Cold Hardiness Characteristics in a Strain of the Predatory Mite Euseius (Amblyseius) finlandicus (Acari: Phytoseiidae) from Northern Greece

The supercooling points (SCP) of immature stages and adults as well as survival of adult females after exposure to subzero temperatures were studied in a strain of the predatory mite Euseius finlandicus (Oudemans) from northern Greece. The mean SCP of eggs was −27.6°C. The mean SCPs of different immature stages fed on pollens of Papaver rhoeas L. or Typha sp. enriched with β-carotene were similar and varied from −21.1 to −24.7°C. The mean SCPs of diapause females acclimated for 2 wk at 5°C or not acclimated, nondiapause females and males fed on pollens of P. rhoeas and Typha sp. were similar and varied from −22 to −24.3°C. When groups of diapause females were exposed temporarily to different subzero temperatures, the temperature-mortality curve followed the distribution of the SCPs, which indicates that the SCP is the lower limit of survival. More than 80% of the diapause females died when exposed for 20 min to −15°C, a temperature well above the SCP which indicates that they suffered prefreeze mortality. They survived considerably longer durations of exposure to −15°C after a prior acclimation for 2 wk at different low temperatures. After certain acclimation treatments, diapause females that survived exposure to −15°C laid a similar number of viable eggs as those not exposed to subzero temperatures, which indicates that cold stress may not affect fecundity.