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19 October 2020 Supercooling Points of Adult Dermacentor variabilis (Acari: Ixodidae) From a Population Near the Northern Distribution Limit
Matthew E. M. Yunik, Neil B. Chilton
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The northern distributional limit of Dermacentor variabilis Say, the American dog tick, is expanding in Saskatchewan and Manitoba (western Canada). The ability of D. variabilis to continue to expand its range northwards will depend upon the ability of individuals within populations at the species distributional edge to withstand very low temperatures during winter. One component of cold hardiness is the supercooling point (SCP), the temperature below 0°C at which an individual freezes. In this study, the SCP was determined for 94 questing D. variabilis adults (44 females and 50 males) from an established population near Blackstrap Provincial Park in Saskatchewan. SCP values ranged from –18.2 to –6.7°C, with a median of –13.3°C. This suggests that host-seeking D. variabilis adults differ in their ability to survive exposure to subzero temperatures, for at least a short period of time, without freezing. The distribution of SCPs was bimodal, but there was no significant difference in SCP values between female and male ticks, and no relationship between SCP and tick body weight. It remains to be determined what factors contribute to the variation in SCP values among questing D. variabilis adults.

© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail:
Matthew E. M. Yunik and Neil B. Chilton "Supercooling Points of Adult Dermacentor variabilis (Acari: Ixodidae) From a Population Near the Northern Distribution Limit," Journal of Medical Entomology 58(2), 961-964, (19 October 2020).
Received: 30 June 2020; Accepted: 16 September 2020; Published: 19 October 2020

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cold hardiness
Dermacentor variabilis
supercooling point
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