Investigating the effect of climate on blacklegged tick phenology in Maine using long-term passive surveillance data

Climate change has significant impacts on vector biology, including altering their phenology. This can have significant implications for vector-borne disease risk by shifting the timing of host encounters and changing pathogen transmission dynamics. In addition, the effects of climate change differ along large-scale spatial gradients. Vector surveillance data can help tease apart effects of climate change and year-to-year weather variation by providing relative activity patterns across long-term temporal scales. However, the availability of these data can be limited due to technical limitations in surveillance efforts for certain species. The blacklegged tick, Ixodes scapularis, is the primary vector of Lyme disease and other tick-borne diseases in the Northeastern U.S. In Maine, blacklegged ticks were first reported in the 1980s and have since spread through the state, becoming established in the southern portion of the state by the mid-2000s while populations continue to grow and spread into inland and northern portions of the state. To investigate effects of climate change on tick phenology, we utilized passive surveillance data from ticks submitted by the public to statewide identification programs for > 30 years (1989-2024). We calculated yearly phenometrics (i.e. activity onset, offset, and peak) for submitted blacklegged tick nymphs and adults (both spring and fall curves) in different climate regions. We extracted relevant yearly climate variables for these regions, then analyzed whether tick activity changed over time and/or with climate. These results will provide important information on seasonal tick-borne disease risk at the northern part of their range.