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neAbstract Biologically based control methods oVer many advantages for the control of invasive plant species; however, these methods are not without risks to native species. Thus, there is a need for more eVective and eYcient methods of risk analysis for biological control agents. We show how the process of ecological risk assessment established by the United States ’ Environmental Protection Agency may be adapted to improve assessment of the risks of proposed biological control agents. We discuss the risks posed by weed biolog-ical control agents, and present a simple individual-based model of herbivorous insect movement and oviposition on two species of host plant, a target invasive plant species and a non-target native species, in simulated landscapes. The model shows that risks of non-target impacts may be inXuenced by the details of the movement behavior of biological control agents in heterogeneous land-scapes. The speciWc details of insect movement that appear to be relevant are readily measured in Weld trials and the general modeling approach is readily adapted to real landscapes. Current biological control risk assessments typically emphasize eVects analysis at the expense of exposure analysis; the modeling approach presented here provides a simple and feasible way to incorporate exposure analyses. We conclude that models such as ours should be given serious consideration as part of a comprehensive strategy of risk assessment for proposed weed biological control agents