Flowering buckwheat supports Trissolcus japonicus and Trissolcus mitsukurii egg parasitism on Halyomorpha halys

Habitat management using inter-row flowering plants can be a strategy for the promotion of biological control of fruit crops pests. In the present study, we investigated the effect of inter-row ground cover management in supporting Trissolcus japonicus and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae), egg parasitoids of the invasive Halyomorpha halys Stål (Hemiptera: Pentatomidae), a major pest in fruit crops worldwide. In a two-year field study, we evaluated H. halys abundance and parasitism by T. japonicus and T. mitsukurii in a kiwifruit orchard in three different inter-row ground cover managements characterized by the use of different flowering plants: buckwheat, a nectar-providing plant known for its beneficial effect on Trissolcus wasps; a commercial green manure mixture of ten plant species, four of them known to provide nectar for parasitoids and a control with mowed spontaneous vegetation. The results showed that buckwheat improves the parasitism of adventives Trissolcus on H. halys eggs (on both natural and sentinel eggs). An improved parasitism on sentinel egg masses was also observed in green manure during the first year of the study, but the greater diversity of plant species in green manure plots caused an increase of egg masses laid on kiwifruit by other stink bugs species. Although the finite rate of increase of H. halys population decreased with higher levels of Trissolcus parasitism, the overall pest population on kiwifruit remained consistent across different ground cover managements. The results obtained here highlighted that adding flowering plants, in particular buckwheat, can promote egg parasitism on H. halys and represent a potential tactic to be included in integrated management strategies of this pest in fruit orchards.