Abstract. This study investigated the effect of temperature on the development and winter survival of the predatory mirid Macrolophus caliginosus Wagner, recently introduced into the U.K. as a biocontrol agent for glasshouse whitefly Trialeurodes vaporariorum. The developmental threshold for M. caliginosus calculated by three methods was between 7.3 and 8.4 C, with a day-degree requirement per generation varying between 472 and 524 day-degrees. It was estimated that under outdoor conditions M. caliginosus could complete two generations per year in the U.K. All life stages of M. caliginosus had supercooling points around À20 C, with some pre-freeze mortality evident in both acute and chronic low temperature exposures. Acclimation increased survival of nymphal M. caliginosus from approximately 24±52 days when exposed to a constant 0 C. Provision of prey extended survival of nymphs in the laboratory at a constant 5 C from 39 to 64 days and in the field by c. 150 days. The results are discussed in the context of the occurrence and establishment of M. caliginosus in the U.K. and the need to develop a reliable risk assessment system for non-native species used in glasshouse biocontrol.

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A series of recent studies have investigated the development, cold tolerance and winter field survival of glasshouse biological control agents that are non-native to the UK: Neoseiulus californicus, Macrolophus caliginosus, Delphastus catalinae, Eretmocerus eremicus and Typhlodromips montdorensis. The combined data sets for these species have been analysed to identify laboratory indices of cold tolerance that correlate with the duration of survival under winter field conditions. A strong correlation was found between the laboratory LTime 50 at 5°C and maximum field survival time. Both N. californicus and M. caliginosus survived substantially longer in the laboratory and in the field than the other species. It is suggested that the LTime 50 at 5°C may provide a reliable 'first stage' screen of establishment potential for candidate non-native biological control agents in the UK.

Abstract. Eretmocerus eremicus is a parasitoid wasp that is not native to Britain. It is a biological control agent of glasshouse whitefly and has recently been released under licence in Britain for the first time. This study assessed the effect of low temperature on the outdoor establishment potential of E. eremicus in Britain. The developmental threshold calculated by three linear methods was between 6.1° and 11.6 °C, with a degree‐day requirement per generation between 256.3 and 366.8° day−1. The supercooling points of non‐acclimated and acclimated larvae were similar (approximately −25 °C). Non‐acclimated and acclimated larvae were subject to considerable pre‐freeze mortality, with lethal temperature (LTemp50) values of −16.3 and −21.3 °C, respectively. Lethal time experiments indicated a similar lack of cold tolerance with 50% mortality of both non‐acclimated and acclimated larvae after 7 days at −5 °C, 10 days at 0 °C and 13 days at 5 °C. Field trials showed that neither non‐acclimated nor acclimated larvae survived longer than 1 month when exposed to naturally fluctuating winter temperatures. These results suggest that releasing E. eremicus into British greenhouses would pose minimal risk because typical British winter temperatures would be an effective barrier against establishment in the wild.