Biological Control 35 (2005) 55–67 www.elsevier.com/locate/ybcon 1049-9644/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2005.06.008 Does fundamental host range match ecological host range? A retrospective case study of a Lygus plant bug parasitoid T. Haye a , H. Goulet b , P.G. Mason b , U. Kuhlmann a,¤ a CABI Bioscience Centre, Agricultural Pest Research, Rue des Grillons 1, CH-2800 Delémont, Switzerland b Agriculture and Agri-Food Canada, Research Centre, K.W. Neatby Building, Ottawa, Ont., Canada K1A 0C6 Received 15 March 2005; accepted 21 June 2005 Available online 10 August 2005 Abstract Using the retrospective case study of Peristenus digoneutis (Hymenoptera: Braconidae) introduced in the United States for bio- logical control of native Lygus plant bugs (Hemiptera: Miridae), laboratory and Weld studies were conducted in the area of origin to evaluate whether the fundamental host range of P. digoneutis matches its ecological host range. Furthermore, it was determined whether these approaches would have been indicative of the post-introduction host range of P. digoneutis in North America [Day, W.H., 1999. Host preference of introduced and native parasites (Hymenoptera: Braconidae) of phytophagous plant bugs (Hemip- tera: Miridae) in alfalfa-grass Welds in the north-eastern USA, BioControl 44, 249–261.]. Seven non-target mirid species were selected to deWne the fundamental host range of P. digoneutis in the area of origin in Europe. Laboratory choice and no-choice tests demon- strated that all selected non-target species were attacked by P. digoneutis and were largely suitable for parasitoid development. To conWrm the validity of the fundamental host range, the ecological host range of P. digoneutis in the area of origin was investigated. Peristenus digoneutis was reared from 10 hosts, including three Lygus species and seven non-target hosts from the subfamily Mirinae. Despite the fact that laboratory tests demonstrated a high parasitism level in non-targets, ecological assessments in both North America (Day, 1999) and Europe suggest a much lower impact of P. digoneutis on non-target mirids, with low levels of parasitism (below 1% in Europe). Therefore, ecological host range studies in the area of origin provide useful supplementary data for interpret- ing pre-release laboratory host range testing.  2005 Elsevier Inc. All rights reserved. Keywords: Biological control; Fundamental host range; Ecological host range; Non-target eVects; Risk assessment; Lygus plant bugs; Parasitoids; Braconidae; Peristenus digoneutis 1. Introduction Within the last twenty years, concerns regarding the safety of arthropod biological control using invertebrates have increasingly been discussed (e.g., Howarth, 1983, 1991; SimberloV and Stiling, 1996; Follett et al., 2000; Lynch et al., 2001; Stiling, 2004). It has been stressed that classical biological control could have major environmen- tal costs if introduced natural enemies colonize and disrupt native systems ( Hawkins and Marino, 1997). The main areas of concern include the irreversibility of exotic intro- ductions, the dispersal of non-indigenous natural enemies to new habitats, and the potential host range expansion of the agent to include native or bene Wcial insects, thereby causing harm to such non-target hosts (non-target eVects), (e.g., Howarth, 1983, 1991; Secord and Kareiva, 1996; Sim- berloV and Stiling, 1996; Follett et al., 2000; Lockwood, 2000; Michaud, 2002; Kuris, 2003; Louda et al., 2003a; Stil- ing, 2004). However, despite the relatively large number of exotic natural enemies introduced for biological control of insects and mites (Greathead, 1995; Wratten and Gurr, 2000), negative environmental eVects from such releases * Corresponding author. Fax: +41 32 421 4871. E-mail address: u.kuhlmann@cabi.org (U. Kuhlmann).