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1 September 2012 Overwintering Survival of Nymphal Ixodes scapularis (Acari: Ixodidae) Under Natural Conditions
Jesse L. Brunner, Mary Killilea, Richard S. Ostfeld
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Blacklegged ticks (Ixodes scapularis Say) are exquisitely sensitive to very cold and dry conditions. For this reason it has long been assumed that climatic differences among locations and within microhabitats have a strong influence on variation in their survival over winter. This assumption, however, rests largely on laboratory exposures and on broad-scale associations between climatic variables and the observed distributions of ticks. We present the results of a study of the overwintering survival of I. scapularis nymphs in their natural environment from October through May in two locations in New York State using a repeated sampling strategy to determine when mortality occurred, and whether those events coincide with extreme conditions. We then fit these data to a simple, flexible statistical model in which the hazard of mortality varies with measurable conditions, here minimum daily temperature and mean daily relative humidity. Regardless of winter conditions, >80% of ticks survived at both sites. A model with constant hazard (i.e., independent of temperature and humidity) was best supported by the data. Although models with hazard increasing at temperatures below 0 deg C and at >90% relative humidity provided slightly better fits to the data, these models were less parsimonious. These results weaken the expectation that cold-related overwintering mortality necessarily plays a major role in restricting populations of these ticks and thus, risk of tick-borne zoonoses.

© 2012 Entomological Society of America
Jesse L. Brunner, Mary Killilea, and Richard S. Ostfeld "Overwintering Survival of Nymphal Ixodes scapularis (Acari: Ixodidae) Under Natural Conditions," Journal of Medical Entomology 49(5), 981-987, (1 September 2012).
Received: 15 March 2012; Accepted: 1 June 2012; Published: 1 September 2012

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Ixodes scapularis
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