Changes in population abundance of adult Dermacentor reticulatus (Acari: Amblyommidae) in long-term investigations in eastern Poland.

Investigations into the abundance of adult D. reticulatus in relation to the effect of climatic conditions (temperature, humidity) on host-seeking behaviour were conducted during the autumn (September-October) and spring (May) activity peaks in 2008-2009 in eastern Poland (51°25'N). The study was conducted in the same habitat where similar examinations were performed in 1999-2000. A comparative analysis revealed that the abundance of D. reticulatus had almost doubled within 10 years. Analysis of data on the humidity and temperature conditions prevailing during tick collection, and on tick abundance in the respective study periods in 1999-2000 and 2008-2009, as well as absence of climatic changes over many years, indicate that the increase in the numbers of ticks may have been a result of a multitude of other factors, e.g. weather or environmental conditions favourable for ticks and their hosts. The substantial differences in D. reticulatus abundance observed during the autumn activity peak (an increase from 126 and 128.6 specimens per collection in 1999 and 2000, respectively, to 247.3 in 2008) demonstrate the considerable effect of the biotic and abiotic conditions prevailing during the development of young and adult stages on the abundance of this tick species. The activity of adult D. reticulatus ticks in the autumn was 2.7-fold higher in comparison to that observed during the spring collection; the difference was statistically significant (p<0.0001). Females dominated in both seasonal activity peaks. The ratio between females and males during the spring and autumn peaks was 3.31:1 and 1.05:1, respectively. The increase in the abundance of the D. reticulatus population implies a higher risk of transmission of tick-borne diseases in the study area, and the necessity to develop and implement effective prevention methods and tick control programmes.