The citrus longhorned beetle (Anoplophora chinensis) is native to Asia where it is widespread. Currently established in Italy, Croatia and Turkey, this insect has entered new areas mainly through the trade in ornamental plants, especially bonsai. In 2018, an outbreak was detected in the municipality of Royan, where eradication measures are being implemented. ANSES conducted an expert appraisal to assess the risk of spread and the measures to be considered to eradicate the outbreak.
A threat to many different trees
This insect is large, measuring 25 to 35 mm, with antennae at least as long as its body. It is capable of attacking more than 20 different botanical plant families, including maple, hazel, birch, hornbeam, plane, cherry laurel, chestnut, etc.
The damage it causes in trees is mainly due to the development of its larvae, which are difficult to detect. As they feed, they tunnel into the branches and trunk just under the bark, then penetrate the woody tissues of the lower part of the trunk and roots. If uncontrolled, the insect can kill infested trees within just a few years.
This pest has great longevity and a flight capacity that enables it to spread over a distance of several kilometres. It can also exhibit "hitchhiker" behaviour, meaning that it can be introduced via transported plants, in particular. To date, no natural enemies have been identified to combat this pest.
Analysis of management measures
European regulations require the clear-cutting of all plants susceptible to this pest, along with their roots, within a radius of 100 metres around infested plants. However, they stipulate that exceptions to felling may be noted and replaced by a detailed examination of all such plants within this radius for signs of infestation.
For the outbreak in question, felling in the 100-metre area around officially infested plants was planned for between November 2018 and March 2019, i.e. outside the insect's flying period.
Any prioritisation of felling and stump removal to manage the large number of plants, trees and shrubs identified to date would require the extension of the outbreak – currently strongly suspected – to be taken into account.
Following the risk assessment, the experts concluded that any exceptions for the felling of host plants in the 100-metre area would increase the risk of citrus longhorned beetle spreading in Royan and outside the municipality.
Recommendations for eradicating the Royan outbreak
Since chemical and biological control measures are inadequate in terms of their safety and effectiveness, only physical control based on felling and destruction of susceptible plants can be considered. Furthermore, the use of protective netting is not an effective substitute.
In addition to felling all host plants within a radius of 100 metres, the experts reiterated the importance of implementing the surveillance plan over the whole 2 km area around the outbreak, especially while the exact point of entry is unknown. Plant inspections may be supported by searches employing a canine unit twice a year, in early spring and autumn.
Lastly, the participation of local inhabitants is vital to ensure that cases of infestation on trees are rapidly detected. A specific plan to inform the public about the management plan in place is therefore essential, to explain the risks and damage, the symptoms associated with the pest, and the services to be contacted in the event of detection.