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°C to −11.5°C for 2 h there is 78% mortality, whereas exposure to 0°C for 4 h prior to transfer to −11.5°C reduces mortality to 10%. The response can also be induced by exposure to 5°C for 4 h or by gradual cooling at rates between 0.1 and 0.5°C min−1. The acquired cold tolerance is transient and is rapidly lost (after 1 h at 20°C). Rapid cold hardening extends survival times at −11.5°C and depresses lethal temperatures in short (2 h) exposures. Rearing at 15°C (12L:12D), (a cold acclimation regime for F. occidentalis), does not protect against the cold shock induced by direct transfer to −11.5°C (which rapid cold hardening does) but does extend survival time at −5°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.