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Analysis of long-term data on the infection rated of the taxonomic complex Borrelia burgdorferi s. l. in Ixodes persulcatus and I. ricinus from Moscow Region is carried out. More than 14 000 tick specimens were examined by dark-field microscopy and 704 specimens were investigated by PCR. Two borrelia genospicies, B. afzelii (63%) and B. garinii (20%) proved the most prevalent. The genospecies could form a mixtinfection (11%). Borrelia miyamotoi, B. valaisiana, and B. burgdorferi s. s. were also found in the studied territory, with the total ratio lesser than 6%. Acarotropism of Borrelia proved 2.4 times higher with respect to I. persulcatus, than to I. ricinus. Average long-term infection rates of these tick species were 27.3 and 11.3% respectively. Spatial variability of the infection rate in ticks significantly exceeds interannual fluctuations with the variation coefficients 66 and 26% respectively.

Synonymy of the genera, subgenera, and species of the family Culicidae Meigen, 1818 from Russia is revised. More than 300 synonyms for 9 genera, 23 subgenera, and 105 species of mosquitoes are listed.

The new species of virgulate cercariae, Cercaria agstaphensis 6 and C. agstaphensis 14, were described from the freshwater mollusc Melanopsis praemorsa in the Kura River basin, Azerbaidjan. Secretory apparatus, excretory system, arming of tegument, and other structures of virgulate cercariae are characterized.

The checklist of Crustacea and water mites (Hydracarina) parasitizing fishes in the Volga River basin is presented. Hosts and areas of distribution are indicated for each parasite species. The checklist includes 20 species and 1 subspecies of parasitic Crustacea, and 8 species of water mites from 41 fish species. Five species of Crustacea, (Paraergasilus medius, Neoergasilus japonicus, Sinergasilus lieni, S. major and Lernea elegans morpha ctenopharyngodonis are considered as invaders.

Results of long-term investigations on the population dynamics of juvenile Atlantic salmon (Salmo salar L.) in the Keret' river (White Sea drainage basin) depending on the invading of Gyrodactylus salaris (Malmberg, 1957) and mass infestation of salmon with this parasite are presented. Gyrodactylus salaris was for the first time recorded in the Keret' river in 1992. During the period lesser than five years the parasite spread along the river. The rise in the infestation of salmon parr with G. salaris caused death of the fish host. As the abundance of juveniles decreased, adult salmon stocks dropped more than 25 times. It was shown, that after the decreasing in number of salmon juveniles following acute epizootic, infestation parameters dropped, and in some years G. salaris was not even found at all.

The comparative analysis of esterase changes in homogenates of the snails Lymnaea stagnalis and L. tumida bodies was carried out. Juvenile snails with shell size 2 mm, 3—4 mm, 5—6 mm and 7—8 mm were exposed to cercariae of the trematodes Echinoparyphium aconiatum and/or Moliniella anceps. The esterase activity was detected spectrofotometrically. The highest level of esterase activity in noninfected L. stagnalis was registered in snails with shell size 3—4 mm. The invasion of snails by trematode cercariae results in a change of esterase activity in the tissues of infected snails. The activity of easterases was increased in the infected L. stagnalis snails with shell size 5—8 mm at 2 days post invasion in comparison with control. The decrease of esterase activity in tissues of infected snails L. stagnalis (3—4 mm) and L. tumida (4 mm) was observed at 26 days post invasion by E. aconiatum only. The host size and parasite species was influenced on esterase activity in the snails.

Nematode community structure of the potato fields with different infection levels of potato cyst-forming nematode (PCN) such as 10, 30 and 214 cysts per 100 g of soil has been investigated. The influence of specialized parasite on nematode fauna and dominance character of different ecological-trophic groups were described. Parasitic nematode genera in natural meadow biocenosis and agrocenoses without PCN are Paratylenchus, Tylenchorhynchus, and Helicotylenchus. It is established, that Paratylenchus nanus was the prevalent species among plant parasites at low infection level. Larvae of Globodera prevailed in the soil with middle and high infection levels and substituted individuals of other genera of parasitic nematodes. The fact of increase in number of hyphal-feeding nematode Aphelenchus avenae was revealed.

On the base of morphometric analysis and investigation of sex ratio in some nematode species from murine rodents the next tendencies were revealed: 1. If the durations of life in nematode males and females are about the same, the sex ratio in a monoinfected host is near 1/3 males and 2/3 females. 2. Presence of other helminth species moves the sex ratio towards males, but in the case of polyinfection the percentage of males decreases again. 3. Solitary helminth specimens have minimal size, and as the parasite number in a host increases, the length and width of nematodes at first in crease, and then begin to decrease. Bounds of these increase and decrease depend on the size, as well as the taxonomic belonging of a nematode. 4. In the presence of other helminths, the decrease of size in a nematode species take place under lesser parasite number than in the case of nomoinfection. Decrease of the absolute size of nematodes and female percentage reduces energy demands of the parasite pool in a host body, because females are larger than males and moreover they spend nutrients and energy for reproduction. It leads to the reciprocal regulation of the helminth species abundance at the level of populations.

Fauna of parasitic nematodes from Chiroptera of the Samarskaya Luka has been studied. Seven nematode species has been recorded. Numbers of host specimens, indices of ex-tensiveness and intensiveness of the invasion, parasite abundance, and brief characteristics of the nematode species are given. Some nematode species were for the first time recorded in bats of Russia.

Metacestodes of Paradilepis scolecina (Rudolphi, 1918) Hsu, 1935 and juveniles of the nematode Contracaecum rudolphii Hartwich, 1964 have been found for the first time in the bream Abramis brama L. from the Curonian Lagoon of Baltic Sea. Descriptions and measurements for both parasite species are given. High infestation of bream with these parasites in an evidence of favourable conditions for the completion of their life cycles in the Curonian Lagoon.

Summary is absent.