Influence of weather on questing strategy by Amblyomma americanum nymphs

Abstract

Ticks are ectoparasites that feed exclusively on blood from vertebrate hosts using questing (host-seeking behaviors) strategies such as ambushing (sitting/waiting on vegetation for hosts to brush by) or active pursuit (chasing after hosts). Tick abundance is assessed with flagging/dragging and carbon dioxide (CO₂)-baited trap methods, which target ambushing and actively pursuing ticks, respectively. Many studies employ only one collection method; however, the lone star tick, Amblyomma americanum, uses both ambushing and active pursuit. Weather is an environmental factor whose effect on questing strategy remains unclear. We hypothesized that if A. americanum changes host-seeking behaviors in response to weather, then the success rate of collection methods will vary accordingly. Sampling events occurred 3 rounds in 3 plots within each of 14 sites—including Tyson Research Center—across St. Louis County, Franklin County, and Jefferson County, using both flagging/dragging and CO₂ traps (N=110). During each survey, we recorded temperature, relative humidity, wind speed, and cloud cover. Using generalized linear mixed models with a binomial distribution, we modeled the influence of weather variables on the probability of A. americanum, nymphs either ambushing or actively pursing hosts. Over the course of 4 months, we collected 2,255 A. americanum nymphs via flagging/dragging, and 1,682 via CO₂ traps. Saturation deficit, the “drying” power of the atmosphere, and visit round had the greatest influence on tick questing behavior. Active pursuit increased as saturation deficit increased, but ambushing increased over the questing season. Cloudy conditions promoted ambushing and sunny conditions promoted active pursuit. These results underscore how weather can confound tick population estimates due to variability in tick behavior. Future A. americanum studies should employ flagging/dragging and CO₂ traps simultaneously. As climate change extends tick questing seasons, understanding how weather influences tick questing strategies is crucial for accurate tick surveillance.

Keywords: Tick, Amblyomma Americanum, Public Health, Weather

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