Diversity and surge in abundance of native parasitoid communities prior to the onset of Torymus sinensis on the Asian chestnut gall wasp (Dryocosmus kuriphilus) in Slovenia, Croatia and Hungary

Abstract

Since the rapid spread of the Asian chestnut gall wasp (ACGW) throughout south-east Europe in the last few years, the possibilities of its control have been increasingly investigated. Due to constraints in available suppression measures in forest stands, biological control is recognized as the most suitable action to lower the abundance of the new invasive pest. Torymus sinensis, as a specialized parasitoid chalcid wasp of ACGW, was introduced to suppress the pest in Italy in 2005, and later in Croatia, Hungary (2014) and Slovenia (2015). We investigated the native parasitoid complex associated with ACGW in Slovenia, Croatia and Hungary over 8 years of sampling. We found 41 species of native parasitoids, eight of which are the first records on ACGW in Europe, adding up to a total of 51 species known to parasitize ACGW. These findings represent a large complex of cynipid-parasitoid fauna. Moreover, the abundance of native parasitoid populations on ACGW have demonstrated a temporal surge between the invasion of a new alien host (ACGW) and the onset of its specialized parasitoid, T. sinensis. Our results indicate that the introduced parasitoid acts as a very successful biocontrol of ACGW, outcompeting native parasitoids. This outcome should be considered as beneficial through the maintenance of ecological balance in affected forest ecosystems.