Abstract
Classical biological control is an important means of managing the increasing threat of invasive plants. It constitutes the introduction of natural enemies from the native range of the target plant into the invaded area. This method may be the only cost-effective solution to control the rapidly expanding common ragweed, Ambrosia artemisiifolia, in non-crop habitats in Europe. Therefore, candidate biocontrol agents urgently need to be assessed for their suitability for ragweed control in Europe. A previous literature review prioritized the host-specific leaf beetle Ophraella slobodkini as a candidate agent for ragweed control in Europe, whereas it rejected its oligophagous congener O. communa. Meanwhile, O. communa was accidentally introduced and became established south of the European Alps, and we show here that it is expanding its European range. We then present a short version of the traditional pre-release risk-benefit assessment for these two candidate agents to facilitate fast decision-making about further research efforts. We selected two complementary tests that can be conducted relatively rapidly and inform about essential risks and benefits. We conducted a comparative no-choice juvenile performance assay using leaves of ragweed and sunflower, the most important non-target plant, in Petri dishes in climatic conditions similar to that in the current European range of O. communa. This informs on the fundamental host range and potential for increasing abundance on these host plants. The results confirm that O. slobodkini does not survive on, and is hence unlikely to cause severe damage to sunflower, while O. communa can survive but develops more slowly on sunflower than on ragweed. In parallel, our species distribution models predict no suitable area for the establishment of O. slobodkini in Europe, while O. communa is likely to expand its current range to include a maximum of 18% of the European ragweed distribution. Based on this early assessment, the prioritization and further assessment of O. slobodkini seem unwarranted whereas the results urgently advocate further risk-benefit analysis of O. communa. Having revealed that most of the European area colonized by ragweed is unlikely to be suitable for these species of Ophraella we suggest the use of such relatively short and cheap preliminary assessment to prioritise other candidate agents or strains for these areas.
Highlights
Invasions by alien plant species are increasing in frequency and severity (Lambdon et al, 2008; Early et al, 2016)
Our species distribution models predict no suitable area for the establishment of O. slobodkini in Europe, while O. communa is likely to expand its current range to include a maximum of 18% of the European ragweed distribution
We present a short version of the traditional pre-release risk-benefit assessment to quickly evaluate if the candidate agents O. slobodkini and O. communa are worth being subjected to further in-depth risk-benefit assessments
Summary
Invasions by alien plant species are increasing in frequency and severity (Lambdon et al, 2008; Early et al, 2016). The deployment of classical biological control (BC) may be an important, and often the only, option for managing areas that are too large or too sensitive to be subjected to chemical or mechanical control (van Wilgen et al, 2013; Seastedt, 2015). The introduced antagonists should establish stable populations and provide sustainable control by suppressing the abundance of the target plant below economic or ecological thresholds, while being of limited ecological risk in the introduced area Classical weed BC is a permanent, environmentally friendly and cost-effective management tool (Culliney, 2005; van Wilgen et al, 2013; Suckling & Sforza, 2014). It has successfully been used on several continents in the last 150 years (Winston et al, 2014), but only very recently in Europe (Shaw et al, 2016)
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