Long-term dynamics of Ixodes persulcatus (Acari: Ixodidae) abundance in the north-west of its range (Karelia, Russia).

The article presents the results of long-term observations of variations in the abundance of Ixodes persulcatus, carried out since 1982, in the middle taiga subzone of Karelia. Adult questing ticks were collected from vegetation following standard flagging procedures. The time series was evaluated by singular spectrum analysis. Correlation coefficients were calculated for the observed tick abundances and meteorological data (mean daily air temperature and precipitation) for the current year and preceding years. Analysis of the time series revealed the trend and harmonic components with periods of 8, 2.5 and 4 years. Around 83% of the total variance is explained by the first principal component, which governs the general vector of change-a gradual reduction in I. persulcatus abundance from 2003 to 2017. Correlations between tick abundance and climatic indices were observed in all years and were associated with both temperature and precipitation. The greatest number of significant coefficients was obtained for correlations between tick abundance and weather conditions in the preceding season. An equation was suggested where tick abundance is described by a linear function with four variables: mean air temperature in April and July, total precipitation in February, and annual number of days with temperatures above 5 °С. Thus, the observed long-term dynamics are characterized by the following key patterns: a sharp population rise early in the 2000s, some recent decline (stabilization) of the abundance, the presence of quasi-periodic cycles, and a close correlation between tick abundance and climatic variables.