Hughes, Gwennan Elen (2010)
Ph.D. thesis, University of Birmingham.
\(Nesidiocoris\) \(tenuis\) Reuter (Hemiptera: Miridae) and \(Lysiphlebus\) \(testaceipes\) (Cresson) (Hymenoptera: Braconidae, Aphidiinae) are candidate biological control agents known to play an important role in the management of agricultural and horticultural pests in southern Europe. Through a series of laboratory and field assessments, this study investigates the establishment potential of these two species in cool temperate climates typical of northern Europe. Laboratory results demonstrated a low level of cold tolerance in \(N.\) \(tenuis\) with a developmental threshold of 12.9°C and no indication of ability to diapause. Field trials supported these findings with 100% mortality occurring after less than 4 weeks of winter field exposure. Collectively, these data suggest that \(N.\) \(tenuis\) is unlikely to establish outdoors in northern Europe and would therefore have little or no non-target effects on native species in such regions, thereby constituting a ‘safe’ candidate for release. Additionally, investigations into temperature-related thresholds indicated that \(N.\)\(tenuis\) would be an effective control agent against species with a similar activity profile to the two-spotted spider mite \(Tetranychus\) \(urticae\) Koch (Acari: Tetranychidae). \(Lysiphlebus\) \(testaceipes\)demonstrated a greater ability to tolerate cold than \(N.\) \(tenuis\) but there was no indication of ability to diapause. With a developmental threshold of 5.8°C, parasitoid larvae and pupae continued to develop during the 70 d of winter field trials yielding reproductively viable adults. With this level of cold tolerance and a host range in excess of 100 aphid species, including some known to overwinter in the UK and other temperate regions, it seems reasonable to predict that \(L.\) \(testaceipes\) would be able to establish in northern Europe. Thermal activity threshold investigations also indicated that \(L.\) \(testaceipes\) would constitute an effective control agent for pest species with similar activity profiles to \(Aphis\) \(fabae\) Scop. (Hemiptera: Aphididae) under a range of climatic conditions. These data are discussed in relation to current debate on the environmental risk assessment and regulatory system in Europe for the release of non-native biological control agents.
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