Survival and Development of Ixodes scapularis (Acari: Ixodidae) Under Various Climatic Conditions in Ontario, Canada

Abstract

Distribution of the blacklegged tick, Ixodes scapularis Say, is poorly defined in Ontario. An endemic population is known on Long Point peninsula, Lake Erie, Ontario, but I. scapularis adults have also been collected from other localities within the province. To test the hypothesis that distribution of the blacklegged tick is limited by cold climatic extremes, 35 fed female, 70 unfed adult, and 70 unfed nymphal I. scapularis were held in containers within four natural habitats on Long Point (42 degrees 36' N; 80 degrees 5' W) and at northern localities near Ottawa (45 degrees 27' N; 75 degrees 42' W), Hearst (49 degrees 40' N; 83 degrees 41' W), and Kenora (49 degrees 47' N; 94 degrees 29' W), Ontario, from early December 1991 until May 1993. At the northern localities, 84.8 and 30.5% of fed females and unfed adults survived overwinter, respectively. On Long Point, 56.4% of fed females and 23.6% of unfed adults successfully overwintered. Longevity of fed females and unfed adults was increased by > 2 mo at the northern localities compared with Long Point, although survival rates for unfed nymphs at the northern sites and on Long Point were similar. Females within the four habitats on Long Point, and at Kenora and Ottawa, laid eggs from late April to mid-May, whereas eggs were deposited in late June at Hearst. Emergence of larvae from eggs began in late July or early August on Long Point and at Ottawa. Larvae were first observed in early October at Kenora, and no larvae emerged during 1992 at Hearst. Some eggs that overwintered during 1992-1993 at the northern sites were viable; however, hatching rate was < 10%. The minimum duration of the life cycle of I. scapularis is extended when ticks are introduced into regions of the province with seasonal degree-day accumulations lower than those observed on Long Point. Delays in deposition of eggs and emergence of larvae at Hearst and Kenora were likely a result of insufficient accumulation of degree-days above threshold temperatures for development in 1992. Though some eggs can overwinter successfully, suggesting that latitude-related reduction in seasonal temperature may not limit distribution of this tick in Ontario, hatchability was low. This factor, combined with innate incremental mortality at each instar, difficulty in finding a mate, and low density of medium to large mammal hosts for adults, may mitigate against establishment of I. scapularis by introduction of individual ticks into certain northern regions.

Lyme Disease Propelled by Borrelia burgdorferi-Infected Blacklegged Ticks, Wild Birds and Public Awareness ─ Not Climate Change

“…In our overwinter experiment, we observed that when warm weather melted the snow cover in February, overwinter survival dropped to 33%. Our findings are consistent with other researchers who found that overwinter survival of I. scapularis females at Long Point, Ontario decreased due to lack of snow cover [21]. As well, Brunner et al found that blacklegged ticks are sensitive to cold threshold temperatures [22].…”

Human Risk of Infection with Borrelia burgdorferi, the Lyme Disease Agent, in Eastern United States

“…Extreme winter temperatures can limit the northern distribution of ticks by directly killing the ticks, 43,50 inhibiting host-seeking activity, 44,46,47 or limiting the availability of hosts. 51 The high rate of fall cooling can also affect tick population dynamics by limiting the time available for larvae to find a host in the fall, thus entering diapause unfed, 52 which potentially increases their mortality rate. 52 On the other hand, high rates of spring warming may have an opposite effect, because it would result in faster accumulation of degree-days for development, potentially leading to earlier egg deposition and larval emergence.…”

Incidence and hospitalisation rates of Lyme borreliosis, France, 2004 to 2012

“…Winter survival depends on minimum temperatures, duration of exposure to cold, the tick's developmental stage and feeding status. Even if the tick survives the winter, further ability to undergo metamorphosis the following spring depends on the length and magnitude of exposure to the cold (Lindsay et al, 1995). Nymphs and adults may resist freezing temperatures well below -7 ºC, whereas eggs and larvae, especially if fed, are slightly more sensitive to the cold (Table 4) (Balashov, 1972;Daniel et al, 1977;Gray, 1981).…”