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Vital observations and time-lapse filming of the spotted fever group of rickettsia in surviving cells from haemolymph of Alveonasus lahorensis showed some biological peculiarities in their development. The haemocytes from haemolymph of the newly infected ticks as well as haemolymph of the third generation of parenteral infected ticks four years ago were used for observations. The development of the rickettsia proceeds directly in the cytoplasm around cell organoids. The intensity of multiplication of rickettsia was depended on surrounding temperature of keeping and feeding of ticks. It was regularly observed the phenomenon of joining and following disjunction of rickettsia individuals. It is possible that a process, similar to the bacteria conjugation takes place in this case. Electron microscopy of the tracheal complex cells revealed two principal (vegetative and resting) forms of rickettsia with the characteristic ulfrastructural organization.

The attempt was made to associate the frequency of blocking the intestine of fleas with the number of plague microbes penetrated into it. The method was used of individual dose feeding of fleas with definite concentration of plague microbes. Not less than 60 000 plague microbes of the virulent strain must penetrate into the intestine of Xenpsoylla cheopis for the block to be formed. Mostly often the block develops at the infestation of a flea with average doses ranging from 60 000 to 100 000 microbes.

The formation of the plague block in Xenopsylla skrjabini Joff at temperatures from 13 to 28° and relative humidity 70—100% depends on the intensity of infestation of fleas with microbes of plague and feeding conditions. The duration and frequency of feeding and the specifity of host effect the block-formation at different degrees of the infestation. Whatever the number of microbes in fleas, the block-formation proceeds more quickly during a long contact of infested fleas with a host than during a short rate of feeding. The formation of the block depends also on the species of the host.

The ticks Hyalomma anatolicum of all the phases of the development (hungry and well-fed) were radiated by X-rays in the dozes of 1000 and 2000 rentgens. The action of 1000 r on the larvae and nymphs was revealed chiefly in the following phases of the life cycle. The analogous influence caused the doze of 2000 r on the hungry larvae. The same doze considerably oppressed the nymphs and hungry adults or proved to be lethal for the part of the nymphs as well as in a hungry state and in well-fed ones. The influence of X-rays in the doze of 2000 r on the nymphs and adults was displaced directly in a radiated phase. The larvae are more sensible in the well-fed state. The reproductive function of almost all the well-fed females, received from hungry adults radiated by 1000 r, is lower than that of the females received from the nymphs and from the larvae, radiated by the same doze.

A study was made of the survival of the tick Hyalomma anatolicum Koch, infected with Nuttallia tadzhikistanica. Observations were carried out at two temperature regimes (30±0.2° С and 15—18° C) on 536 ticks. Results of the observations statistically analysed indicate that the survival of H. anatolicum is almost unaffected by N. tadzhikistanica.

5 species of ixodid ticks were found to occur in the Leningrad region: Ixodes ricinus L., I. persulcatus P. Sch., I. apronophorus P. Sch., I. trianguliceps Bir. and Dermacentor pictus Herm. These species are unevenly distributed within the region and differ in their number. From ticks were isolated agents of tularemia and listeriosis (from I. ricinus and I. perculcatus), pseudotuberculosis and salmonellosis (from I. ricinus).

Tests were carried out intended to confirm the existence of factors inactivating microbes of plague in fleas Xenopsylla gerbilli minax Jord., Ceratophyllus laeviceps Wagn. and Leptopsylla segnis Schöncher. It was established that microbes of plague, introduced to fleas by means of apparatus for dose feeding, were inactivated very quickly (with different inactivation rates in different species). This is confirmed both by the reduction in the number of microbial bodies and the decrease in the number of infested individuals. Bactericidal factors were found to be present in adult fleas of any age and physiological state.

27 species of parasites were introduced into ponds of the European part of the USSR together with Ctenopharyngodon idella, Hypophthalmichthys molitrix and Aristichthys nobilis. Eimeria sinensis, E. cheni, Dactylogyrus lamellatus, D. ctenopharyngodonis, D. hypophthalmichthys, D. nobilis, D. aristichthys, Bothriocephalus gowkongensis are mostly often encountered. Sinergasilus major, S. lieni and L. ctenopharyngodonis were recorded from some ponds. D. lamellatus, S. major and L. ctenopharyngodonis caused diseases in Ctenopharyngodon, B. gowkongensis — in carps. Such local species as Ligula intestinalis and Digramma interrupta caused the death of Aristichthys nobilis.

In halcyons in the Democratic Republic of Vietnam and also in Primorje in the Maritime province of the Far-East region the authors discovered three species of trematodes of the genus Basantisia Pande, 1938; B. halcyonae sp. n.; В. longa sp. n. and B. ramai Pande, 1938. The genus Basantisia is transferred by the authors from the family Lecithodendriidae, where Pande placed it, in the family of Microphallidae. Pseudospelotremu macrovesiculata Chen., 1957 is a synonym of Basantisa ramai. It is supposed that the trematodes of the genus Basantisia have an area of affection in the limits of torrid zone.

A new species of the entomopathogenic nematodes, Neoaplectana agriotos sp. n., was found in the population of elaterids, Agriotes lineatus L., in Leningrad region. The nematodes of this species are pathogenic for imago, pupae and larvae of the elaterids. Mortality of the insect population came to 75 per cent. The description of N. agriotos sp. n. is given.

The author suggests to call a species of an animal, which can be a host of different categories for a definite species of helminth, a polyvalent host of a given species of helminth. The phenomenon itself is suggested to be called a polyvalent susceptibility to a given species of helminth. Due to analysis of various cases of polyvalent susceptibility to helminths the author has come to the following conclusion: polyvalent hosts are normally vertebrate animals whereas invertebrates can serve as hosts more seldom. Polyvalent hosts are encountered in trematodes, cestodes, nematodes and acanthocephals. Some polyvalent hosts can be only obligate, some others — both obligate and facultative ones of a definite species of helminth. Biological significance of polyvalent susceptibility involves a tendency to a secondary simplification of the life cycle of a given helminth due to a decrease in the number of hosts.

A new species of nematodes, Crassicauda costata sp. n., is described from specimens found in kidneys of the southern whale. The length of the body of the male is 320 mm, that of female — 940 mm, maximum width is 1.9 mm and 2.7 mm, respectively. The species described differs from all known other species of the genus by having numerous transverse elongated cuticular ribs in the anterior part of the body, which are an adaptation for reliable fixation in tissues of kidneys of the whale.

362 females and 372 males of Ditylenchus dipsaci from 26 species of artificially infested plants were morphometrically studied. It was found that most poorly developed were gonads of individuals from most resistant species of plants. It was observed a continuous row of variability of all characters of D. dipsaci from most injured plants (strawberry, polygonum) and practically resistant species (oat, mustard, maize). The amplitude of fluctuations of indices between extreme values was, however, significant. Due to such a variability size and proportions of the body cannot play a decisive role in distinguishing races of D. dipsaci.

There were established the circulation routes of Toxoplasma gondii of RH strain in the ticks Ornithodoros papillipes and O. moubata. In the intestine of the ticks, which were fed on white mice infected with toxoplasmosis, toxoplasms preserved from 3 to 7 days without penetrating the body cavity. When introduced parenterally, toxoplasms preserved in haemolymph of the ticks from 2 to 7 days During feeding on white mice infected ticks do not transmit toxoplasms and are absent in the coxal fluid.

Summary is absent.