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Larvae of Ixodes persulcatus and Hyalomma asiaticum were feeding permanently on hosts attacking them daily by groups ot 5—20 ticks, and also fed by groups of 30—40 and 100 ticks with the interval 20 days. The factor of the host species in the case of 1-st feeding of ticks did not influence significantly on the weight of engorged ticks and also on the percent of larvae, which had finished the feeding and moulted to nymphs. In the cases of 2-nd and 3-rd feedings the significant part of ticks died before the end of feeding, and engorged ticks had less weight and lower capability to moult. The rate of anti-tick resistance of hosts depends upon the species of the host and upon the number of ticks fed up. In the case of permanent feeding of larvae during 40 days the anti-tick resistance was low or completely absent.

Repeated feedings of larval Amblyomma hebraeum ticks on laboratory mice results in strong decrease of engorged tick yield (from 65—73% after primary feeding to 11% after secondary feeding). Laboratory mice differ essentially in this respect from rabbits and sheep which are unable to acquire the resistance (see Norval, 1978) to larvae of this tick.

In the fleas Leptopsylla segnis settled on white mice the steady egg-laying took place under conditions including three factors—darkness, high relative air humidity (80—100%) and the "smell of host nest". The absence of anyone of these factors reduced an egg-production by 34—56%. The removal of the "smell" source coupled with substitution of high air humidity on low one (50—60%) interrupted the egg-laying almost completely inspite darkness or light. Owing such reaction on joint influence of the "smell of host nest" and air humidity the fleas are capable to interrupt and to recomence egg-laying depending on either the host is outside or in the nest.

It is demonstrated that in the regions, where Ixodes persulcatus and I. ricinus are sympatric, the incidence and prevalence of Borrelia burgdorferi among the latter tick species is higher. In areas, where the Ixodes persulcatis population infected with Borrelia were met, the percent of infected I. ricinus was 3—4 times more and the number of detection of borrelia infected specimens was 9 times higher than in the regions, where I. persulcatus was absent. The hypothesis is proposed, that the tick I. persulcatus is a carrier and source of the most virulent and acarotropic borrelia form. It is stated, that the reaction of the borrelia infected Ixodes ticks (I. persulcatus and I. ricinus) on the plant odour is changed. It is supposed that such changed plant odour depentant behavior would be able to be enhancer of the I. persulcatus — I. ricinus borrelia exchange process.

Mechanoreceptive sensilla in chiggers include nonspecialized setae (tactile mechanosensetive sensilla) of several morphophysiological types, and trichobotriae (vibrareceptor organs). Trichobotria (or pseudostigmal organ) contains two types of mechanoreceptive neurons. The first type forms a tubular bodies in dilatation near the apex of sensory cilium, the second one forms an electron-dence bodies in the same region. So, trichobotria of chiggers combine features of chordotonal sensilla of insects and of usual trichobotria of insects and arachnids.

The structure of hard body parts of Dactylogyrus markewitschi Gussev, 1955 was reexamined basing on new collected materials. Among collection materials labelled as D. markewitschi we have discovered the new species D. lebedevi sp. n., which is described, and D. guangxiensis Long et Tao, 1982, which is redecscribed herein. The figures of Dactylogyrus species with the procryptomeres type of copulatory organ are given. Dactylogyrus species from gudgeons are arranged into 8 morphological groups as follows: 1. D. guizhouensis Long et Tao, 1982, 2. D. finitimus Gussev, 1955, 3. D. cryptomeres Bychovsky, 1934, 4. D. navicular is Gussev, 1955, 5. D. singular is Gussev, 1955, 6. D. maximus Gussev, 1955, 7. D. gnathopogonus Yamaguti, 1963, 8. D. sparsus Gussev, 1955. The predisposition of these morphological groups to 8 genera of gudgeons is analysed. The genera of gudgeons basing on morphological groups of Dactilogyrus species associated them are arranged into two groups as follows: the group Saurogobio, Pseudogobio, Gobio and the group Chilogobio, Sacrochilichthys, Paraleucogobio; the genera Rostrogobio and Gnatopogon have rather separate position.

Different conceptions on system of the trematode suborder Didymozoata are briefly considered. New system of Didymozoata is proposed. 2 families, 6 subfamilies, 12 tribes and 70 genera are recognised. Diagnoses and key are proposed to families, subfamilies and tribes, all genera included into latter ones are listed.

Experiments were carried out on carps of the age 0+ captured in the Kiev region (fish farm "Nivka"). Morpho-physiological characters in fishes infected with the cestode Bothriocephalus acheilognathi differ from ones of noninfected fishes both in conditions of starvation and of feeding by standard granular combine food. The reliable decrease of absolute mass of the body and some internal organs in fishes was stated in case of starvation during 20 and 30 dayes. The reliable decrease of absolute and relative content of protein in a liver and a kidney of infected fishes, which starvated 10 and 20 dayes, was observed. During all time of experiments (30 dayes of feeding and starvation) the relative content of protein in immature B. acheilognathi taken out of carps, which starvated during 30 dayes, was higher than in adult cestodes. The high rate of relative content of protein was observed in adult cestodes taken from carps, which starvated during 30 days, and the high rate of absolute content of protein was observed in all ages of cestodes, which fed together with fishes during 30 days. A starvation and a feeding of carps infected with bothriocephalus do not change the dynamics of protein rate in cestode tissue in dependance of their number in intestines. The relative content of protein in anterior region of the bothriocephalus body is higher than in posterior region of it. In case of 20 days starvation of fishes infected with cestodes the rate of protein in different regions of the bothriocephalus body increased 2.8 times in comparision with cestodes taken from fishes, which starvated 10 days.

Description, figures and differential diagnosis of Leucocytozoon bennetti, detected in roller Coracias garrulus (Coraciidae), are given. Gametocytes of the new species are spherical or elliptical in shape. A host-cell nucleus present in growing gametocytes only and it has a cap-like or band-like shape. The mature gametocytes eliminate the host-cell nucleus and appear as naked parasites. The gametocytes of L. bennetti are similar to L. caulleryi from chickens. Both parasites are the only known species of Leucocytozoon which have mature gametocytes in host-cells lacking a nucleus. L. bennetti is distinguished from L. caulleryi by its smaller size of full grown gametocytes and by the shape of the host-cell nucleus of the stage, which precedes the enucleation.

Conditions favouring the sharp increase of risk to be infected with cercariosis (caused by trematode cercariae Trichobilharzia ocellata Brumpt, 1931, Schistosomatidae) were examined in Moscow region (Russian Federation). Main factors of worsrening the cercariosis situation are as follows, a) The increase of environment pollution by everyday wastages and the overgrowing with macrophytes in internal water basins of Moscow, that makes favourable conditions for the development of molluscs, which are intermedial hosts (mainly Lymnea ovata and L. auricularia). b) The sharp increase of number of ducks (mainly mallard Anas platyrhyncos), which are final hosts, that is a result of bird escaping from farms (approximately in 60—70-th) and of high adaptation of these birds to city water basins. The detailed estimation of the cercariosis situation in 89 water basins of different types in Moscow and recreation zone was carried out. Examples of charting the zones with different risk degree of cercariosis infection are given. It is stated that at current time the cercariosis becomes a significant and widely distributed medical problem, which is most important in cities (including such large one as Moscow). Prophylaxis recommendations are proposed.

Twelve species of mites of the genus Schizocarpus (Chirodiscidae) have been collected from 14 specimens of the Canadian beavers Castor canadensis Kuhl, 1820 at the experimental beaver farm in the Voronezh reserve. One new species Scizocarpus anomalus sp. n. is described; 7 species previously known only from the European beaver Castor fiber L., 1758 are recorded from Canadian beavers examined. Sustaining of beavers of both species in the same fur farm and impoverishment of ectoparasite fauna on the Canadian beaver under conditions unusual for it apparently favoured a transfer of mites from the European to Canadian beaver. A list of lectotypes from the type series of species of the genus Schizocarpus earlier described by H. Dubinina (1964) is given.

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