Degree of insecticide exposure and access to nectar impact survival of <i>Trissolcus japonicus</i> , a hymenopteran parasitoid, in flowering border strips

Abstract Incorporating flowering border strips along crop field margins can support natural enemy populations, which increases pest control and may reduce insecticide loads. However, the effect of border strips may be reduced by insecticide drift exposure. We planted buckwheat strips across from managed peach orchards and applied three insecticide treatments: direct spray with thiamethoxam, no spray, and an insecticide drift treatment, where only neighbouring peaches were sprayed. We quantified drift by placing colour‐changing cards in the buckwheat. Drift treatment cards had an average coverage of 1.39%, which was significantly lower than that of directly sprayed cards (99.86%). However, drift cards also had significantly greater coverage than unsprayed control cards (average coverage: 0.01%). We investigated how insecticide drift affects survival of Trissolcus japonicus (Hymenoptera: Scelionidae), a parasitoid that provides biological control of the invasive pest Halyomorpha halys (Hemiptera: Pentatomidae). Parasitoids were equally likely to survive to 24‐ and 48‐h in arenas with buckwheat from the unsprayed control and drift areas, and insects had significantly higher survival probability than parasitoids provided directly sprayed plant material. In arenas with control buckwheat and a sprayed peach leaf and arenas with directly sprayed buckwheat, T. japonicus had significantly higher survival probability than T. japonicus in arenas with a sprayed leaf only, indicating that nectar access prolongs survival after insecticide exposure. Our results suggest that buckwheat border strips are complementary to growers' existing management programs, as insecticide drift does not alter survivorship of a key parasitoid.