Effects of prolonged exposure to low temperature on eggs of the brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae)

The widespread geographical distribution of the brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae) is related to the cosmopolitan distribution of its primary host and to its adaptability to different environments, under variable climate conditions. Field studies have suggested that temperature is the most important factor driving the population dynamics of this tick species. In order to investigate the effects of prolonged exposure to low temperature on eggs of R. sanguineus, nine groups (II-X) of five egg batches each were maintained at 8+/-2 degrees C (70+/-10% RH, and scotophase) for 15, 30, 45, 60, 75, 90, 105, 120, and 135 days. One group (group I) was maintained in the incubator (26+/-1 degrees C, 70+/-10% RH, and scotophase) and used as control. The mean egg incubation period from group I was 11.6+/-0.5 days, with an egg hatch rate of 99.5+/-0.5%. Conversely, no egg hatched at 8 degrees C. Exposure to cold showed a strong positive correlation with egg incubation period (r=0.99) as well as a strong negative correlation with egg hatch rate (r=-0.95) and larval longevity (r=-0.99). Overall, the present results points out that R. sanguineus eggs are sensible to prolonged exposure to low temperature, which is definitely a major limiting factor for the establishment of populations of this tick in cold temperate regions.