The influence of temperature on growth, reproduction and survival of the American dog tick, Dermacentor Variabilis (Say) in Southwestern Nova Scotia

The relationship between development, reproduction, survival and constant and field temperatures is described for the life stages of the American dog tick, Dermacentor variabilis (Say). For all experiments wild ticks and wild hosts were used. In this manner biases that might occur in laboratory-cultured ticks or in unnatural hosts were avoided. Development time of eggs, larvae and nymphs decreased with an increase in temperature for each life stage. The lower temperature threshold of development for eggs was 12.95°C, for larvae was 12.28°C, and nymphs was 11.43°C. The pattern of daily oviposition rates varied in shape and magnitude of peaks depending on the temperature at which the ticks were kept. Average peak daily oviposition was as high as 528 eggs/female on the 3rd day of oviposition and as low as 79 eggs/female on the 32nd day of oviposition for ticks kept at 29.7°C and 15°C, respectively. Towards the end of the oviposition period, egg viability was reduced. Larvae and adults were the main overwintering stages in southwestern Nova Scotia. A few adults can survive two winters. Larval and nymphal survival during development decreased at the upper and lower extremes of the 10-34°C range. Nymphs fed on Lepus americanus (Erxleben) weighed less and had a lower survival rate than those fed on four other small mammal species. The mean freezing point for D. variabilis adults was -11.9°C and for larvae was -21.7°C. From the field survival experiments and development rates determined in the laboratory the life cycle of D. variabilis was determined to normally take 2 years to complete in, southwestern Nova Scotia.