Range Expansion ofDermacentor variabilisandDermacentor andersoni(Acari: Ixodidae) Near Their Northern Distributional Limits

Abstract

Distributional ranges of the ticks Dermacentor andersoni Stiles and Dermacentor variabilis (Say) in the Canadian Prairies were determined by passive surveillance and active collection. These findings were compared with historical records of both species, particularly in the province of Saskatchewan, where the northern distributional limits of both tick species occur. Before the 1960s, D. variabilis and D. andersoni were allopatric in Saskatchewan; however, since then, the distribution of D. variabilis has expanded westward and northward. Although the range of D. andersoni has remained relatively stable, range expansion of D. variabilis has resulted in a zone of sympatry at least 200 km wide. Twenty-nine species of mammals and three species of birds were identified as hosts for different life stages of these ticks.

The Biological Survey of Canada: A Personal History

“…In Saskatchewan, populations occur sporadically in central and western regions of the province. The eastern limit of the range of the tick is approximately 105°W longitude (Wilkinson 1967), where it now overlaps with the expanding westward spread in the distribution of D. variabilis (Dergousoff et al 2013). In Alberta, populations of D. andersoni are most abundant in the southeastern portions of the province (Brown 1944).…”

“…It is widely distributed and often abundant in southern Manitoba into northwestern Ontario, as well as southeastern Saskatchewan. The American dog tick has expanded its range in Manitoba and Saskatchewan, and is established considerably further north and west than 50 years ago (Dergousoff et al 2013).…”

“…In addition, ranges of many species of ticks are changing rapidly (e.g., Dergousoff et al 2013) and government policies regarding ticks and tick-borne pathogens are being modified. We hope this handbook will serve to stimulate further investigations in these fields.…”

A Novel Rickettsia Species Detected in Vole Ticks (Ixodes angustus) from Western Canada

“…Both D. andersoni and D. variabilis are also known vectors of R. rickettsii, the causative agent of Rocky Mountain spotted fever (16). All of these species of Ixodes and Dermacentor use rodents and/or insectivores as hosts for some part of their life cycle (12,17).…”

“…R. canadensis has been reported from several tick species (i.e., Haemaphysalis leporispalustris, D. andersoni, D. variabilis, and Ambylomma americanum) in Canada and the United States (3). The distributional range of I. kingi in western Canada overlaps that of D. andersoni and D. variabilis and several species of Ixodes, including the sculptured tick, I. sculptus, and the vole tick, I. angustus (17)(18)(19)(20). Although I. angustus has been implicated as a vector of pathogenic bacteria, such as Borrelia burgdorferi (21), there are no reports of the presence of Rickettsia in this tick species or in I. sculptus.…”