The Japanese beetle (Popillia japonica) has now spread and become established outside its native Japan, initially in the USA and then in Europe. It was first spotted in Italy in 2014, and then in Switzerland in 2017. ANSES conducted an expert appraisal to assess the probability of the insect's introduction, as well as its impacts, and to recommend management measures for its surveillance and control. "So far, it has not been detected in France, but there is no reason why it should not enter the country," explains Christine Tayeh, scientific coordinator in the Expert Assessment of Biological Risks Unit of ANSES's Plant Health Laboratory, which led this expert appraisal. "According to the results of our expert appraisal, there is nothing to stop it becoming established in France either: it is an insect that moves around easily, the temperature and precipitation conditions here are favourable, and it will have no difficulty finding sources of food because it can feed on many of the plant species found in France."
The arrival of the Japanese beetle is a real cause for concern: the adult beetle prefers to feed on leaves, while the larvae feed on the roots of host plants. More than 400 species of plants are concerned, of which more than a hundred are present in metropolitan France. These include plants grown for food such as plum, apple, grapevine, maize, soy, beans, asparagus, etc.; forest species such as Norway maple and poplar; and ornamental plants, for example roses and certain species found in lawns and turf. By consuming the leaves, the Japanese beetle reduces the leaf area, decreasing the plant's ability to photosynthesise and thus potentially its yield. The damage caused by the insect can also reduce the aesthetic value of ornamental plants.
It is impossible to prevent the beetle from entering France: it can either fly here as an adult (from late May to September) or hitch-hike a ride, i.e. it can be transported on any surface, not just the plants it feeds on. The strategy used is therefore to detect its presence at an early stage, mainly by using traps equipped with combination lures (with both sex pheromones and floral attractants). These traps should be placed in strategic locations, such as along France's border with countries where the insect is present and near key entry points, such as ports or airports, as well as near transport networks. Raising awareness among the main players, mainly professionals in the various sectors concerned, is also recommended.
It is essential to act as soon as the insect arrives in the country: "We think there is a chance of eradicating the Japanese beetle from the beginning of the invasion, provided that we deploy dynamic surveillance and control methods while the population is still small and isolated. This is how it was eradicated from Oregon and California," says Christine Tayeh.
If an individual is detected, the working group tasked with the expert appraisal recommends first defining the infested area. This should then be subject to reinforced surveillance and the combined use of several control measures, adapted according to availability and authorisations for use. These include mass trapping, the use of synthetic plant protection products and biocontrol. In addition, cropping practices, such as reducing irrigation during the egg-laying period or tilling the soil in the autumn, have also been shown to be effective in reducing damage by adults and larval survival. If such action is not taken as early as possible after the Japanese beetle has been detected, the experts believe that it could take a long time to prevent any further spread once it has become established in the country.