Abstract
Simple SummaryA tick’s ability to survive in cold, harsh winter conditions is influenced by numerous factors including the tick species, the variability in temperature, and the suitability of the overwintering habitat (containing insulation to retain heat). We investigated the influence of elevation and insulation coverage on the survivability of three newly invading ticks, Amblyomma americanum, Amblyomma maculatum, and Haemaphysalis longicornis and one native tick species already established in southwestern Virginia, Dermacentor variabilis. For the invasive species, we found that life stage was the only determining factor in survival for Haemaphysalis longicornis and Amblyomma americanum, whereas, Amblyomma maculatum survival was largely influenced by insulation coverage. Dermacentor variabilis survivability was not affected by elevation or insulation coverage in this study. Ticks are susceptible to environmental conditions and, to ensure survival during winter conditions, they adopt a wide variety of physiological and behavioral adaptations including utilization of a suitable niche with insulation (e.g., leaf coverage). To investigate the potential overwintering survival of three tick populations emerging within Appalachian Virginia (Haemaphysalis longicornis, Amblyomma americanum, and Amblyomma maculatum), both a laboratory experiment assessing super-cooling points and a two-factor (elevation and insulation coverage) field experiment assessing overwintering survivability were conducted across a natural southwestern Virginian winter (2020–2021). Dermacentor variabilis adults were included in this study as an example of a well-established species in this region known to overwinter in these conditions. Our study indicated that A. americanum and H. longicornis wintering tolerance is based on life stage rather than external factors such as insulation (e.g., leaf litter) and elevation. Amblyomma maculatum was more likely to survive without insulation. The ability to withstand the extreme temperatures of new regions is a key factor determining the survivability of novel tick species and is useful in assessing the invasion potential of arthropod vectors.
Highlights
Initial detections of A. maculatum, A. americanum, and H. longicornis have been made in counties of the western region of the Commonwealth and the New River Valley in recent years [10,11,12], but there is a paucity of knowledge in terms of their ability to tolerate Appalachian winter conditions, and we argue that the existing literature on the climate tolerance of these species does not elucidate how they might survive in this mountainous region of Virginia
A. americanum depended on an interaction between leaf litter and elevation (odds ratios: leaves vs. no leaves for 2000 vs. 1000 ft: 1.9 (0.0 to 114.9), p = 0.91; leaves vs. no leaves for
Our results showed that three emerging tick species in southwestern Virginia, H. longicornis, A. americanum, and A. maculatum, as well as the native tick species D. variabilis, had varying survival rates, and that leaf insulation and elevation are not necessarily crucial determinants of survival
Summary
The majority of ixodid ticks spend most of their life free-living within the environment, only emerging from their microhabitats in the pursuit of a host bloodmeal. Due to the need for long-term suitable habitat between bloodmeals, hard tick survival is heavily dependent upon the adoption of physiological and behavioral adjustments, during overwintering. Overwintering is the ability of a tick to survive free in the environment while being subject to local climatic conditions and weather during the winter. This includes searching for and obtaining a suitable habitat with an insulating layer (e.g., leaves and stones), entering diapause, or increasing their concentration of cryoprotectants [1]. In a study published by Linske et al [6] investigating the overwintering survival of I. scapularis in the northeastern
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