Abundance of Ixodes trianguliceps (Acari, Ixodidae) in the Mid-Boreal Subzone of Karelia (Russia)

Ixodes (Exopalpiger) trianguliceps Birula, 1895 is a three-host tick with a primitive non-nidicolous type of parasitism. They encounter hosts outside nests or burrows—in the topsoil, floor, or the ground vegetation layer. The principal hosts for the ticks in all active phases are small mammals of the orders Eulipotyphla and Rodentia. At present, I. trianguliceps has a wide Palearctic distribution. Russian Karelia, where the tick occurs throughout the territory, is the northern part of the species’ range. The aim of this study was to estimate the abundances of I. trianguliceps larvae, nymphs, and adults that parasitize small mammals in mid-boreal Karelia. Surveys were carried out at a field research station of the Institute of Biology of the Karelian Research Centre of the Russian Academy of Sciences (Vlg. Gomselga, Karelia, N 62.068°, E 33.959°) between 2011 and 2024. A total of 2237 host individuals were captured, yielding 1165 larvae, 378 nymphs, and 24 adults of I. trianguliceps. Tick larvae parasitized small mammals in all the surveyed months. Nymphs were primarily collected between May and September, and adult I. trianguliceps—in July. During a season, small mammals provide nourishment for 642 larvae, 133 nymphs, and 6 females of I. trianguliceps per average hectare of the study area. Our estimates of the tick abundance can be used to assess the species’ survival rates over the life cycle. They indicate that the survival rates of I. trianguliceps through phase transitions in mid-boreal Karelia will be around 27% (clutch to larvae), 21% (larvae to nymphs), and 9% (nymphs to adult ticks). The low abundance of adult ticks may be due both to the small share of the species’ most favored habitats in the study area as well as to the fact that Karelia is at the northern periphery of the I. trianguliceps distribution range.