Established populations of Ixodes silvanus (Acari: Ixodidae) in the Chaco Serrano, Argentina.

The aim of the study was to report the occurrence of Ixodes silvanus outside its distribution range, in the Chaco Serrano vegetation unit of the Chaco Phytogeographic Province, central Argentina. Ticks were collected from vegetation and on birds between November 2021 and December 2023. A possible seasonal activity was observed in the immature stages of I. silvanus, with larvae in autumn-winter and nymphs in spring-summer, consistent with a behavioral diapause. A total of 937 ticks were identified as I. silvanus and confirmed molecularly, 741 host-seeking and 196 parasitizing 49 passerine birds (of 9 species, 6 genera and 5 families). All host-seeking ticks were found in leaf litter in forests dominated by the invasive tree Ligustrum lucidum, suggesting a possible link between environmental changes and the establishment of I. silvanus in this region. The prevalence of I. silvanus on birds was 27.4%, with significant participation of the Turdus genus and new host associations documented. The findings suggest that I. silvanus may be expanding its range, potentially facilitated by environmental modifications, the movement of austral migratory birds (Turdus nigriceps, Synallaxis frontalis and Zonotrichia capensis), and the range expansion of other bird species (Turdus amaurochalinus, Turdus chiguanco and Turdus rufiventris). Therefore, I. silvanus may represent a biological invasion and a potential threat to wild bird populations as a vector of pathogenic microorganisms. Future studies are required to determine the implications this could have.