Concerns are often raised about the introduction of non-native insects around the world to control weeds, citing the risk the introduced insects may cause to other desirable plant species. Yet a new international study suggests there may not be as much evidence for this concern as people perceive.
 
An international collaboration - including Max Suckling, Ph.D., of Plant & Food Research in Lincoln, New Zealand, and René Sforza, Ph.D., of the European Biological Control Laboratory in Montpellier, France, has completed a study on the effects of all recorded cases since the 1800s of insects as weed biological control agents, thanks to funding from an OECD Fellowship and as part of New Zealand’s government funded Better Border Biosecurity programme (http://plantandfood.us5.list-manage1.com/track/click?u=1b46d14e528ad30bae8b3663c&id=1bbcd681af&e=96a8f4840c).
 
The research characterised the magnitude of unwanted effects by these insects on other plants using a five-step scale adapted from invasive species biology and looked at 512 cases of deliberately introduced biocontrols dating back more than 150 years.
 
Suckling said “A total of 43 weed biocontrol insects worldwide have been reported to feed on non-target plants after release, but the real surprise comes when you look at the level of this feeding and what little effect it is having on the plants, compared with calls for concern about biosafety in the scientific literature”.
 
The study particularly looked at whether insect feeding affected the reproductive rate of the non-target plant and discovered decreases in plant reproduction in non-target plants to be very rare. The scientists found only four insects causing plant populations to decline significantly anywhere.
 
“Weeds are a major long-term drain to our quality of life. Our concern is that worry about biosafety needs to be tempered with the benefit scenario. Our analysis shows that as far as is known, weed biological control agents have historical had an excellent biosafety track record, with more than 99 percent of cases avoiding significant non-target impacts on plant populations” said Suckling.
 
“Biological control of weeds through the introduction of specific insects is an environmentally sustainable solution compared to chemical sprays and an area of science we aim to investigate further” noted Sforza, currently visiting New Zealand on an OECD Fellowship for biological control.
 
The study estimates that in the nearly 85-year history of weed biological control in New Zealand, 34 percent of insects deliberately introduced against weeds have worked successfully, in some cases with real benefits. Two key success stories have occurred from insects introduced to control St John’s Wort and Ragwort, with long-term ecosystem recovery over large areas.
 
The study notes that in the future it is expected that even fewer non-target impacts and greater benefits can be expected due to improved science and increased incorporation of wider societal values and that suitably-screened organisms can be released with a very high degree of specificity against weeds.
 
View the research paper online:
PLoS ONE – article by Suckling and Sforza,
What magnitude are observed non-target impacts from weed biocontrol? 
10.1371/journal.pone.0084847