Abstract. A comparison of the behavioural peculiarities of Ixodes persulcatus Schulze, 1930 (north-western population, Russia) and Ixodes ricinus (L., 1758) from western Russia and Denmark was determined by using two methods. Method 1 involved a sojourn of ticks on vertical plastic sticks and showed that the questing behaviour of I. ricinus nymphs was dependent on temperature and relative humidity (RH). A significantly greater number of nymphs quested at 22°C and 100% RH than at 18°C. When the humidity was reduced to 30% all of the nymphs departed. In the second method, the activity of ticks on an inclined "ticksdrome" was estimated. The activity of I. ricinus adults from the Danish population was 1.2 times greater than that of ticks from Russia. Females of the species studied and specimens from all study areas were more active than all other stages of development. The locomotor activity of both adult and immature I. ricinus that were infected with Borrelia burgdorferi sensu lato was suppressed when compared with uninfected specimens. The locomotor activity of I. persulcatus females infected by borreliae with exoskeleton anomalies was 1.3 times greater (P<0.05) than that of infected ticks without anomalies. Our data showed that infected females with exoskeleton anomalies could crawl faster on a human and reach uncovered parts of the body that are vulnerable for attachment and feeding. A study of locomotor activity and questing behaviour may be useful for comparing the risk for different tick species and populations to transmit tick-borne pathogens.Successful transmission of pathogens to humans depends on the behaviour of the vectors inclusive of their activity, mobility, and ability to quest for prey and attack hosts. Ixodid ticks of different species and populations within species differ in their abilities to transmit pathogens and for successful maintenance of disease foci. For example, the ticks Ixodes persulcatus Schulze, 1930, are more effective vectors of pathogens than Ixodes ricinus (L., 1758) (Alekseev and Dubinina 1994, Kovalevskii andKorenberg 1995). Methods used to estimate tick behaviour vary and are generally directed to ascertain locomotor activity, which implies an orientation to physical parameters of the environment such as relative humidity, temperature and light and behaviour during questing for a host.The predominant behaviour of I. ricinus is the tendency of the tick to ascend vegetation during the day and descend at night (McLeod 1935, Lees and Milne 1951, Arthur 1962. A general survey of unfed I. persulcatus was given by Babenko (1985) and Babenko et al. (1985). However the work of Okulova (1978) may be the most interesting example of the orientation behaviour of unfed ticks as related to the physical parameters. Okulova (1978) has presented data on the vertical and horizontal movements of questing taiga ticks, which were studied in a forest environment under naturally occurring temperature and relative humidity. Adults climbed up the aconite and fern stems to a maximum height of 80 cm...

Four different alleles in the nymphal Ixodes ricinus were found for the Malate Dehydrogenase enzyme (MDH). The allele frequency of the MDH genotypes in nymphal I. ricinus was observed to change during the day. Some genotypes were present in the morning, but not in the afternoon and evening. The physiological age of the nymphs was also determined. No significant correlation could be found between physiological age and genotypes. Based on the results it must be anticipated that the comparability of tick samples not only differs in quantity but also in quality for various hours, but not necessarily for various months. Therefore isoenzyme analysis of nymphs at least as regards the MDH alleles appears to be a convenient biological tool to analyse differences in host seeking behaviour.