A mechanistic model explains variation in larval tick questing phenology along an elevation gradient

Area of Science:

• Ecology
• Epidemiology
• Entomology

Background:

• Tick-borne pathogens rely on tick life cycles, with larval and nymphal host-seeking timing influencing pathogen persistence.
• The phenology of the blacklegged tick (Ixodes scapularis) varies across its range due to climate and local adaptation.
• Understanding tick phenology is critical for predicting and managing tick-borne diseases.

Purpose of the Study:

• To test a mechanistic, temperature-driven model's ability to explain variations in larval Ixodes scapularis phenology.
• To isolate the effect of climate on tick phenology using an elevation gradient where local adaptation is minimal.

Main Methods:

• Collected Ixodes scapularis ticks over 7 years using drag-cloth sampling along an elevation gradient (>500 m) in western Vermont, USA.
• Compared the performance of a literature-parametrized, temperature-driven model against competing models in explaining observed phenological differences.

Main Results:

• Observed a shift in larval tick questing periods: late summer at low elevations and early summer at high elevations.
• The temperature-driven model successfully reproduced the observed elevation-dependent differences in larval tick phenology.
• The model demonstrated superior explanatory power compared to alternative models.

Conclusions:

• Validated a mechanistic model linking temperature to larval Ixodes scapularis phenology.
• This model provides a tool to understand how climate influences tick behavior and, consequently, tick-borne disease dynamics.
• Findings highlight the importance of temperature-driven phenology in the enzootic cycles of tick-borne pathogens.