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A brief account is given of a role of the host immunological status in control of giardiasis, the character of humoral immune response and the development of the acquired resistance.

Sphaeromyxa schulmani sp. n., Myxidium baueri sp. n., M. asymmetrica sp. n., Myxoproteus moseri sp. n. have been recorded from south-western Atlantic fishes. Myxidium bajacalifornium Noble, 1966 is recorded in the south-western Atlantic for the first time. Myxidium coryphaenoidium Noble, 1966 is found in new hosts — Coryphaenoides holotrachys and Salilota australis. The description of Myxoproteus meridionalis Evdokimova, 1977 specified.

Penaeid shrimps are presently being reared commercially in the United States and elsewhere. Parasites and diseases, however, continue to remain a problem in most rearing facilities. Viruses, algae, bacteria, fungi, ciliates, microsporidians, digeneans, cestodes, nematodes, and miscellaneous conditions include representatives that have an effect on aquaculture, influence hosts in their natural environment, and produce potential public health problems.

Seasonal dynamics of Perca fluviatilis L. infection with the cestode Proteocephalus percae Müll. was investigated in two lakes of Karelia. 2480 fishes were examined. It has been established that the annual cycle of the parasite distribution in the population of its definitive host can be modelled by means of trigonometric polynom of the fourth power.

Mechanisms of adaptation to various salinities in cestodes Triaenophorus nodulosus and Eubothrium rugosum, parasites of freshwater fishes, were studied. It was shown that the outer cytoplasm of tegument of these cestodes is unpermeable for water. Its entrance occurs through isolated canals in the tegument first discovered during ultrastructural investigation. Volume regulation of T. nodulosus is accomplished due to changing of volumes of subtegumental cells, while that of E. rugosum due to changing of the intercellular space. The subtegumental cells of E. rugosum are permeable for water and salts to a lesser extent than those of T. nodulosus.

Dopamine and 5-hydroxytryptamine have been spectrofluorometrically identified in tissue homogenates of trematodes parasitizing the lung of the frog Rana temporaria. The concentration of dopamine has been found to range from 0.8 to 2.5 µg/g of wet weight. The head region (including the oral and ventral suckers) contains 0.420 +0.036 µg/g (0.35 +0.04 ng per 1 helminth) of dopamine, its amount is equal to 1.270 +0.127 µg/g (7.2 +1.0 ng per 1 helminth) in the rest of the body. Dopamine is likely to be related not only to the functions of the nervous system but may possibly play a certain part in the egg shell formation of a trematode. The 5-hydroxytryptamine concentration in the helminth head region (4.5—5.9 µg/g) is considerably greater than that in the rest of the body (0.083—1.146 µg/g). Noradrenaline was not detected.

1903 specimens of sandflies and mosquitoes were examined for their spontaneous infection with larvae of Thamugadia ivaschkini. The experimental infection of sandflies and mosquitoes was conducted on infected lizards. It has been established that the vectors of this filaria in the south of Turkmenia are sandflies of the genus Phlebotomus and Sergentomyia arpaclensis. The development of the helminth carries out in thoracic muscles of sandflies, the first infective larvae appear in 7 to 17 days after the infection of vectors.

In 10 altitude-belt complexes of Dzhoysky ridge (West Sajans) during the summer period of 14—17 years the abundance of small mammals and imago of the taiga tick and the abundance of engorged larvae and nymphs of I. persulcatus was studied. The obtained results have shown that fluctuations in abundance of mammals and imago of ticks are not, as a rule, beyond the limits of a range of critical levels of abundance, which is defined as e^e=15.15. Fluctuations in the abundance of nymphs can cover two ranges and those of larvae up to three ranges. The amplitude of fluctuations in abundance of all groups of animals in question is minimum in optimal altitude-belt complexes and rises with an increasing effect of limiting factors. The decrease in the amplitude of fluctuations of nymphs as compared to larvae and that of imago as compared to nymphs can be, apparently, explained by a stabilizing effect of larval diapause on the abundance of nymphs and larval and nymphal diapause on the abundance of imago. Critical levels of abundance are assumed to be used as criteria of co-members stability in a parasitic system of the tick-borne encephalitis nidus and for classification of nidi with a regard for this character.

Feather mites are associated with all orders of birds except Penguins. Up to now 1626 species of feather mites assigned to 24 families have been described in world fauna. We have arranged all these species in a table representing a number of species and genera of feather mites of each family recorded from birds orders. The feather mites are constant obligatory parasites and usually are transmitted through direct contacts between birds of the same species. The co-evolution of feather mites and birds is demonstrated by the majority of host-parasite associations. At the same time there are many examples of discordance between the classifications of birds and mites. The co-evolution is disturbed by the accidental exchanges of parasites between different unrelated groups of hosts. The recent distribution of feather mites on birds appears to be a result of continuous co-evolution and many mites' exchanges which took place in past epochs.

In 1979/80 studies were undertaken of the fauna and phenology of Tabanidae from the Leningrad and Pskov Districts. By their abundance and number of species taiga and taiga-forest species make the principle part of the fauna in the subzone of southern taiga of the Leningrad District. The mixed forests of the Pskov District are characterized by the prevalence of taiga-forest species. H. bimaculata, H. pluvialis, H. arpadi, H. lapponica and H. lundbecki are dominant in the Leningrad district while H. bimbaculata, H. italica, and H. lundbecki are most abundant in mixed forests of the Pskov district. The activity period of tabanids in both regions lasts about 50 days. Mass flight lasts from 15 to 22 days.

The mouth parts and the whole head capsule of H. acanthopus are highly specialized and adapted to getting food in a stickily definite way. The mouth parts are represented by proboscis and piercing complex which consists of dorsal and ventral stylets. During feeding the proboscis penetrates the epidermis and piercing complex reaches the corium papillary layer and penetrates the blood vessel's lumen. Because of a small length of its stylets the louse can suck blood only from the most superficial subepidermal capillary plexus. A small external cliameter of the piercing complex enables it to penetrate the vessel's lumen with minimum damages. The ventral stylet provided with dentate structures performs the piercing of integument while the absorption of blood carries out along the duct inside the dorsal stylet. The internal diameter of the food duct does not exceed 1.7 µ. The gut contents of an engorged louse is homogenous, without intact blood cells. Apparently, formed elements become destroyed under the effect of insect's saliva just in the vessel's lumen and a louse sucks haemolysate.

Summary is absent.

Summary is absent.