[Abundance of larvae and nymphs of the taiga tick Ixodes persuicatus (Acari: Ixodidae) on small mammals in the cut-over lands of the middle taiga subzone of Karelia].

Data of long-term investigations (1998-2004) on the abundance of the taiga tick larvae and nymphs in the cut-over lands of different age in the middle taiga subzone of Karelia (62 degrees 04'S; 33 degrees 55'W) are presented. The investigation was carried out on three model cut-over lands of different age: 1) "young" cut-over land; age of cut-over in the beginning of investigation is 7 years; Betula-Deschampsia cespitosa-Agrostis tenuis; 2) "middle" cut-over land; age of cut-over is 12 years; Salix-Deschampsia cespitosa-Agrostis tenuis; 3) "old" cut-over land; age of cut-over 25 years; Alnus incana-Rubus idaeus-grass. The number of ticks was estimated by using common parasitological indices: prevalence, abundance, and index of feeding intensity (the tick abundance multiply by the number of small mammals per hundred traps-nights). In the beginning of investigation the "young" cut-over land was a typical meadow association. The lowest tick abundance was recorded here. That was a result of unfavorable abiotic conditions and low number of small mammals in the beginning of summer. "Middle" cut-over land is characterized by the highest number of the tick larvae, which is the evidence for high number of the hosts of tick imago. "Old" cut-over land has the optimum conditions for development of taiga ticks. High abundance of the ticks (larvae and nymphs) was recorded during the whole period of investigations. The number of preimaginal ticks is shown to be much higher in cut-over lands as compared with that in mixed and coniferous forests, due to the higher number of small mammals.

[Dynamics of the helminth fauna in the common shrew (Sorex araneus L.) from cut-over lands of different age in Karelia].

Species diversity of helminths in the common shrew from three cut-over lands of different age in Karelia was studied. It was shown, that change of the plant cover in cut-over lands have no a significant effect on the species diversity of helminth communities in Sorex araneus, but the abundance of individual parasite species changes considerably. Changes of the S. araneus infestation with helminths were the greatest in a new cut-over land. Structure of the helminth community comprises four categories of parasites (dominants--4 species, subdominants--8, rare species--13, very rare species--10) and depends on the time passed since the felling. A redistribution of the species constituting the core of the helminth fauna was to be observed. It was shown, that being an integrated indicator of the status of terrestrial ecosystems, parasites clearly indicate changes not in the structure, but in the abundance and domination of individual species of terrestrial invertebrates and vertebrates in cut-over lands.

[Patterns of host-parasite interactions between the nematode Heligmosomum mixtum (Schulz, 1952) and the bank vole (Clethrionomys glareolus Schreber, 1780)].

Some aspects of the host-parasite interaction of the nematode Heligmosomum mixtum and the bank vole have been studied. The dependence of infestation on the host sex, age and weight, the seasonal and annual abundance dynamics are investigated. It has been found that the bank vole is the main host of H. mixtum; the distribution of H. mixtum abundances in the host population is described by a negative binomial distribution model. The greatest infestation is characteristic for mature bank voles; males are infected more heavily than females. Infestation with the nematode increases alongside with the host weight. Seasonal dynamics of the nematode abundance in a bank vole population appears as a curve with a maximum in January and a minimum in August; the infestation curve for 1-month-old animals captured from June through October has two peaks (in July and October), with a minimum in June. The number of parasites in the ecosystem over a long-term period changed synchronously with the host abundance. The synchronism in the host-parasite system dynamics is possible when the parasite has a short life span, and does not influence the host abundance.

[The helminth fauna of the shrew genus Sorex (Insectivora: Soricidae) in the Kandalksha nature reserve].

The helminth fauna of shrews (Sores araneus, S. caecutiens, S. minutus, S. minutissimus) from the Karelian coast and islands of the Kandalaksha nature reserve was studied. 18 helminth species belonging to 3 taxonomic groups, Trematoda (3), Cestoda (8), and Nematoda (7) were found. The main body of the helminth fauna of shrews is represented by the nematodes species Longistriata codrus, L. didas, and the cestode species Ditestolepis diaphana. Inhabiting of shrews in the insular localities leads to the decrease of the species diversity and the abundance of their helminths. The distribution ranges of the shrew parasites have been outlined more accurately.

[Biotope distribution of cestodes from the common shrew Sorex araneus in southern Karelia]. / Osobennosti biotopicheskogo raspredeleniia tsestod obyknovennoi burozubki (Sorex araneus L.) Iuzhnoi Karelii.

Specific features in the formation of cestode species composition in the common shrew in different biotopes have been analyzed. Four categories of parasites have been recognized depending on a degree of dominance: dominants (Neoskrjabinolepis singularis, Molluscotaenia crassiscolex), subdominants (Ditestolepis diaphana), adominants A (Staphylocystis furcata, Vigisolepis spinulosa, adominants B (Hymenolepis scutigera, Dilepis undula, D. secunda, Taenia mustelae). A significant similarity was discovered between the species diversity and the dominance characteristics of cestodes. It was found that the distribution of mass species of parasites in the host population corresponds to the gamma distribution model. In regard to cestodes examined, a hypothesis considering the spatial structure and size of territory occupied by stable parasitic system is put forward.

[Parasite-host relations in toxascariasis in Arctic foxes]. / Parazito-khoziainnye otnosheniia pri toksaskaridoze pestsov.

The effect of host infection doze (10, 100, 1000 eggs) and developmental stages of helminths (larvae, adult nematodes) on the relationships in the system "Toxascaris leonina-Alopex lagopus" was studied experimentally. It has been established that 100 eggs are the threshold dose for helminths and 1000 eggs for the host. More distinct changes in the indices are characteristic of the parasite. Dynamics of host-parasite relationships in the development of the parasitic process correspond to helminth developmental stage. Larvae of T. leonina are most pathogenic for the host.