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Researchers detail the migrations of the wood wasp <i>Sirex noctilio</i>

The <i>Sirex noctilio</i> wood wasp is one of the great enemies of the trees in the <i>Pinus</i> family. It originated in Eurasia and from there has spread since the beginning of the 20th century to Australia, South America and South Africa. To control its spread, it is essential to know the routes this insect has followed to carry out its colonisation.

In order to find out about its migrations, various research centres in South Africa, Sweden, Canada, Chile, Australia, Spain, Argentina and Switzerland have conducted research detailing its routes and expansion periods. A significant new fact has emerged and it is that the wasps returning to Europe from Chile and South Africa have undergone a genetic micro-evolution which makes them more resistant to their natural European enemy, a nematode that sterilises them. The Sirex noctilio wasp is regarded as a secondary pest in Europe because in this geographical area there is a natural enemy preventing its spread on a large scale. It is a nematode that gets into the wasp’s genital organs and sterilizes it. However, the wasp is a pest of great importance in the zones it has migrated to like Australia, South America and South Africa, where it does not have to contend with this natural enemy. In the countries where it has been accidentally introduced, the insect can even kill a tree, because when the females lay their eggs inside the trunk, they also release a fungus and a toxic mucoid substance which kills off the specimen. As an example of its devastating effect, one can cite that in Australia it succeeded in killing 40% of the pine trees after it was introduced halfway through the last century. The researchers want to make it quite clear that in Europe one must remain vigilant in the management of the Sirex noctilio. In the genetic analyses carried out, it has been discovered that samples originating in Chile and South Africa and which have been detected in Switzerland have undergone a genetic micro-evolution. This genetic modification makes them more resistant to the nematode that can render them sterile; so their capacity to reproduce and spread increases considerably. The specimens displaying this microevolution have an unknown genetic origin, even though specialists believe that they may have originated in Asia or North Africa. By combining molecular studies, experts have managed to establish the migratory routes of this species. According to their conclusions, the first presence of the wasp outside its native habitat was recorded in New Zealand in 1900, and the next one was recorded in Australia in 1961. Its advance continued from Europe and Oceania towards South America, where it settled in Uruguay in 1980, Argentina in 1985, and Chile in 2001. From the Southern Cone and Oceania, the wasp reached South Africa in 1994. The next migration took place from Europe and South America towards the United States and Canada where it settled in 2004 and 2005, respectively. To conduct this research, the researchers have genetically studied 500 specimens of the Sirex noctilio. The specimens captured on the Iberian Peninsula were analysed by the Basque Institute for Agricultural Research and Development, Neiker-Tecnalia. The research was led by E. Boissim, member of the Forestry and Agricultural Biotechnology Institute of the University of Pretoria (South Africa), and has had the participation of the following people: M. J. Wingfield, B. Slippers and B. Hurley, of the University of Pretoria (South Africa); R. Vasaitis and J . Stenlid, of the Swedish University of Agricultural Sciences; C. Davis and P. De Groots, of the Canadian Forest Service, Ontario (Canada); R. Ahumada, of Bioforest S. A., Concepción (Chile); A. Carnegie, of the Forest Science Centre, Beecroft (Australia); A. Goldarazena, of the Basque Institute for Agricultural Research and Development Neiker-Tecnalia, Vitoria-Gasteiz (Basque Country, Spain); P. Klasmer, of the Insect Ecology Laboratory, Bariloche (Argentina); and B. Wermelinger, of the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf (Switzerland).