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Many years of observations (1966—1981) in the southern part of Volga-Ural sands prove interspecific interactions between five species of fleas, specific parasites of Meriones meridianus, following the Gause's principle. The major mechanism for avoiding interspecific competition for the host is a temporal separation of the five species of fleas. During every season of the year, independent of the exchange of one species of fleas by others, their number on the infested host is maintained on the stable level which is regulated by overdispersion of fleas in the host population.

Observations on the changes in the fauna of forest land reclamation zones in the Novgorod region conducted within a period from 1968 to 1981 make it possible to forecast the reduction of hatching sites of mosquitoes of the genus Aedes and gadflies of the family Tabanidae by a factor of two and four, respectively, by means of open drainage. The hatching sites of Aedes can be liquidated by means of closed drainage and mosquitoes of this genus thus become unessential. On reclaimed land dear populated areas they will be replaced by C. pipiens and An. messeae populations. Open drainage of overmoistened small—leaved and mixed forests results in a three—fold and more increase of the number of Ixodidae ticks. A high level of the abundance of ticks will be maintained for decades while the biotope exists.

Common antigenic components were studied in 14 species and 7 genera of 3 families of gadflies. Common antigenic components of the family Hypodermatidae were studied most thouroughly. No antigenic affinity was found between the families of gadflies. As far as these characters are most distinct in quantitative respect in the family Hypodermatidae the author suggests a comparative youth of this family and recommends to use immunobiological reactions for classification and definition of phylogenetic affinity of gadflies and other endo and ectoparasites which have common antigenic structures. The possibility to use monopreparations for diagnosis and prophylaxis of diseases caused by gadflies larvae is considered.

The opinion of Maillard and Noisy, 1979 is confirmed that it is necessary to exclude the genus Atrispinum Maillard et Noisy, 1979 from the genus Atriaster Lebedev et Paruchin, 1969 and consider it a distinct genus. The genus Atriaster has the following characters: genital atrium is armed with a crown of lateral hooks, pair of long anterior hooks and a bundle of median ones, vagina is double; members of the genus Atrispinum have no pair of long anterior hooks and vagina is single. A. bifidacanthus Mamaev et Paruchin, 1973 has a double vagina and undoubtedly belongs to the genus Atriaster. A new genus, Sparicotyle g. n., is suggested for the species Microcotyle chrysophrii Van Beneden et Hesse, 1863 and a new name, Pagellicotyle nom. nov., for the genus Bychowskicotyla Unnithan, 1971 (monotypical genus for Microcotyle mormyri Lorenz, 1878) as far as the previous name is preoccupied.

A new species of cestodes, Echinocotyle (Echinocotyloides) rostratum sp. n., is described from Philomachus pugnax of northern Prichernomorje. The species is characterized by a short (up to 6 mm) narrow (up to 0.28 mm) strobile with over 100 joints, small scolex, its diameter reaching 0.12 mm, with very long proboscis and by proboscis hooks reaching 0.020—0.025 mm an length. Long (0.150—0.195 mm) bursa of cirrus reaches the aporal edge, cirrus conical, unarmed, 0.040 mm in length, evaginated Furmann's body 0.060 mm in length. Differential diagnosis of close species, E. ukrainensis, E. kornjushiniy, E. dubininae, E. multiglandularis and E. druzniensis of the subgenus Echinocotiloides is given.

Catecholamines (CA) were found in the nervous system of cercaria and immature N. attenuatus by means of the hystochemical method with glyoxylic acid. Three pairs of relatively large neurons with СA were recognised. The first pair is located at the beginning of dorsal nerve trunks. The second and third pairs of cells are near the abdominal trunks approximately at the level of the middle and the beginning of the hind fourth of the body. Nerve fibers containing СA were found in the cerebral commissure, longitudinal nerve trunks and in numerous commissures especially on the abdominal side of the body. In immature N. attenuatus there were found short straight commissures between the ventral and the dorsal trunks along with annular and semi-annular ones. Fibers envelope the oral sucker and those parts of the body where are located ventral papillae. In cercaria fibers with CA innervate the tail too.

1181 yearlings of pelyad (Coregonus peled) and its hybrids with Siberian (Coregonus lavaretus pidschian) powan were dissected. A calculation of loss in mass per 100 kg of catch at different levels of fish infection with metacercariae of diplostoms was made. Losses increased in direct proportion to the average number of metacercariae per 1 g of mass of fishes. With 1.5 metacercariae per 1 g of mass of fish population losses amounted to 1/2 of potentially possible production.

Studies were conducted of the content of ferments with which metacercariae of trematodes of the genus Diplostomum affect the tissues of the host's crystalline lens. The following ferments were found in exudates of metacercariae: pepsin, cathepsin, hyaluronidase and lipase. Their activity depends to a great extent on temperature. Considerable changes in the biochemical content of crystalline lens infected with the parasites were found. The character and force of pathogenic effect of diplostomatids on fishes depend on the factors associated with activation and inhibition of ferments of metacercariae, temperature and the presence of ions-inhibitors in particular.

Data on morphology and biology of Cercaria telorchis sp. IV found in Lymnaea auricularia from waters of Azerbaijan and these on morphology of metacercarians reared experimentally in Rana ridibunda and its tadpoles are given.

17 males and 7 females of Sergentomyia (Parrotomyia) gobica sp. n. were collected in Tsubulur-Khara-Nuru mountains (Bayan—Khongor region) of the Mongolian People's Republic in August of 1980 and in July of 1982. The new species is similar to S. (Parr.) sumbarica (Perfiliew), 1933.

A new species of black flies, Wilhelmia talassica Yankovsky, sp. n., is described from north western Kirgisia.

A description of a new species of parasitic isopodes of the genus Anilocra Leach, 1818 found in fishes from coastal waters of Peru is given.

A new species, R. asiaticus sp. nov., from rodents of north-eastern Asia is described. The developmental cycle of the species is studied. Three stages of larvae are described and periods of their moulting established.

A brief description of the species Vairimorpha hybomitrae which earlier was described as Nosema hybomitrae is given. It has two types of sporogony: one — with single thick-walled spores 4.8+0.13 x 3.63+0.02 in size, the other — with thin-walled mononuclear oval octospores 2.0—2.4 x 1.5—1.8 enveloped by a pansporoblastic membrane. The species was found in larvae of gadflies of the genus Hybomitra collected in Karelia.

Summary is absent.

Summary is absent.