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For 70 years of the development of concept of the natural nidality of human diseases many its initial postulates undergo considerable changes, while its essence remain the same. Many "new" infections with natural foci were discovered and their geographic distribution was investigated in detail, classification of natural foci was developed. It was established, that epidemic features of transmissive infections depend mainly on the types of parasitism of their insect, tick and mite vectors.

Unique features of the collection of ixodoid ticks in the Zoological Institute of Russian Academy of Sciences (St. Petersburg, Russia) are characterized. The collection is stand out against a background of other world's collections by the presence of complete geographic series from whole ranges of species, including all active stages of ontogenesis. The results of basic and applied investigations obtained owing to the characteristics of this collection are summarized briefly. The contribution to the taxonomic investigations of ixodoid ticks connected with the problem of natural foci, based on the collection, is analyzed. Urgent directions of ongoing and future studies based on the collection are considered.

We studied two urban and two suburban biotypes of Tomsk City for tick-transmitted diseases prevalence in naturally collected ticks. Tick-borne encephalitis virus (TBEV) was found in 6.5% of tick samples, West Nile virus (WNV) in 2.2%, Borrelia spp. in 8%, Rickettsia spp. in 2.5%, and Ehrlichia spp. in 1.7% of samples. Genetic markers of Powassan virus, Bartonella spp., and Balbesia spp. were not found. Analysis of the genetic diversity of revealed pathogens resulted in the following conclusions: 1. TBEV strains belong to Siberian and Far-Eastern subtypes, and Far-Eastern subtype of TBEV is most frequent in urban biotypes (up to 43% of urban strains of TBEV); 2. WNV strains belong to genotype la; 3. Borrelia spp. were classified as B. garinii; 4. Rickettsia spp. were classified as R. tarasevichiae and probably as a new Rickettsia raoultii subspecies; 5. Ehrlichia spp. were classified as E. muris. The coexistence of several pathogens was found in 5.7% of tick samples, and the most frequent combination was TBEV + Borrelia spp.

Significance of 3D-shape investigation of the mosquitoes male genitalia is shown by an example of species from the genus Aedes (Diptera, Culicidae). Differences between true 3D-shape of the male genitalia and traditional 2D pictures made as a result of the examination of balsam microscopic slides are revealed. Original descriptions of 3D-shape of coxites, claspettes, 9th tergal lobes, and proctiger of 30 species from the subgenus Ochlerotatus have allowed us to find new diagnostic characters, namely general 3D-shape of basal lobe of coxite, claspette filament, and some other structures.

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.

Interrelation of parasitological and epidemiological estimations of potential danger of different territories Primorsky Krai concerning presence of natural foci of tick-borne diseases is discussed. Comparative analysis of long-term dynamics of the tick-borne diseases' sickness rate in comparison with long-term dynamics of the vector ticks' abundance has been carried out.