Biocontrol without borders: the unintended spread of introduced weed biological control agents

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 Melaleuca quinquenervia in Florida, USA has resulted in the release and establishment of Oxyops vitiosa and Boreioglycaspis melaleucae. An international survey of M. quinquenervia populations in 13 other states or countries where the insects have not been intentionally introduced 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 within the canopies of several M. quinquenervia trees near San Juan, Puerto Rico. In 2007, O. vitiosa was observed on the island of New Providence in the Bahamas but neither herbivore was detected on nearby Grand Bahama or Andros islands. In 2009, B. melaleucae was observed attacking M. quinquenervia trees in Los Angeles, California (USA). The herbivores have not been detected on other surveyed M. quinquenervia populations in Cuba, Jamaica, Texas (USA), Costa Rica, Brazil, Hawaii (USA) or South Africa.There is no evidence to suggest that herbivore colonization of New Providence, Puerto Rico, or California 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 from 200 to [3500 km from their original release location (Florida) and at locations that have strong links 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 of biological control agents.

An early suitability assessment of two exotic Ophraella species (Coleoptera: Chrysomelidae) for biological control of invasive ragweed in Europe

“…1B) (Pratt & Center, 2012), our results may also be used to alert authorities in the specifi ed areas to the potential future establishment of O. communa in their area. Based on our fi ndings, the French Agency for Food, Environmental and Occupational Health & Safety has already created an Expert Group to conduct a Pest Risk Analysis (Anses, 2015) and recently also a Benefi t Analysis for O. communa in France, where the species does not currently occur.…”

Measuring and evaluating ecological outcomes of biological control introductions

“…We also need to acknowledge that biological control organisms may spread far from their release sites (Petit et al, 2009;Pratt and Center, 2012). Any populationlevel damage that was not expected must be carefully investigated and may result in changes in assessment procedures.…”

The Stages of Invasion

“…Numerous examples of insects undergoing such range extensions have been reported amongst species introduced for weed control (as herbivores) or arthropod pest control (as predators or parasitoids), with a variety of undesirable non-target impacts (Parry 2009 ). Pratt and Center ( 2012 ) pondered whether any geographical barriers remain that can realistically restrict spread of introduced natural enemies, especially due to the increased impacts of globalisation and human-facilitated transport systems. Investigations on insects released as classical biological control agents suggest that release size, the number of potential propagules, may infl uence establishment -but trials with the European psyllid Arytainella spartiophylla released to control broom ( Cytisus scoparius ) in New Zealand found this to be important only for the fi rst year after psyllid release (Memmott et al 2005 ).…”