RAPID COLD HARDENING IN THE WESTERN FLOWER THRIPS FRANKLINIELLA-OCCIDENTALIS

A rapid cold hardening process is reported in first instar larvae of F rankliniella occidentalis. When larvae are transferred directly from 2 0 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 i s rapidly lost (after 1h at 20 degrees C), Rapid cold hardening extend s 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. Th e rapid and longer term cold hardening responses in F. occidentalis th erefore appear to have different underlying mechanisms. (C) 1997 Elsev ier Science Ltd.