On the Distribution of the Castor Bean Tick Ixodes ricinus (Acarina, Ixodidae) in the Republic of Karelia, Russia

The ixodid ticks Ixodes ricinus (L., 1758) and I. persulcatus Sch., 1930 are the main vectors of tick-borne encephalitis and Lyme disease pathogens in Karelia. Since the outlines of the natural foci of these infections fully coincide with the distributions of the taiga and castor bean ticks, research into the patterns of their spatial distribution is of high relevance. The results of long-term transect surveys, presented herein, demonstrate changes in the distribution and abundance of I. ricinus since the 1950s. The overall geographic distribution of I. ricinus in Karelia is presently characterized by reduction of its range, non-uniform distribution, and low numbers. In general, the optimal conditions for this species are restricted to the southwestern agroclimatic zone (mostly the territory of Lakhdenpokhskii District), where it also occurred in the past. Changes in the occurrence of I. ricinus can be observed both in its non-shared habitats and in the areas which the species inhabits sympatrically with the taiga tick I. persulcatus . The areas occupied by I. ricinus alone in the western part of the southern agroclimatic zone and also the sympatric areas in the central part of this zone have shrunk, while the sympatric areas in the southwestern zone (Pitkyarantskii and Sortavalskii districts) have grown.