Carryover Effects of Thermal Conditions on Tick Survival, Behavior, and Simulated Detectability

Carryover effects occur when environmental history of an organism influences its behavior, fitness, and population dynamics. Carryover effects have received some attention in the field of vector-borne disease ecology but are understudied in the context of ticks and tick-borne pathogen transmission where they may influence tick-host contact, pathogen transmission, and tick surveillance. Using controlled lab studies, we investigated how recent thermal history affects mortality and activity of adult Amblyomma americanum, an emerging vector of human and animal pathogens. To characterize thermal carryover effects on tick detection, we used our laboratory data to parameterize a simulation of tick trapping in the field. Ticks exposed to warm conditions for 4 weeks subsequently exhibited an increased mortality rate and heightened activity levels (as measured by time spent moving and distance moved in 24 h) that declined over time compared to ticks with cool thermal histories that had a lower mortality rate and maintained steady activity levels over time. Past thermal conditions had carryover effects on tick detection with simulated trapping. Early in the simulation (Days 0-8) ticks with a warm history were detected at higher rates due to carryover effects on tick movement. Later in the simulation (Days 10-20) ticks with a cool history were detected at higher rates due to a combination of carryover effects on movement and mortality. These findings demonstrate short-term thermal carryover effects on adult A. americanum that have implications for tick surveillance and tick-borne pathogen risk.