Field efficacy of the pupal parasitoid Chouioia cunea Yang, 1989 (Hymenoptera: Eulophidae) and selected insecticides for management of Hyphantria cunea (Drury, 1773) (Lepidoptera: Erebidae) in hazelnut orchards

The fall webworm, Hyphantria cunea (Drury, 1773) (Lepidoptera: Erebidae), is a destructive polyphagous pest that poses a serious threat to hazelnut production worldwide. Effective management strategies are critical for minimizing its economic impact. This study aimed to evaluate the field efficacy of the pupal parasitoid Chouioia cunea Yang, 1989 (Hymenoptera: Eulophidae) and three insecticides ‒Bacillus thuringiensis var. kurstaki, azadirachtin, and diflubenzuron‒ applied in hazelnut orchards in Düzce province of Türkiye, between 2020 and 2021. To evaluate their distinct life-stage efficacies, larval mortality was assessed using a randomized complete block design following insecticide treatments targeting early instars, and pupal parasitism was assessed using a randomized plots design across two generations following parasitoid releases. Releases of C. cunea significantly increased pupal parasitism rates, reaching 86.06% in 2020 and 94.95% in 2021, compared to those in the untreated control plots. All insecticide treatments significantly suppressed larval populations, with B. thuringiensis and diflubenzuron consistently achieving higher efficacy than azadirachtin. In 2020, these two insecticides achieved efficacy levels exceeding 77%, while azadirachtin remained below 68%. In 2021, all insecticides showed improved performance, surpassing 90%, although azadirachtin remained slightly less effective. These findings support the potential of utilizing both biological control agents and selective insecticides as complementary tools within a sustainable and environmentally friendly strategy for managing H. cunea in hazelnut orchards.