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Biological Control of Insects and Weeds

Biological control was defined by DeBach (1964) as "the actions of parasites, predators, and pathogens in maintaining another organism's density at a lower average than would occur in their absence." Nordlund (1996) reviewed the different concepts of biocontrol as applied to weeds and insects, and in particular the different "conceptual models" of biocontrol. Within these definitions, there are 3 different techniques for applied biocontrol:

  1. Conservation - protection or maintenance of existing populations of biocontrol agents;
  2. Augmentation - regular action to increase populations of biocontrol agents, either by periodic releases or by environmental manipulation; and
  3. Classical biocontrol - the importation and release of exotic biocontrol agents, with the expectation that the agents will become established and further releases will not be necessary.

Most of Integrated Pest Management (IPM) is about the first two methods; conservation of natural biocontrol agents and augmentation through regular releases. This page is chiefly about the third method, classical biocontrol. Unlike the other methods, classical biocontrol is permanent; that is, once successful control of a pest is achieved, the control will continue indefinitely unless disrupted by the introduction of hyper-parasites. It is therefore much cheaper than other methods in the long run. It does not require action by the farmers and so adoption in the field is not a problem. However, because it is permanent it is important that all possible consequences are considered beforehand. Because agents spread unaided, conflicts of interest must be resolved before any release is made. Because agents spread across property boundaries, the pest will be controlled whether the farmers pay for the agent or not, therefore commercial companies cannot sell the agents.

For more details about agent imports, visit the AQIS WWW site (http://www.dpie.gov.au/aqis/homepage/aqishome.html.)