Technical Abstract: An underlying assumption of classical biological control implies that intentionally introduced natural enemies will remain within the boundaries that delineate the program’s area of implementation. A weed biological control program targeting M. quinquenervia in Florida USA has resulted in the release and establishment of Oxyops vitiosa and Boreioglycaspis melaleucae. An international survey of 12 other M. quinquenervia populations was initiated to monitor the long range dispersal of O. vitiosa and B. melaleucae beyond the herbivores’ intended geographic range (Florida). Surveys in 2006 resulted in the discovery of B. melaleucae near San Juan, Puerto Rico. In 2007 O. vitiosa was observed at 6 locations on the island of New Providence in the Bahamas but neither herbivore was detected on Grand Bahama or Andros islands. In 2009 B. melaleucae was also observed attacking M. quinquqnervia trees in Los Angeles, California (USA). The herbivores have not been detected in Cuba, Jamaica, Texas (USA), Costa Rica, Brazil, Hawaii or South Africa. There is no evidence to suggest that herbivore colonization was influenced by linear distance between Florida and the recipient M. quinquenervia stand. While the dispersal pathway(s) remains unknown, biological control agents were detected in areas that have strong links with south Florida via tourism and trade as indicated by the number of airline flights connecting south Florida with colonized tree populations. Implications of this unintended spread are discussed in relation to permeability of biogeographical barriers and risk assessment.