Seasonal and diel environment effects on host-seeking behaviour in the European tick vector, Ixodes ricinus

Patterns of arthropod vector abundance and activity are key determinants of biting risk, and thus the risk of vector-borne pathogen transmission. Ticks are important vectors of animal and human pathogens worldwide. Their host-seeking activity (questing) directly influences the risk of exposure to ticks and their pathogens, but the drivers of this behaviour are poorly understood. Here, the concurrent seasonal and diel variation in Ixodes ricinus questing behaviour was investigated, for the first time, by blanket dragging every four hours over a 24-hour sampling cycle each month, from January to December 2022. A predominantly nocturnal questing activity pattern was observed, moderated by seasonal moisture availability, being most evident in months with high saturation deficit. Generalised Linear Mixed Modelling predicted that the density of questing nymphs was positively associated with darkness, and negatively associated with saturation deficit, which interacted with soil temperature. The observed seasonal questing patterns are largely consistent with published data; however this is the first study to highlight the importance of nocturnal feeding at periods of high saturation deficit. These commonly overlooked daily rhythms and environmental moderators of tick behaviour have important implications for assessing the relative risk of exposure to ticks and their pathogens for different hosts, and for estimating abundance in scientific research and surveillance.