Abundance of Ixodes ricinus and influencing factors in northern Germany during 2021-2022

Abstract text

Ixodes ricinus is the main vector of tick-borne pathogens in Europe. Although there have been many studies on this tick species, the driving factors of its local abundance are not yet fully understood. In northern Germany, tick abundance has been little studied, as compared to southern parts of the country. In this ongoing study, we aim to assess questing tick abundance and ecological correlates across northern Germany. From April to July of 2021 and 2022, i.e. during the main I. ricinus activity period, 43 sites in 13 areas were sampled monthly by the flagging method. Associations with habitat characteristics and climate data were analysed via mixed modelling. Approximately 25,000 I. ricinus/inopinatus specimens were collected. The average density of questing nymphs ranged from 0.9/100 m² to 227.4/100 m² depending on the studied site, with a mean number of adult ticks from 0.4 to 29.5/100 m². Altogether, higher questing tick densities were observed in 2021 (ø 1.0-359.0 nymphs/100 m²) than in 2022 (ø 0.8-149.3 nymphs/100 m²), but there were differences among areas and sites. Significant correlations of nymph density with forest type, temperature and precipitation were observed. The number of frost days in the preceding winter was significantly associated with nymph density in broadleaved and coniferous, but not in mixed and inner-urban forests. Monitoring of these comparatively high questing tick densities will be continued in this so far neglected geographic area in 2023.