title: Cold hardiness and influences of hibernaculum conditions on overwintering survival of American dog tick larvae.
abstract: Understanding how ticks survive the multitude of stresses experienced during winter is integral to predicting population dynamics and transmission of tick-borne pathogens. The American dog tick (Dermacentor variabilis), a predominant vector of Rocky Mountain spotted fever, overwinters in any of its post-egg life stages. In this study, we characterized the cold tolerance of larval D. variabilis and examined the effect of various acclimatory conditions on cold hardiness. Cold-shock survival during 2h exposure to various subzero temperatures was assessed and a lower lethal temperature of -20°C and a 50% mortality temperature near -16°C was established. Larvae exposed to -5°C showed high survival (∼70%) after 14 d and near 50% for up to 56d at -5°C. Larvae cycled between supra- and subzero temperatures showed better long-term survival than at constant -5°C. The temperature of crystallization (Tc) was ∼-23°C and no larvae survived freezing after reaching their Tc. Larvae exposed to inoculative freezing survived brief, mild treatments (70% survival of -5°C for 2h) but survival was reduced compared to larvae cooled in the absence of ice. Reduced photophase, rapid cold hardening, dehydration, and long-term thermal acclimation all improved larval cold hardiness to varying degrees. Survival data were compared to measurements of hibernacula conditions, and we conclude that larvae face little threat from cold-induced mortality but inoculative freezing does pose a risk, and the geographic distribution of D. variabilis is only minimally influenced by the ability of larvae to survive low temperature exposure.
authors.affiliation: Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, 45221, United States. Electronic address: rosendaw@uc.edu.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Rosendale
authors.affiliation: Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, 45221, United States.
authors.forename: David W
authors.initials: DW
authors.lastname: Farrow
authors.affiliation: Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, 45221, United States.
authors.forename: Megan E
authors.initials: ME
authors.lastname: Dunlevy
authors.affiliation: Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, 45221, United States.
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Fieler
authors.affiliation: Department of Biological Sciences, University of Cincinnati, Cincinnati, OH, 45221, United States.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Benoit
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003080:Cold Temperature; D003870:Dermacentor / Q000502:physiology*; D004777:Environment; D005260:Female; D007814:Larva; D009820:Ohio; D012621:Seasons; D013997:Time Factors
keywords: Acclimation; Cold hardiness; Dermacentor variabilis; Photoperiod; Rapid cold hardening