A “war” between insects to save the chestnut trees

In the last few days, technicians of  Lombardy Region (General Agriculture Department, led by Marco Boriani and Marilisa Molinari), have released the parasitoid insect Torymus sinensis into the woods of Arsago Seprio, in the Ticino Park. This insect is the natural rival of the chestnut gall wasp (Dryocosmus kuriphilus), which has been causing serious damage to the chestnut trees in our area, for some years.

Those present at the release included representatives of the Association Amici della Bozza di Rugn, Mayor Montagnoli, and Alberto Senaldi from the Direction of Slow Food for Varese Province, the person responsible for the territory, projects and culture.

The operation is part of Lombardy Region’s plan to fight the chestnut gall wasp throughout the region; this year, they have directed their interventions also at Arsago Seprio (Ticino Park), because of the effective concern of the local community, who have always been attentive to conservation of the woodland and environment.

On the same day, Dr Boriani carried out a series of releases of Torymus sinensis into the woods of Somma Lombardo, in the Vignazze area (accompanied by the photographer, Aldo Genoni), and later in Lentate, near Sesto Calende, and Corgeno, near Vergiate, which are all in the Ticino Park.

The introduction of Torymus Sinensis into Varese Province, which was also done three years ago in Valcuvia and in the Campo dei Fiori Park, is an important step in controlling the damage caused by the oriental chestnut gall wasp. With its spread and the formation of the classic galls, it seriously compromises the development of leaves and buds, reducing the photosynthesising surface and preventing the production of nuts. The weakening of these trees leads to the onset of other diseases, which are often lethal, such as cancer and other diseases of the root system.

After the release of the parasitoid, the female Torymus Sinensis lay its eggs in the galls of the wasp, whose larvae will later be “parasitised” by those of the Torymus, leading to their death. In some parts of Piedmont, where releasing this insect began in 2006, galls have diminished, and the percentage of “parasitised” galls already exceed 80-90%, with a substantial and visible benefit for the chestnut trees.

Recent monitoring operations in most of Lombardy confirm that the insect has spread well, and the hope is that, within a couple of years, the biological control of the wasp will give comforting results also in our area, and that the chestnut trees will resume their normal appearance.

In this way, the trees will bloom better and produce nectar for the bees, and, in autumn, we will be able to gather chestnuts, which were an important resource for local people, in the woods, as we once did.