Biological Control 35 (2005) 338–347 www.elsevier.com/locate/ybcon 1049-9644/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2005.02.002 Evaluating risks of biological control introductions: A probabilistic risk-assessment approach Mark G. Wright a,¤ , Michael P. HoVmann b , Thomas P. Kuhar c , JeVery Gardner b , Sylvie A. Pitcher b a Department of Plant and Environmental Protection Sciences, University of Hawai’i at Ma ¯noa, Honolulu, HI 96822, USA b Department of Entomology, Cornell University, Ithaca, NY 14853, USA c Department of Entomology, Virginia Polytechnic Institute and State University, Painter, VA 23420, USA Received 28 May 2004; accepted 4 February 2005 Available online 10 March 2005 Abstract We address the need to develop improved quantitative procedures for estimating potential non-target impacts of biological con- trol agents in this paper, and propose a probabilistic risk-assessment approach. This approach employs risk-assessment procedures commonly used in many disciplines. The procedure described here uses precision trees to estimate risk based on probabilities that biological control agents will demonstrate predictable behavior under speciWc conditions, based on their ecological characteristics. We use Trichogramma ostriniae, an egg parasitoid deployed augmentatively against Ostrina nubilalis in the US as case study to con- ceptually demonstrate the proposed procedure. We propose that this new approach has potential for widespread use in quantifying non-target risk of biological control introductions prior to introductions being made.  2005 Elsevier Inc. All rights reserved. Keywords: Biological control; Non-target impacts; Risk assessment; Probabilistic; Trichogramma ostriniae 1. Introduction Invasive species and the ecological and agricultural threats they pose are rapidly increasing with the global- ization of markets and increased movement of goods and people worldwide (Perrings et al., 2002). Concomi- tant with this challenge is the development and imple- mentation of appropriate political, regulatory, and technical strategies to minimize the introduction of exotic species and, should they occur, the appropriate response. The latter may include all components of an integrated pest management strategy including cultural, chemical, and biological tools, each of which comes with a set of risks. The challenge faced is to determine which option poses the least risk while maximizing potential beneWts, a determination that may involve ecological, economic, sociological, and political components. Bio- logical control of invasive species is an attractive and fre- quently used strategy for the management of invasive species, but also a strategy that has attracted consider- able criticism as a potential ecological risk, in terms of non-target impacts upon indigenous species (Louda et al., 2003a). We describe here an approach to assessing such potential risks from new introductions for biologi- cal control, using probabilistic risk-assessment methods (Bedford and Cooke, 2001). This method requires quan- tiWcation of key ecological traits of the candidate agent for introduction, and the use of “precision trees” to eval- uate levels of likely exposure and impact the candidate may cause to likely non-targets. The proposed procedure will provide a valuable conceptual model for eVective risk-assessment procedures in biological control. ¤ Corresponding author. Fax: +1 808 956 2428. E-mail address: markwrig@hawaii.edu (M.G. Wright).