That is the question which has been raised after ragweed leaf beetles greatly reduced the weed in neighbouring Italy. Ragweed – ambroisie in French – was introduced to France in cargo from the US in 1863. It has since established itself, especially in the river valleys of the south east but also along the Dordogne and in other parts of the south west.
Introducing, the ragweed leaf beetle
Around 10% of people have allergic reactions to its pollen in the late summer, some so badly that they cannot go outside. Italian researchers noted that a fall in ragweed pollen was associated with the arrival in the country of a brown bug called Ophraella communa, also known as ragweed leaf beetle.
Bruno Chauvel, a researcher at environmental research body Inrae in Dijon, said: “The fall was so marked that they waited three years before publishing the results, to check that there were not other environmental factors at play. Then they published astounding figures of how the little beast lays its eggs on the plant and then, when they hatch, they eat all its leaves and moves on to the next one.”
There have been campaigns in France to attack the weed using weedkiller, mechanical hoes, and manual methods such as strimmers, but they have not been successful. In spite of the effect Ophraella communa has had in Italy, there is hesitation about deliberately introducing it here, said Dr Chauvel.
Hesitations and considerations
“The main problem is that ragweed is closely related to sunflowers and there are fears that after eating ragweed, the insects might then turn to sunflowers, which are an important crop in the south of France. No one wants sunflower farmers to have to start using more insecticides.” Philippe de Goustine, president of the Stop Ambroisie association, said: “The health authorities in France did a study which said the risk of introducing the insect was low, but they still did not give their go-ahead. There is no chance that it will be introduced this year, and very little that things will change in 2021.”
He added that new research showing the insect had suddenly disappeared from around Milan, possibly because of a cold spell, showed the difficulty of bio-control methods. “We have a plan in France for local communes to each have someone appointed to head the fight against this plant which makes so many people sick,” he said. "We need people on the ground, who know their local areas, to co-ordinate the fight, adapting the method to each spot. People should get involved now, or in 20 years’ time the plant will be everywhere and there will be a real national health crisis.”