Vectors of disease at the northern distribution limit of the genus Dermacentor in Eurasia: D. reticulatus and D. silvarum

The two ixodid tick speciesDermacentor reticulatus(Fabricius) andDermacentor silvarumOlenev occur at the northern distribution limit of the genusDermacentorin Eurasia, within the belt of 34-60 degrees N latitude. Whilst the distribution area ofD. reticulatusextends from the Atlantic coast of Portugal to Western Siberia, that ofD. silvarumextends from Western Siberia to the Pacific coast. In Western Siberia, the distribution areas of the twoDermacentorspecies overlap. Although the two tick species are important vectors of disease, detailed information concerning the entire distribution area, climate adaptation, and proven vector competence is still missing. A dataset was compiled, resulting in 2188 georeferencedD. reticulatusand 522D. silvarumlocations. Up-to-date maps depicting the geographical distribution and climate adaptation of the twoDermacentorspecies are presented. To investigate the climate adaptation of the two tick species, the georeferenced locations were superimposed on a high-resolution map of the Koppen-Geiger climate classification. The frequency distribution ofD. reticulatusunder different climates shows two major peaks related to the following climates: warm temperate with precipitation all year round (57%) and boreal with precipitation all year round (40%). The frequency distribution ofD. silvarumshows also two major peaks related to boreal climates with precipitation all year round (30%) and boreal winter dry climates (60%).Dermacentor silvarumseems to be rather flexible concerning summer temperatures, which can range from cool to hot. In climates with cool summersD. reticulatusdoes not occur, it prefers warm and to a lesser extent hot summers. Lists are given in this paper for cases of proven vector competence for various agents of bothDermacentorspecies. For the first time, the entire distribution areas ofD. reticulatusandD. silvarumwere mapped using georeferenced data. Their climate adaptations were quantified by Koppen profiles.