Two specimens were captured in traps on July 1 and 2 in the eastern cities of Mulhouse and Saint-Hippolyte, close to France's borders with Germany and Switzerland, they said.

The two beetles probably came to France aboard a truck, train or car, the Grand-Est regional authorities said, a phenomenon known as "hitch-hiking".

The insects, native to Japan, have been detected in Italy since 2014 and in Switzerland since 2017. Last year, a Japanese beetle infestation was discovered in Basel, Switzerland, a city close to the sites of the recent French finds.

Japanese beetles pose a threat to more than 400 species of plants, according to the French health security agency Anses, which had warned since 2022 that the beetle could make it into France.

The insects threaten plum trees, apple trees, vines, corn, soy, green beans and asparagus, among other cultivated plants, as well as trees and ornamental plants such as roses.

The Grand-Est prefecture said that it had ordered increased surveillance of insect traps, as well as visual checks, to make sure that no other Japanese beetles were present.

It also called on the public to report any sightings of the beetles.

The European Union in 2019 designated the Japanese beetle as one of 20 harmful organisms that it said member states should destroy to prevent their spreading which it said could cause billions of euros (dollars) of damage.