Exposure to insecticide drift in a buckwheat insectary strip does not negatively affect survival of Trissolcus japonicus, a parasitoid wasp

The incorporation of flowering insectary strips along crop field margins attracts and retains beneficial insects in agroecosystems. For parasitoid wasps, a high-quality nectar-source increases fecundity and longevity, increasing biological control potential. However, the positive effects of insectary strips may be offset if beneficials are exposed to considerable insecticide spray. In this experiment, we planted buckwheat across from orchards and applied three insecticide treatments to the flowers: direct spray with Actara (Thiamethoxam), no spray, and a drift treatment where only neighboring peach trees were sprayed. We quantified insecticide drift by placing SpotOn cards that change color when exposed to liquid in the buckwheat. Next, we investigated how insecticide drift affects survival of Trissolcus japonicus, a parasitoid that is the main candidate for classical biological control of the invasive pest Halyomorpha halys. W introducing flower sprigs to wasps in vials. T. japonicus were equally likely to survive to day three in the control and drift treatments and 2.4 times more likely to survive in those treatments compared to the directly sprayed buckwheat treatment (0.73 vs. 0.30 survival probability). Interestingly, T. japonicus exposed to directly sprayed buckwheat were about 4.3 times more likely to survive to day three compared to T. japonicus exposed to directly sprayed peach leaves and no buckwheat (0.30 vs. 0.07 survival probability). Our results suggest that buckwheat strips fit into growers’ existing management regimes, as insecticide drift does not alter survivorship of a key parasitoid. Furthermore, access to buckwheat nectar may delay lethal effects of insecticides for parasitoids.