Rapid cold hardening in the western flower thrips Frankliniella occidentalis

A rapid cold hardening process is reported in first instar larvae of Frankliniella occidentalis. When larvae are transferred directly from 20 degrees C to -11.5 degrees C for 2 h there is 78% mortality, whereas exposure to 0 degrees C for 4 h prior to transfer to -11.5 degrees C reduces mortality to 10%. The response can also be induced by exposure to 5 degrees C for 4 h or by gradual cooling at rates between 0.1 and 0.5 degrees C min(-1). The acquired cold tolerance is transient and is rapidly lost (after 1h at 20 degrees C), Rapid cold hardening extends survival times at -11.5 degrees C and depresses lethal temperatures in short (2 h) exposures. Rearing at 15 degrees C: (12L:12D), (a cold acclimation regime for F. occidentalis), does not protect against the sold shock induced by direct transfer to -11.5 degrees C (which rapid cold hardening does) but does extend survival time at -5 degrees C (i.e. increased chill tolerance) whilst rapid cold hardening does not. The rapid and longer term cold hardening responses in F. occidentalis therefore appear to have different underlying mechanisms. (C) 1997 Elsevier Science Ltd.