Effects of Temperature on the Establishment of Non-native Biocontrol Agents: the Predictive Power of Laboratory Data

The European Union (EU) and its constituent governments are committed to increasing the success of biocontrol in Europe, and are currently seeking a pan-European balanced regulatory system to aid this objective. The concept of ‘balance’ recognizes that (a) the complexity of any licensing system must be proportionate to risk, (b) industrial producers of biocontrol agents have limited RandD budgets, but (c) there can be no compromise on environmental safety. Whilst there is common agreement between agencies responsible for environmental protection, regulators and industrial producers, about the ecological information required to assess the establishment potential of non-native species, the research methods by which such data can be generated (if not available in the literature), have not been fully developed or tested. The inappropriate use of ‘climate matching’ between native and introduced ranges as a ‘proxy’ for cold tolerance and overwintering ability is one example of this problem. Most predatory insects and mites used in glasshouse biocontrol in the UK originate from tropical and semi-tropical climates. For this reason, the licensing system for the introduction of non-native species has operated under the assumption that winter would act as a natural barrier to the establishment of such species outside of glasshouse environments. This view has been challenged by the establishment in the wild of the predatory mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) and the discovery of the predatory mirid Macrolophus caliginosus Wagner (Hemiptera: Miridae) outside of glasshouses in winter. Whilst the impact of these species on native ecosystems is unknown, their establishment is considered undesirable. This paper describes a series of experiments used to determine a range of thermal characteristics (developmental threshold, day-degree requirement per generation, supercooling point, lethal times and temperatures, field survival) of five non-native biocontrol agents. A strong correlative relationship was found between the time at which 50% of populations die in the laboratory at 5°C (LTime50) and duration of winter survival in the field. The comparative data provide a retrospective ecophysiological explanation for the establishment of N. californicus and occurrence of M. caliginosus outside of glasshouses, and also indicate that Delphastus catalinae (Gordon) (Coleoptera: Coccinellidae), Eretmocerus eremicus (Rose and Zolnerowich) (Hymenoptera: Aphelinidae) and Typhlodromips montdorensis (Schicha) (Acari: Phytoseiidae) would not survive outdoors in the UK under current climatic condi-