All insect species and plant pathogens found attacking a weed in its native range are potential biological control agents. But before the potential of any one species can be realised, living specimens must be shipped; often more than half way around the world; extensively tested for host specificity; successfully reared and eventually, if all obstacles are overcome; mass reared and field released in the new country (See Weed Biocontrol: The Steps). It takes CSIRO from one to six years to process a single insect species (Cullen 1992). Given this enormous investment in research time and resources, potential control agents should be prioritised so that resources can be directed to those agents with the greatest potential for successful biological control.

It follows that the longer the list of potential agents and the smaller the budget the more critical the prioritisation process, because species given even a medium priority rating on a long list may never be tested and released. And if some of the species given a high priority are technically difficult to test, rear or culture (e.g. Marohasy 1993), the number of potential agents processed is likely to be further reduced because of time and resource constraints. Obviously budgetary and technical considerations are important when prioritising potential agents and should be given formal consideration (Beirne 1985).

Jennifer Marohasy