Assessment of the risk of infestation of pastures by Ixodes ricinus due to their phyto-ecological characteristics.

This study aims to assess the relationships between the phyto-ecological characteristics of grazing pastures and their risk of being infested by the hard tick Ixodes ricinus. To that purpose, 128 pastures belonging to 20 dairy farms were observed from April to July 1994. The farms were located in western France. Assessment of the tick population was made by four monthly, blanket-dragging sessions. The average infestation rate was 40.2%. Six types of pastures were identified according to their basic phyto-ecological characteristics using a factorial analysis of correspondences followed by a hierarchical ascending classification. These identified types were significantly related to the infestation rates, thereby making it possible to provide a predictive value in risk assessment. The infestation rates were high (96% on average) in two types of pastures characterized by their proximity to woods, and low (13%) in two other types characterized by seeded grass species located at some distance from woods, and intermediate (39% on average) in the last two types.