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V.N. Beklemishev (1890—1962), an outstanding Russian parasitologist, was a founder of biocoenological parasitology and many of his ideas exceeded the level of development of science of that time. He formulated the notion of "parasitic system", which was regarded by him as a population of the parasite with all populations of its host, forming a part of biocoenosis. The term "ecological group of species" involved the set of all morphophysiological adaptations, which ensure for the species the possibility of existence in its environment. In their essence they coincide in many respects with modern terms, microecosystem and ecological niche. The concept of parasitic systems can serve as a logical basis for mathematical modelling of parasite populations.

The capacity of An. sacharovi and An. pulcherrimus to be infected with P. gallinaceum and to transmit the agent to the vertebrate host, a chick, has been established. Sufficient differences have been found in the extensiveness and intensity of infection of different species of mosquitoes and in other characteristics reflecting the agent-vector relationships.

22 500 mites were collected from 4515 rodents over a period of 5 years in the Sikhote-Alyn reserve. The abundance dynamics of 4, out of 5, most numerous species of mites (Laelaps pavlovskyi, L. clethrionomydis, Eulaelaps stabularis, Haemogamasus serdjukovae) depends on the cyclic fluctuations in the number of rodents. A direct connection between the annual and, to some extent, seasonal dynamics of the abundance of parasites and that of their hosts is most distinct in L. pavlovskyi, an epizoon parasite of the large Japanese field mouse. At the same time the abundance of Hg. ambulans, a multihost parasite of small mammals, does not depend on the number of animals. Certain regularities in the abundance dynamics of gamasid mites in connection with that of their hosts, rodents, is discussed on the basis of obtained material and literary data.

Descriptions, figures and differential diagnosis of Haemoproteus pallidus sp. n. and H. bacillaris sp. n., detected in Muscicapidae, are given.

The classification of the additional ventral bar of dactylogyruses of the world fauna according to its type was carried out. Its main functions are the strengthening of the ventral side of the haptor, support and muscular connection between the 1st and 2nd pairs of the marginals. The ventral bar has never been connected with the anchors. Dactylogyruses with one bar are more primitive by this character than those with two bars. However, in some cases a reduction of this structure takes place. In the Palaearctic and Amur-Chinese faunas the formation of individual types of the additional bar carried out independently and in parallels. In different faunas in different groups of dactylogyruses a repeated origin of the ventral bar is quite evident. Between North-American and Palaearctic as well as between Palaearctic and Indian faunas an exchange of double-bar dactylogyruses occurred On the other hand, varicorhini-group and one-bar dactylogyruses from Percomorphi are initially spread in different faunas. The separation of dactylogyruses into two genera according to the presence or absence of the additional bar is not justified. The ventral bar type together with the other features of Monogenea can be used as a character supplementing the "type of copulative organ" character for the revision of the genus.

Morphological indices of the cestode Proteocephalus pollanicola from Coregonus pollan of Lough-Neagh (Northern Ireland) have been studied. According to the degree of variability the characters are arranged into 3 groups: 1. With a low degree of variability (CV is about 10%): cirrus bursa length, scolex length and ratio of cirrus bursa length to proglottis width; 2. With an average degree of variability (25>CV>10%): sizes of lateral and apical suckers, testes, scolex width, cirrus bursa width, proglottis width and number of testes; 3. With a high degree of variability (CV>25%): proglottis length. A comparison of morphological indices of P. pollanicola to those of P. exiguus from the close to C. pollan species C. lavaretus, C. autumnalis and C. albula was carried out. A similarity of P. pollanicola to the ecoform P. exiguus from C. lavaretus was noted. The obtained data support the results of investigations of Kaukorante, Mednikov (1988) on genetic affinity of Coregonus pollan and C. lavaretus and their opinion that C. pollan is a form of the latter.

Study of the vast material has shown that there is a dependence between the infection rate of fishes with dactylogyrids, the number of groups formed by these parasites on the gills of their hosts and the number of worms in these groups. This dependence is satisfactorily described by the equations of a straight line. It has been established that in the worms from roach the groups can consist of parasites belonging to different species. In different periods of summer period dactylogyrids (from roach, pope, rudd) form different numbers of groups as well as varies the number of worms participating in their formation. This seems to be connected with the changes in the age composition of the populations of Dactylogyrus species.

The functioning of different proteinases hydrolysing proteins in a wide pH range, most of which display activity in the alkaline zone of pH, on the digestive-absorptive surfaces of the parasite and host has been investigated. The dynamics of desorption of these proteinases from the intestine of fishes and tegument of cestodes has been studied. It has been shown that the worms possess less proteolytic activity and less capacity for adsorption of proteinases as compared to the intestines of their hosts. The dependence of proteolytic activity of desorbed fractions on the incubative medium temperature has been noted: with the increase in temperature the enzymes, bound closely with the membranes, increase their capacity to hydrolyse proteins. The predominance in cestodes, as compared to the intestine, of easily desorbed fractions D1 and D2 (in the percent ratio of the total proteolytic activity of all fractions) has been detected.

A relative DNA-content of the nuclei of 16 isolates of the lower trypanosomatids was studied by the flow cytometry method. The trypanosomatids were attributed to 6 species of 3 genera : Blastocrithidia, Leptomonas and Proteomonas. The parasites have been isolated from 5 species of insects belonging to 3 families of Hemiptera. The DNA-content in the cells of all examined isolates, including the cells of the clones of the same species, altered no more than 10%. The cell populations with different ploidy were not found. Molecular caryotypes consist of 9 to 12 chromosomes, each chromosome being from 240 to 1000 kilobases in size. The caryotype of L. occidentalis and L. habiculae differs from all isolateds investigated earlier.

The microsporidium of the genus Parathelohania from larvae of Anopheles messeae has been studied with the electron microscope. The spore ultrastructure of this microsporidium is similar to that of P. illinoisensis. The numbers of thick and thin coils of the polar tubes of this microsporidian species are equal but the sizes of the spore posterior constrictions are different. This microsporidium is considered to be a form of P. illinoisensis — P. illinoisensis var. messeae.

Observations on the Triaenophorus crassus invasion in Coregonus lavaretus and Esox lucius were carried out in the period of 1984 to 1989 in the Verkhnetulomsk water reservoir and Pechozero waterbody (the Pecha river) which form a common basin. Significant differences were noted in the infection rate of fishes with this parasite in the above waterbodies. In Pechozero, where there are preserved natural conditions and therefore an ecological equlibrium in the host-parasite system, T. crassus is not abundant and the infection rate of C. lavaretus and E. lucius with this parasite is low. In the Verkhnetulomsk water reservoir, due to the dropping out of the amphipod group of benthos from the biocoenosis of the waterbody, there has been formed a close ecological connection between copepods, C. lavaretus and E. lucius that resulted in the increase of T. crassus and gave rise to Triaenophorus infection of C. lavaretus here.

Female and protonymph of Steatonyssus aglaiae sp. n. found on Rhinolophus ferrumequinum Schreber, 1775 in the Crimea are described.

Two species of fleas, Spilopsyllus cuniculi Dale, 1878, and Stenoponia tripectinata tripectinata Tiraboschi, 1902, were reported in European rabbit and small rodents (common field mouse, yellow-necked field mouse, house mouse) respectively, of the Crimean peninsula. The finding of new for the fauna of the Crimea species of fleas demonstrates new changes in its fauna and enlarges the picture of the distribution area of these species, thus supplementing the available information on the ways of the fauna formation of the peninsular as a whole.

It has been shown that the resistance of muscular larvae of Trichinella spiralis to the effect of low temperatures depends on the conditions of freezing and composition of media possessing cryoprotective properties. It has been established that under optimal conditions (medium of microenvironment, conditions of freezing) during the storage in liquid nitrogen muscular larvae of T. spiralis preserve 50 to 60% of their resistance by the character of mobility and 11 to 15% by their capacity for reproduction. The question of creation of low-temperature bank for trichinells in discussed.

A composition of secretory proteins of plerocercoids of the cestode Digramma interrupta and their enzyme activity have been studied. It has been shown that pierocercoids produce 26 secretory proteins with molecular weight range of 3.9 to 112.2 kDa. These secretory polypeptides possess protease, DNAase and RNAase activities.