SEASONAL OVIPOSITION AND TEMPERATURE REQUIREMENTS OF EGGS MAY LIMIT NORTHERN DISTRIBUTION OF EUROPEAN ARGAS REFLEXUS (ACARI, ARGASIDAE)

Seasonal reproduction and embryonic development was investigated in Ar gas reflexus (F.) throughout a 5-yr period. Ticks were kept in desicca tors at approximate to 76% RH at 2 experimental sites-an attic and an outdoor aviary-that provided a natural photoperiod and temperature. Ti ck oviposition was limited to the summer months (June through August) regardless of the year of investigation and of the seasonal time of ti ck feeding. Engorged female ticks entered diapause between late July a nd late August. Ticks that had already started oviposition, stopped at that time and continued in the following year without requiring anoth er 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 mort ality observed in the attic, where temperatures reached greater than o r equal to 45 degrees C. A. reflexus eggs showed a low level of cold t olerance. 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 approximate to 34 d. In the attic and the aviary, none of the A. reflexus eggs were able to overw inter successfully during any of the investigated winters, including c omparatively mild ones. The results strongly suggest that the temperat ure sum available for embryonic development in summer/autumn limits th e northern distribution of A. reflexus.