Seasonal Oviposition and Temperature Requirements of Eggs May Limit Northern Distribution of European Argas reflexus (Acari: Argasidae)

Abstract

Seasonal reproduction and embryonic development was investigated in Argas reflexus (F.) throughout a 5-yr period. Ticks were kept in desiccators at approximately 76% RH at 2 experimental sites--an attic and an outdoor aviary--that provided a natural photoperiod and temperature. Tick oviposition was limited to the summer months (June through August) regardless of the year of investigation and of the seasonal time of tick feeding. Engorged female ticks entered diapause between late July and late August. Ticks that had already started oviposition, stopped at that time and continued in the following year without requiring another blood meal. In the laboratory, A. reflexus eggs exhibited an upper lethal temperature (ULT50: 1-h exposure) of 44.1 degrees C (95% CL: 43.7-45.5 degrees C), which is in accordance with the increased egg mortality observed in the attic, where temperatures reached > or = 45 degrees C. A. reflexus eggs showed a low level of cold tolerance. Despite a supercooling point of approximately -25 degrees C, their lower lethal temperature (LLT50: 24-h exposure) was only -12.3 degrees C. Even at a typical winter temperature of 3 degrees C and 76% RH, 50% egg mortality occurred after only approximately 34 d. In the attic and the aviary, none of the A. reflexus eggs were able to overwinter successfully during any of the investigated winters, including comparatively mild ones. The results strongly suggest that the temperature sum available for embryonic development in summer/autumn limits the northern distribution of A. reflexus.