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United States Department of Agriculture

Agricultural Research Service

Title: The Role of Pre-Release Efficacy Assessment in Selecting Classical Biological Control Agents for Weeds - Applying the Anna Karenina Principle

item Mcclay, Alec - MCCLAY ECOSCIENCE
item Balciunas, Joseph

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 2005
Publication Date: December 1, 2005
Citation: Mcclay, A., Balciunas, J.K. 2005. The role of pre-release efficacy assessment in selecting classical biological control agents for weeds - applying the anna karenina principle. Biological Control. 35(3):197-207.

Interpretive Summary: Invasive weeds degrade natural areas, cause billions dollars worth of losses in agriculture, and attempts to control them account for more than half the pesticides used in the United States. Classical biological control B the release of carefully selected and tested insects and other natural enemies from the native home of the weed B is a proven strategy for reducing the impacts of invasive weeds, and reducing the use of herbicides. To avoid direct impacts on crops and beneficial native plants, prior to release, the intended agents are screened to assure that they are host-specific, and will not damage non-targets. However, even an agent that is restricted to its target, can cause indirect impacts to other organisms, especially if it becomes numerous, but fails to reduce the target weed's population. It is, therefore, prudent to assess, prior to release, the potential efficacy of a proposed agent. In this paper, we used project simulation models to compare the value of doing pre-release assessments. Our results suggest that unless the costs of pre-release efficacy testing greatly exceeds those for host specificity testing, they will be cost-effective in reducing release of ineffective agents. This should encourage other scientists to also conduct pre-release efficacy assessments of potential biocontrol agents, thereby reducing the risk of possible indirect effects.

Technical Abstract: When selecting classical biological control agents for weeds, the goals are to identify agents that will be both safe for release and effective in controlling their target plants. The introduction of ineffective agents should be avoided if possible, as such agents add to the costs and risks of biological control without contributing to its benefits. While the principles of host-specificity testing and risk assessment for weed biological control agents have been extensively debated and refined, there has been little attention in recent years to developing methods of assessing the probable efficacy of agents from pre-release studies. This reluctance to undertake pre-release efficacy assessment (PREA) is probably based on concerns that it will both add to the cost of screening biological control agents and introduce a risk of wrongly rejecting effective agents. We used a project simulation model to investigate the implications of using PREA as a filter in the agent selection process. The results suggest that, if it can be done at a lower cost than host-specificity testing, the use of PREA as the first filter can make agent selection more cost-effective than screening based on host-specificity alone. We discuss examples of PREA, and potential approaches. Impact of biocontrol agents is a function of their range, abundance, and per capita damage. While it will always be difficult to predict the post-release abundance of biological control agents from pre-release studies, some estimates of potential range can be obtained from studies of climatic adaptation. Experimental measurement of per-capita damage by agents to their target weeds is feasible and can contribute to a reduction in the numbers of ineffective agents released.

Last Modified: 4/19/2014
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