrine type with tearing away a whole cell. Intracellular digestion takes place in the digestive cells of four consequent generations. The secretory and digestive cells form a peritrophic matrix on their surface. The presence of peritrophic matrix gives an evidence the maturity and functional activity of the secretory and digestive cells. We suggest, that the peritrophic matrix takes part in intracellular digestion, namely in the process of micropinocytosis. The phagocytosis was not found in the ticks investigated. Digestion in the midgut lumen is performed by enzymes of the ruptured secretory and digestive cells, that is proved by the haemolysis of erythrocytes in the zone of their contact with these cells. The digestive cells of each generation functioned almost synchronously, with largest difference in starting about 12 hours.

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. Most 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.

Histopathological changes in a skin of Lacerta agilis in the places of attachment and feeding of nymphs of Ixodes pacificus and I. ricinus were investigated. The mouthparts of ticks are surrounded by the fibrin cone and collagen capsula formed by their hosts. Ticks of these species do not produce the cement. A proliferation stage of skin inflammation is expressed, the large collagen capsula is formed as the result of proliferation. Neutrophils and eosinophils predominate in the inflammate cell infiltrate.

Histopathological changes of skin of Passeriformes birds in the places of attachment and feeding of the Ixodes persulcatus and I. lividus were investigated. The inflammation of bird skin is analogous to one of mammalian skin. The mouthparts of tick are surrounded by the fibrin cone and collagen capsula. They are formed by host. Ticks of these species do not form the cement. A proliferation stage of skin inflammation in birds is expressed. The thick collagen capsula develops in a result of proliferation. The feeding cavity is formed by the process of sucking a blood, inflammate cell infiltrate and products of tissue lysis. Neutrophils and eosinophils predominate in the inflammate cell infiltrate.

Histopathological changes in the places of attachment and feeding of the Ixodes trianguliceps, I. persulcatus, and I. ricinus on natural hosts are similar. They pass through the stages of skin inflammation: perforation, exudation and proliferation. The mouthparts of tick contact with the host tissues. The fibrin deposit and callogen capsule surround the mouthparts. These species of ticks do not form the cement. Formation of the feeding cavity is caused by the salivation of ticks and neutrophil infiltration into surrounding tissues. Unnatural hosts (mice, rabbits) do not form the callogen capsule in the places of feeding, the callogen fibres are disposed irregular. Mast cells accumulate in the tick attachment site in the skin of natural host and degranulate in response to the tick salivary antigens releasing the histamine. Mediators involve cutaneous hypersensitivity reactions.

The borreliosis etiology was verified in 60% cases of the morphea, 100% cases of the atrophoderma of Pasini-Pierini and 100% cases of anetoderma by means of IFA with Ip-21 antigen (B. afzelii) and silver staining after Levadity. Borreliae were located near the capillaries, muscular and areolar tissue fibers of the derm and near the granulated cells of epidermis.

Three generations of the taiga tick Ixodes persulcatus, the descendants from naturally infected females, have been examined by means of dark field and phase contrast microscopies and indirect immunofluorescent reactions with monoclonal antibodies. Location of borreliae in oocytes was examined by means of electron microscopy. The examined ticks derived from 9 females collected in the Novgorod Province, from 6 females of 1st laboratory generation and 5 females of the 2nd generation. In total, 250 larvae, 178 nymphs, 59 females and 70 males of three consequent generation have been examined. Almost 100% of descendants of naturally infected females were infected with Borrelia burgdorferi s. l. and similar infection rate was observed in unfed tick larvae collected in field conditions. The borreliae received transovarially to larvae of the 1st generation then were transmitted to 100% nymphs and imago of this generation and two next generations.

Mammals and ticks was collected in 1995-1997 years in Novgorod region from May to September. Traps were exposed during 5 consecutive days every month in 4 different biotopes. 928 hosts were captured during three years. 357 larvae and 59 nymphs of Ixodes persulcatus, 356 larvae and 71 nymphs of I. trianguliceps were collected. The Clethrionomys glareolus and Sorex araneus are main hosts of larvae of I. persulcatus and I. trianguliceps. C. glareolus feed 76.2% of I. persulcatus larvae and 25% of I. trianguliceps larvae, S. araneus--27.1 and 45.9% of larvae, respectively. The abundance of larvae and nymphs of I. persulcatus was 0.26 and 0.13 on C. glareolus, and 0.41, 0.08 on S. araneus; for I. trianguliceps this indices are 0.15 and 0.09, 0.95 and 0.13, respectively. Infection rate of larvae and nymphs I. persulcatus and I. trianguliceps with Borrelia burgdorferi s. l. was 94-100%, confirmed by IFA with H5332. The borreliemia was found in 13.6% G. glareolus, 6.6--Microtus arvialis, 4.2% Apodemus uralensis. For all species of sorex this index varied from 0.9 to 44.9% in different years. Increase of mammal's numbers with the borreliemia correlated with peaks of activity of larvae of I. persulcatus. Finding of Borrelia burgdorferi s. l. in I. trianguliceps indicates an occurrence of enzootic locuses.

Borrelia burgdorferi s. lato have been recovered by means of an observations in a dark screen, phase and anoptrail contrasts in 87.47% imago and 100% nymphs and larvae of the Ixodes persulcatus ticks collected in the Leningrad, Novgorod and Pskov regions. Four morphological types of borreliae have been recognized, which were present in all stages of ticks examined. The location of the agent in ticks was examined in the material coloured after Levaditi. In the hungry stages and the most abundance of the agent was accumulated at the apical surface of midgut epithelium. In the majority of hungry I. persulcatus the generalized infection was recorded. The feeding stimulates the migration of the agent through the intracellular space to the basal membrane and cells of organs and finally leads to complication of the agent in the organism of vector.

The borreliemia was discovered in 22 (44.9%) of 49 common shrews (Sorex araneus, Soricidae), which were captured in the end of July-August 1995 in the Novgorod Province. The borreliae were located near the capillaries of the true skin and in the veins of the subcutaneous layer.

The borreliosis of laboratorian rabbits displays as a chronic infection with recurrences during a spring-autumn season. The clinical picture includes a skin-ulcerous lesion, arthritis accompanied by lymphocytosis and borreliemia.

The direct correlative dependence between indices of absolute and relative number of two fly species calculated by Peterson's method is shown. The way of calculation of the absolute number of M. domestica and S. calcitrans and the receipt of the selection from subpopulations, which take in account peculiarities of adult fly distribution in different technological regimes of cattle keeping, peculiarities of daily activity and influence of temperature-photo factors on imago, are proposed. The attempt to study the structure and density of subpopulation of two fly species during one generation in North-West Russia is made. The date on mortality on different stage of life cycle are given.

In order to estimate the absolute number of Stomoxys calcitrans subpopulation in housings of a dairy farm the capture-mark-recapture method has been used. It has been established that the absolute number of S. calcitrans subpopulation can be as high as 100,000 specimens per a farmyard. The possibilities of using indices of the relative number of flies (caught on fly-paper) for estimation of the absolute number of these insects in the housings of farms have been found out.