Introduction to the symposium on search and detection

[First paragraph...]
Those managing biosecurity at borders or eradicating weeds, pests and diseases share a common problem. Unless the unwanted organism is highly conspicuous, it can be extremely difficult to find the first few invaders, or the last few survivors. Thus, non- detection after a search does not necessarily mean the animal, plant or disease is not in fact present. Depending on the effectiveness of the search, the absence of evidence may provide only weak evidence of absence. These uncertainties create risks for managers. Falsely declaring an unwanted organism absent when it is in fact present but undetected is likely to have adverse, and potentially major, biological, economic and political consequences. Conversely, it is obviously wasteful to continue with management and surveillance when in truth the organism is no longer present.