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Seasonal patterns of oviposition in a synanthropic unautogenous population of Culex pipiens pipiens mosquitoes from 69 suburban settlements (60° 30' N, 30° E') of the Leningrad province were studied during the period 1998—2002 years. The numbers of egg rafts laid in six artificial pools (barrels) were counted every day; altogether 692 rafts were collected. The general patterns of oviposition activity were similar for ail studied years, in spite of their differences in the summer temperature regimes. The first peak of oviposition was observed during the second decade of July, the second peak — during the third decade of July—the first decade of August. The first and second summer generations of mosquitoes were responsible for these oviposition peaks, whereas the third generation completely entered the reproductive diapause. Thus, the oviposition activity was successfully used for populational monitoring of C. p. pipiens, that was for the firstime recommended by Madder and co-authors (1980), taking into consideration the simplicity and economy of this technique. The differences in the attractiveness of distinct reservoirs for oviposition were recorded. The females preferred the barrels located on open sun-lit space and waters with organic pollution settled by mosquito larvae. Windy and rainy weather and also low (below 10°C) night temperatures suppressed mosquito oviposition.

Structure of consortia as an animal community inhabiting a mammalian burrow with an example of the little souslik Spermophilus pygmaeus Pallas from Western Kazakhstan was studied. Species composition, numbers and distribution of invertebrates in different types of burrows and nests of the little souslik were examined on the background to their food dependencies on the host. The consortia is considered as a system of concenters around the host of burrow (center of community, CC). Recognized concenters are given with ranks based on food relations between invertebrate inhabitants and CC: concenter of I rank includes direct parasites and predators of CC, II rank is represented by consumers of dead bodies of the souslik and its life activity products; III rank includes predators and parasites of souslik's cohabitants, and concenter of IV rank encompasses animals, which use the burrow as a refuge only. Within limits of each concenter, a number of "rondos", groups of animals attributed to certain systematic category, for example ticks, gamasid mites, certain insect orders etc., may be recognized.

Flight trajectories of horse flies Hybomitra attacking a single host (a cow) have been registered on record cards by the method of Knipest (1981). The trajectories in a search on integuments of preferred places for feeding are described, as well as the responses caused by defensive activity of the cow are considered. The role of sensory systems in a regulation of the feeding reactions of the horse-flies is discussed.

The morphology and fine structure of the female reproductive system of allassogonoporid trematode Allassogonoporus amphoraeformis have been described for the first time. The ovary consists of the germ cells being at various developmental stages and supporting cells of two types. The oviduct, seminal receptacle with its short duct and the proximal portion of Laurer's canal are lined by flattened cellular epithelium with lamellae and cilia on its luminal surface and well-developed basal infoldings. The distal part of Laurer's canal and metraterm are tegumental in structure and are characterized by sparse secretory inclusions and lacking of spines. Mehlis' glands of two types open into ootype. The uterus wall is composed of highly flattened epithelial cells surrounded by basal lamina and sparse muscle bundles. Vitelline lobules consist only of the vitelline cells at various developmental stages. The mature vitelline cells contain two types of inclusions: vitelline droplets and rarely scattered lipids. Vitelline ducts are lined by cellular epithelium with highly folded luminal surface and devoid of cilia. Presented results are compared with earlier obtained data on other lecithodendrioiden trematode Prosthodendrium ascidia (Podvyaznaya, 1990).

Fine morphology of external tegument (surface complex) of young and mature acanthocephalans Filicollis anatis and young Neoechinorhynchus crassus is described. Based on comparative analysis of the obtained results and literature data, the surface complex of all examined acanthocephalans is shown to have principally similar structure at all stages of life cycle. Differences between species examined are found in quantitative characters only and they are related either to age or ecology of worms (embryonic larvae).

A comparison of simple probability analytic model of infection rate depending on host's age with natural infection rate of mussels (Bivalvia: Mythilidae) with metacercariae Himasthla elongata (Trematoda: Echinostomidae) was carried out. Data on the natural rate of infection were accumulated during 3 years; 1152 individuals M. edulis were collected in two horizons within fucoid zone of the Kruglaya inlet and the Chupa inlet of the Kandalaksha bay (White Sea). A size of shell and number of H. elongata metacercariae were defined for each mussel using compressive dissection technique. The infection of mussels per year within our model is considers as independent evens: Pn =1-(1-p)n, where n is the age of mussels, Pn is the theoretical part of infected n-year mussels, p is the probability of infection within one year. The probability of infection within year is assumed equal for every age of host. The estimate of probability of infection per year on the basis of sample of n-year's mussels was calculated as pn = 1 - , where n is the age of mussels, In is the part of infected n-year mussels. The retransformed weighted average value of arcsine-transformed pn was used as p in our model (p=0.3476). Statistically significant differences between empirical and theoretical (calculated from our models on the basis this value) infection rates were not found (P>>0.05 x2-test). Moreover, statistical significant differences were absent (P>0.05 Fisher exact test) in pairwise comparisons between empirical and theoretical infection rates for each age of mussels. The model does not take into consideration an effect of such factors as host's resistance, host's migration and increase of mortality in infected hosts. The absence of significant differences between the empirical and theoretical infection rates allows to suggest, that mentioned factors under the conditions of the Kruglaya inlet do not influence essentially onto infection of mussels with metacercariae H. elongata. This conclusions is in certain inconsistency with essential differences in such characteristic as an individual resistance of mussels to the infection with metacercariae H. elongata, detected in experiments in vitro (Gorbushin, Levakin, unpublished data). Analysis of intensity of the invasion of metacercariae H. elongata into mussels allows to suggest the existence of differential death rate of the hosts, which is exhibited in individuals over 7 years old. Studied example of mussels infected with metacercariae H. elongata under conditions of the Kruglaya inlet shows that the simple probabilistic model of the natural infection rate is usable for this kind of investigation. Our study also allows to conclude that in this case the infection rate of hosts is mainly determined by stochastic reasons. However, in some cases the probability of infection rate may not depend on the age and size of the host. The study of infection rate can not be used for analyses of individual differences of hosts in a resistance to parasites and an infection ability of the parasite.

Cysticercoids of the cestode Unciunia raymondi Gigon et Beuret, 1991 (Cyclophyllidea: Dilepididae), a parasites of palaearctic thrushes (Turdus), taken from spontaneously infected Geotrupes and black wireworm Cylindrojulus in the North-eastern Altai, is described. An identity of cysticercoids of U. raymondi and Ditestolepis diaphana sensu Kisilewska, 1960 has been stated. During the development within the fibrillate membrane, the metacestode of U. raymondi separates the cercomer from the cyst anlage in the late scolexogenesis. There is no the primary lacuna in the lamellated cercomer without any musculature. Its primarily smooth surface gradually becomes sulcate and plicate. In the result of some segments break-up, the cercomer lamella comes to be perforated with its margins deeply jagged. Metacestode of U. raymondi metacestode is compared with cryptocercus of Dilepididae, which also develops within the fibrillate membrane. Based on peculiarities of the morphogenesis of cercomer, the cysticercoid U. raymondi is assigened to a new morpho-ecological type, the placocercus.

Analysis of original and literary data permits to conclude that the life cycle in Orthonectida may be characterized as a monohost — monoxenous one, including regular interchange of three generations: asexual and parthenogenetic ones, which are represented by parasitic plasmodiums, and sexual generation, represented by free living and non-feeding males and females or, rarely, hermaphrodites. The sexual individuals are bilaterial, while the parasitic ones are anaxonic. The life cycle of Orthonectida includes the agamic reproduction, apomictic parthenogenesis and sexual reproduction regularly following one another. The life cycle of Orthonectida can be considered as a combination of metagenesis and heterogony. So far, such combination has not been described in any group of metazoan parasites.

Since investigations of Fisher and Sanborn (1964), the most popular point of view on pathological alterations in the development of insects is the statement that microsporidians can produce and secrete the insect juvenile hormone in infected tissues. We suppose that the juvenilizing effect of microsporidian infection may be a consequence of stress induced by the protozoan invasion. To our opinion, microsporidians can not be a source of juvenile hormone in parasitized insects because of several reasons. 1. The juvenilizing effect of infection may be explained by other reason, that is the stress effect of invasion. 2. Untill now nobody can find juvenile hormone in microsporidians. 3. An increase of juvenile hormone titre either alters non-metabolic activity of fat body or alters it in a way that is not favorable for microsporidia. 4. Some effects of the microsporidian infection more resemble an action of ecdysone, but not juvenile hormone. Hypothesis of parasitic stress can explain this, while hypothesis of production JH by microsporidians can not. 5. An effect of invasion by parasites of other systematic groups onto the hormone balance is of the same type. But nobody thinks that other parasites can produce juvenile hormone. Nevertheless it is clear that a high titre of the juvenile hormone is favorable for the microsporidian infection in larvae, especially the last instars. The most descriptions of microsporidian infections are related with this age of insects. Juvenilizing effect of Nosema implantant in the work of Fisher and Sanborn (1964) may be easily explained by decreasing of JH-esterase activity. But in this case the decrease of JH-esterase activity after the implantation of infected tissue in a healthy insect should be explained. We suppose that this fact witness the existence of stress-factor produced by damaged cells of fat body that can enter the healthy cells of fat body and inhibit the activity of JH-esterases.

Tetraonchus strelkowi sp. n. described from gills of the lenok Brachymastix lenok from the Tola river (Mongolia) differs from T. roytmani by morphometric characteristics of the haptor and copulatory complex.