Torymus sinensis, a tiny parasitic wasp originally from China, has been used in French chestnut orchards since 2011 to control an invasive pest. Researchers from INRAE, a French agricultural research organization, have not been able to breed the wasp in the laboratory, so they collect samples of galls—abnormal growths on plants caused by the pest—and wait for the wasps to emerge naturally. In 2013, 300,000 galls were stored in Sophia Antipolis, a research hub in the south of France, to support the program. The pest being targeted, the chestnut gall wasp (Dryocosmus kuriphilus), is a small black insect less than 3 mm long that originated in China. It first appeared in Italy in 2002 and was detected in France in 2007 in the Alpes-Maritimes region, likely through contaminated plant material. By 2010, it had established itself in Ardèche, a major chestnut-producing area that accounts for about 44% of the country’s chestnut output. The wasp reproduces through parthenogenesis, meaning only females exist, and each can lay up to 100 eggs in the buds of chestnut trees. These eggs cause galls that can grow up to 25 mm in size. The damage is often not visible in the first winter, making the infestation hard to detect and allowing it to spread rapidly. Infestations have had a severe impact on chestnut production. In Corsica, production dropped from 637 tonnes in 2012 to 150 tonnes in 2014—a decrease of 76%. The AOP chestnut flour from Corsica also declined, from 110 tonnes in 2010 to 16 tonnes in 2018, losing about 85% of its volume. Chestnut honey, which makes up about 22% of French honey production, has also been affected. Traditional chemical treatments were not effective in mountainous regions, and mechanical control was only feasible for small infestations. Only one resistant chestnut variety, Bouche de Bétizac, developed in 1962 by INRA, has been mentioned as a possible solution. Torymus sinensis was discovered in China in 1975 and tested in Japan in the late 1970s. The wasp lays its eggs in the galls created by the chestnut gall wasp, and its larvae feed on the pest’s eggs, effectively controlling the population. Starting in 2011, INRAE released about 900 wasps in eight locations across France, including Ardèche, Corsica, and Drôme. The number of releases increased significantly over the following years, reaching about 70,000 parasitoids by 2014. The wasps are typically released in tubes containing 50 females and 25 males, opened in mid-April. Between 2011 and 2014, the number of released insects increased by nearly 80 times. These efforts were coordinated by a steering committee involving INRAE and local stakeholders. The program was tested from 2011 to 2015 before being widely deployed. Since then, the wasp has been found on all release sites, and INRAE reports a “complete success” in controlling the pest. The recovery of chestnut production has been faster in some areas, with the first sites in the Southwest returning to pre-infestation levels by 2017. However, in other regions like Corsica, production has not yet returned to its 2012 levels. INRAE continues to monitor the long-term effectiveness of the program, more than a decade after the initial releases.