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Prior to its identification as the vector of Lyme borreliosis spirochaetes in Europe in 1983, interest in Ixodes ricinus(L.) was moderate and mainly concerned the transmission of pathogens to farm animals and of tick-borne encephalitis virus to humans. The situation now is very different, and more papers have been published on I. ricinusthan on any other ixodid tick species. However, this large literature is scattered and in recent years has become dominated by the molecular detection and characterization of the many pathogens that I. ricinustransmits. Several decades have now elapsed since a review addressing its basic biology and ecology appeared, and the present publication seeks to present basic aspects of its biology and ecology that are related to its role as a vector of disease agents, including its life cycle, feeding behaviour, host relations, survival off the host, and the impact of weather and climate.

Four members of the Ixodes ricinusspecies complex, Ixodespacificus, Ixodespersulcatus, Ixodesricinusand Ixodesscapularis, have, between them, a worldwide distribution within the northern hemisphere. They are responsible for the transmission of several animal and human pathogens, including the causal agents of Lyme borreliosis, tick-borne encephalitis, human granulocytic anaplasmosis and human babesiosis. Despite the importance of these ticks as vectors, the knowledge and understanding of the role that diapause plays in their complex life cycles are confused and incomplete. In view of the continuing geographic spread of these tick species, as well as the effects of climate change on vector-borne diseases, it is timely to encourage research on diapause phenomena to improve understanding of their biology and of pathogen transmission dynamics. In our review we seek to clarify thinking on the topic and to address gaps in our knowledge that require the attention of researchers.

This is the first study to determine the density of questing Ixodes ricinusin northern Norway. It was performed at two sites in Brønnøy, which has been known for its tick permissive habitats for decades and is one of the northernmost habitats with an abundant I. ricinuspopulation in the world. From April to November 2011, all stages of host-seeking I. ricinuswere collected from the two sites. The overall prevalence of nymphs infected with Borrelia burgdorferisensu lato was 21% and that of adult ticks 46%. The rates of the genospecies Borrelia afzelii, Borrelia garinii, and Borrelia valaisianawere similar to findings in most other studies in Scandinavia, with B. afzeliiby far the most prevalent at 76%. The high Borrelia-infection prevalence in ticks from Brønnøy may explain the high incidence rate of reported Lyme borreliosis in the municipality.

•The distribution of ticks in Ireland chiefly coincides with historical high incidence areas of bovine babesiosis.•The infection rate of questing nymphs with B. burgdorferis.l. has remained stable over the last 3 decades.•The prevalence of the various genospecies has remained essentially unchanged since the 1990′s.•The risk of contracting LB from a tick bite remains low even in woodlands where tick abundance is comparatively high.