Candidate weed biocontrol agents must be screened to exclude those that could threaten desirable plants . Traditionally , this has been done by rejecting species that develop on economically important plants in laboratory no - choice tests . However , because congeneric plants often support development in these tests , even when they are not utilized in nature , the tests do not meet legislated requirements for rare plant species or the increasing public concern for native plants . Plant suitability for larval development is a poor predictor of host range because insects use a sequence of steps in which the early steps , such as host finding and acceptance for oviposition , tend to be stronger than the later ones , such as suitability for development . This study is a trial of a new approach to screening insects as weed biocontrol agents that uses risk analysis to quantify the suitability of a plant as a host on the basis of inset performance at various stages in its life cycle . The insects used for the study was a NW Chinese biotype of the leaf beetle , Altica carduorum, which in terms of climate adaptation and damage it inflicts on the weedy thistle Cirsium arvense, is a promising biocontrol agent for Canada . However , its ability to develop on all North American Cirsium spp . in laboratory no - choice tests currently excludes its release . We show by risk and factor analyses , with five sequential host - selection parameters , that the suitability of these thistles to A. carduorum is so low that the beetle would not jeopardize the continued existence of rare native thistles , so its release should not be a problem .