Native parasitoids recruitment as potential controllers of Dryocosmus kuriphilus (Hymenoptera; Cynipidae) in recently colonised areas

Abstract

In this work, we investigate the native parasitoid community colonising galls by an invasive pest: the oriental chestnut gall wasp (OCGW), Dryocosmus kuriphilus (Hymenoptera; Cynipidae). We tried to understand how native parasitoids react after the arrival of the pest (two-year sampling period) in the province of Zamora (Castilla & León region, N-W Spain). For this purpose, we collected both, chestnut galls from six stands and oak galls from surrounding oak groves. Our results highlight the response to D. kuriphilus provided by the oak gall wasps that naturally inhabit Quercus pyrenaica. The parasitoid community showed a core assemblage composed of Eurytoma brunniventris, Torymus flavipes and T. sinensis in OCGW galls, and Baryscapus diaphantus, Bootanomyia dorsalis, Eupelmus urozonus, E. brunniventris, Mesopolobus lichtensteini, T. affinis, and T. flavipes in oak galls. We identified the torymid T. flavipes as one of the most common parasitoids of OCGW, in addition to the exotic parasitoid T. sinensis, never officially released in the region but present in the study area. In addition, we intend to know its possible incidence on non-target cynipids. We have found an intense connection in the food web with some chalcids that establish interactions with the gall wasp, both in adult instar (emerging from reared galls) and larval (presence of larvae in OCGW gall chambers, identified by dissection). We also describe the flight phenology of D. kuriphilus in our study area (as far as we know, the first one focused in Castilla & León region) and evaluate the overlap between OCGW and native and exotic parasitoids showing a promising role of native guild as biocontrollers.