The demand to be sure that only safe organisms are released and the emphasis placed on cage studies in host specificity tests has, in the past, forced very conservative assessments of potential control agents. As a result, some insects have not been released because they showed interest in non host plants when confined in cages with that test plant. With improved understanding of plant/insect interactions and better methods to assess likely hosts, the number of rejected agents will decline. In addition, a greater tolerance is being given to the use of oligophagus species when the possible negative impact of releasing an agent is minor compared to the considerable impact caused by allowing the weed to grow without control (eg. McFadyen and Marohasy 1990). These changes should help increase the chances of gaining control of the target weed and increase the global rates of success.

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