No loss of genetic divergence in Torymus sinensis following its release for Dryocosmus kuriphilus control in Europe

Arrival, establishment, and further dispersal of non-native natural enemies are considered essential for a successful biological control programme, while among the factors that may determine the success of such a programme, genetic diversity of the introduced population plays an important role in the establishment of a non-native species.The Chinese parasitoid wasp Torymus sinensis Kamijo (Hymenoptera: Torymidae) was initially released in Europe in Italy to control biologically the Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), and reduce the damage induced on sweet chestnut (Castanea sativa Miller). In the following years, T. sinensis was then released in numerous other European countries as a biological control agent of D. kuriphilus. Its presence has also been reported beyond the countries of release due to rapid natural dispersal.To assess the post-release genetic diversity of D. kuriphilus, we screened T. sinensis populations from six European countries and tested the possibility of these populations suffering from frequently observed genetic effects that could threaten its successful establishment in Europe.Our results exhibit that T. sinensis populations have suffered neither from the Allee effect nor from genetic bottleneck after their release and establishment in Europe, something that increases the possibility to effectively control D. kuriphilus in Europe.

Automated summary

The arrival, establishment, and dispersal of non-native natural enemies are crucial for a successful biological control program. The genetic diversity of the introduced population also plays an important role in the establishment of non-native species. The Chinese parasitoid wasp Torymus sinensis has been released in Europe to control the Asian chestnut gall wasp and reduce damage to sweet chestnut trees. It has been found that the genetic diversity of T. sinensis populations in Europe has not been negatively affected, which increases the possibility of effectively controlling the Asian chestnut gall wasp.