The red palm weevil: combating the loss of palm trees on the Mediterranean coast
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News of 19/12/2018
The palm weevil is one of the most damaging insect pests of palm trees, and is a threat to plant biodiversity in many countries. This insect has spread rapidly along the Mediterranean coast in the last ten years or more, and is classified as a regulated quarantine pest and a major danger to plant health in France. It is therefore subject to compulsory control measures. In order to curb the spread of the pest, which was introduced into the country in 2006, control strategies are being implemented at local and international levels. This context led ANSES to conduct an expert appraisal to identify better strategies to control the red palm weevil, particularly in the French Mediterranean area where palm trees are in danger of disappearing.
The palm weevil (Rhynchophorus ferrugineus)threatens most species of palm trees by destroying them from the inside, leading to dieback and collapse of the crown. It is particularly present on the coastline of the Provence-Alpes-Côte d'Azur region (French Riviera), but is also sporadically found in other French regions. As part of efforts to combat the palm weevil, the Ministry of Agriculture made a formal request to ANSES to identify the most appropriate control strategies according to the level of infestation by this pest.
Two situations identified in France in the fight against the red palm weevil
The ANSES experts drew on the conclusions of the 2017 report of the Food and Agriculture Organisation of the United Nations that "the needs to control the pest are directly correlated with the evolution of the red palm weevil populations".Based on this observation, the Agency defined two different situations for controlling this pest in France. Firstly, in the "Central-Atlantic" area, weevil eradication is possible through the use of preventive plant health measures such as regulatory action combined with surveillance and monitoring of palm trees, as well as mechanical sanitation and chemical or biological protection methods. And secondly, the situation in the "Mediterranean" area, where eradication of the weevil is virtually impossible. Here the objective is to stabilise the weevil's spread in order to reduce its impact on palm tree mortality.
To do this, the experts identified the most appropriate control strategies, incorporating curative and preventive approaches, on the basis of an assessment of the different control methods available, such as mechanical sanitation, application of insecticides, including biocontrol products authorised for this purpose such as products containing micro-organisms, application of entomopathogenic nematodes, and mass trapping of the pest.
Two proposed scenarios for preventing the spread of weevils in the Mediterranean region
By assessing the most effective operational methods while taking into account the cost of their implementation and their possible impact on the environment, several methods were identified in particular. In terms of methods that are harmless to the environment, a combination of two biocontrol products (Beauveria and Steinernema), applied strictly in accordance with the conditions of authorisation of the products concerned for this use, combined with mass trapping, was found to be the most appropriate method. It also appears that the injection of emamectin benzoate, administered strictly in accordance with the conditions of authorisation of the products concerned for this use, and whether or not combined with mass trapping, would be the least costly method. Moreover, the "Attract-and-Kill" trapping method, although not yet fully operational in the field, appears to be a potentially useful measure. On this basis, ANSES is proposing two different possible scenarios for controlling the palm weevil in the Mediterranean area:
- stabilise the red palm weevil population and limit its geographical range through appropriate control measures;
- give priority to protecting palm trees of heritage significance in infested areas and propose alternative plant species for unprotected areas.