Cold tolerance, overwintering and establishment potential of Thrips palmi

The cold tolerance and overwintering survival of the quarantine regulated p est and virus vector, Thrips palmi (Karny) (Thysanoptera: Thripidae), is ex amined and discussed in terms of its establishment potential in the U.K. Th rips palmi adults and first-instar larvae have a wide distribution of super cooling points (SCPs) but show 'pre-freeze' mortality as a result of both a cute and chronic exposures to temperatures above the SCP range. Thrips palm i did not develop enhanced cold tolerance in response to cues previously sh own to cold-acclimate other thrips species. The acute cold tolerance of T. palmi is higher than that of the recently established and biologically simi lar species, Frankliniella occidentalis, which is thought to be capable onl y of very limited winter survival outdoors in the U.K. However, the more ec ologically meaningful chronic assays reveal the opposite pattern. If introd uced to the U.K., overwintering of T. palmi would thus be largely restricte d to protected environments, as its cold tolerance is insufficient to permi t outdoor survival for a complete winter. This assertion was demonstrated b y caged populations that died out after as little as 25 days in outdoor win ter conditions in Yorkshire, U.K. The reversal of relative tolerance of the two species when considering chronic and acute assays suggests that these forms of low temperature mortality have different physiological bases, and emphasizes the need to use both forms of assay in assessments of overwinter ing capacity.