# Comparison of Hard Tick (Acari: Ixodidae) Fauna in Natural and Anthropogenic Habitats in Croatia

## TL;DR

This study compares hard tick species in natural and human-impacted habitats in Croatia, finding more diversity in human-impacted areas and new distribution records for some tick species.

## Contribution

The study provides new distributional records for tick species and reveals differences in tick seasonality and environmental correlations between natural and anthropogenic habitats.

## Key findings

- Hard tick species diversity was higher in anthropogenic habitats (8 species) compared to natural habitats (3 species).
- Ixodes ricinus was the most abundant species in both habitats but showed different seasonal patterns.
- New distribution records include Ixodes frontalis in eastern Croatia and Dermacentor reticulatus at 1000 m elevation.

## Abstract

In response to increasing global concern regarding the occurrence of hard ticks (Acari: Ixodidae) and tick-borne diseases, we investigated the diversity, structure and seasonal dynamics of hard tick fauna in natural habitats (NHs) (i.e., pedunculate oak, common beech and silver fir forest communities, 200–1000 m a.s.l.) and anthropogenically conditioned habitats (AHs) (i.e., orchards, grasslands, degraded forests, 150–250 m a.s.l.) in Continental Croatia (2019–2021, 2023–2024 yr.). Flag-dragging method was used to sample host-seeking ticks, resulting in the identification of 2726 specimens from AHs and 1543 hard ticks sampled in NHs. The AHs showed a greater species diversity, with eight tick species identified (Ixodes ricinus, I. frontalis, I. hexagonus, I. kaiseri, Haemaphysalis inermis, H. concinna, Dermacentor marginatus, D. reticulatus) compared to only three (I. ricinus, I. frontalis, D. reticulatus) in the NHs. The most abundant species in both environments was Ixodes ricinus, one of the major tick-disease vectors, which exhibited a bimodal seasonal activity in AHs and a unimodal pattern in NHs. Abundance of some species, such as Haemaphysalis inermis and Dermacentor reticulatus, showed a significant negative correlation with temperature and a positive correlation with humidity in AHs. Conversely, I. ricinus abundance in NHs was positively associated with temperature and negatively with humidity. The study also documented new distributional records, including I. frontalis in eastern parts of the country and D. reticulatus at a new elevation of 1000 m above sea level in Central Croatia. These findings contribute new data on the distribution and seasonality of medically important tick species, aiding in the identification of tick-risk foci and high-risk periods.

Due to the evident increase in tick-borne diseases worldwide, it is necessary to constantly update information on the distribution and zoonotic potential of hard ticks. We studied diversity, population structure, and seasonal dynamics of hard tick fauna, faunal similarity and the climate impact on tick occurrence in natural habitats (NHs) (forest communities) and anthropogenic habitats (AHs) (orchards, grasslands, degraded forests) in eastern and central parts of Continental Croatia. Host-seeking hard ticks were sampled by the flag-dragging method in lowland AHs (Bansko Hill (BH); 2023–2024 yr.) and in mountainous NHs (Medvednica Mountain (MM); 2019–2021, 2024 yr.). Overall, 2726 specimens belonging to eight hard tick species (Ixodes ricinus, I. frontalis, I. hexagonus, I. kaiseri, Haemaphysalis inermis, H. concinna, Dermacentor marginatus, D. reticulatus) were identified in AHs, while in NHs 1543 hard ticks, belonging to three species (I. ricinus, I. frontalis, D. reticulatus), were collected. The most abundant species in both habitat types (47.83% in AHs, 99.80% in NHs) was I. ricinus, showing unimodal seasonal activity within studied NHs and bimodal activity at AHs. Comparison of hard tick fauna in different habitats using the Sørenson index on BH and MM showed a high percentage of similarity (50.0–88.8). At AHs, a significant (p < 0.05) negative correlation was determined between the abundance (N) and the mean monthly air temperatures (°C) for H. inermis (r = −0.5931; p = 0.0421) and D. reticulatus (r = −0.6289; p = 0.0285), while their numbers positively correlated (r = 0.5551; p = −0.2667; r = 0.4430; p = 0.1492) with air humidity (%). In contrast, the number of sampled host-seeking I. ricinus ticks at natural forest habitats on MM was positively associated with air temperature and negatively with air humidity at elevations from 200 to 1000 m a.s.l. (r = −0.7684; p = 0.0259; at 200 m a.s.l.). Collected specimens of I. frontalis mark the first record for Osijek–Baranja County, while the sampled D. reticulatus on MM represents the first catch at 1000 m a.s.l. in Croatia. This new data on the distribution and seasonality of medically important hard tick species in Continental Croatia contributes to identifying tick-risk foci and high-risk periods.