First Record of Biocontrol Agent Torymus sinensis (Hymenoptera; Torymidae) in Bosnia and Herzegovina

Background and Purpose: Dryocosmus kuriphilus is an invasive insect species of sweet chestnut (Castanea spp.) originating from China, and the only effective control measure against this pest is classical biological control with introduced parasitoid Torymus sinensis. This parasitoid has been widely released in many European countries, but it also has the ability to rapidly spread naturally. No official releases have been done in Bosnia and Herzegovina. Material and Methods: D. kuriphilus galls were collected in July 2017 on 6 localities in forest district Unsko (Una Sana canton) in Bosnia and Herzegovina. Presence and parasitism rates of T. sinensis were recorded in the entomological laboratory, Croatian Forest Research Institute. T. sinensis larvae were identified morphologically and by being compared with the voucher specimens. Results and Discussion: Torymus sinensis larvae were positively identified in the examined D. kuriphilus galls from all localities in Bosnia and Herzegovina. Parasitism rates ranged from 44.83 to 74%. Occurrence and high parasitism rates in Bosnia and Herzegovina observed in this study are not results of biocontrol releases of T. sinensis, but can be attributed to natural spread from Croatia. High parasitism rates observed in this study can indicate that the parasitoid was present in Bosnia and Herzegovina in 2016. Conclusions: This study presents the first record of Torymus sinensis in Bosnia and Herzegovina. We predict that the parasitoid will continue its spread over Bosnia and Herzegovina in sweet chestnut forests and orchards and that it will act as effective biological control agent against D. kuriphilus.