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United States Department of Agriculture

Agricultural Research Service


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Title: What magnitude are observed non-target impacts from weed biocontrol?)

item Sforza, Rene
item Suckling, D

Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/19/2013
Publication Date: 1/13/2014
Citation: Sforza, R., Suckling, D.M. 2014. What magnitude are observed non-target impacts from weed biocontrol?. PLoS One. 9(1): e84847. doi:10.1371/journal.pone.0084847.

Interpretive Summary: The increasing incidence and impact of invasive species is widely recognised as a major and increasing threat to food and fiber production, as well as ecosystem functioning, so it can be assumed that the need for classical biological control to mitigate costs is increasing. We reviewed all case studies from 150 years of biocontrol of weeds worldwide with a special emphasis on non-target effects. We limited our consideration to adverse non-target impacts, which should logically take into account the impacts on individual plant taxa (native and valued plants), irrespective of how many biocontrol agents have been involved. We reviewed the reported non-target impacts by magnitude of impact on plant species on a five-step scale (minimal, minor, moderate, major, massive). Our analysis showed that weed biological control has a historical biosafety track record of >99%, and fewer non-target impacts can be expected in future because of improved science and incorporation of societal values. Our approach offers the benefit of providing to weed scientists and practitioners a standardised framework for observing change in impact over time, since a number of effects are likely to be in flux, for example due to expanding geographic range.

Technical Abstract: A systematic review focused by plant on non-target impacts from agents deliberately introduced for the biological control of weeds found significant non-target impacts to be rare. The magnitude of direct impact of 43 biocontrol agents on 140 non-target plants was retrospectively categorized using a risk management framework for ecological impacts of invasive species (minimal, minor, moderate, major, massive). The vast majority of agents introduced for classical biological control of weeds (99% of 512 agents released) have had no known significant adverse effects on non-target plants thus far; major effects suppressing non-target plant populations could be expected to be detectable. Most direct non-target impacts on plants (91.6%) were categorized as minimal or minor in magnitude with no known adverse long-term impact on non-target plant populations, but a few cacti and thistles are affected at moderate (n = 3), major (n = 7) to massive (n = 1) scale. The largest direct impacts are from two agents (Cactoblastis cactorum on native cacti and Rhinocyllus conicus on native thistles), but these introductions would not be permitted today as more balanced attitudes exist to plant biodiversity, driven by both society and the scientific community. Our analysis shows (as far as is known), weed biological control agents have a biosafety track record of .99% of cases avoiding significant non-target impacts on plant populations. Some impacts could have been overlooked, but this seems unlikely to change the basic distribution of very limited adverse effects. Fewer non- target impacts can be expected in future because of improved science and incorporation of wider values. Failure to use biological control represents a significant opportunity cost from the certainty of ongoing adverse impacts from invasive weeds. It is recommended that a simple five-step scale be used to better communicate the risk of consequences from both action (classical biological control) and no action (ongoing impacts from invasive weeds).

Last Modified: 8/24/2016
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