A Review on Applying Chalcid Wasps for Biocontrol of Dryocosmus kuriphilus

The chestnut gall wasp, Dryocosmus kuriphilus, a thelytokous cynipid, is one of the most serious pests of chestnut trees. Natural enemies, especially species of Torymidae, are considered as efficient biological control agents. In this article two similar parasitoids of D. kuriphilus, Torymus (Syntomaspis) beneficus and Torymus (Syntomaspis) sinensis (Hymenoptera: Torymidae), and the hybridization between them are described briefly. In addition, a delayed increase in the population of T. sinensis is also discovered. According to current study, two factors might play important roles: the low female sex ratio during several years after their releasing, and high mortality associated with the active facultative hyperparasism.