Phenology-linked damage dynamics of Halyomorpha halys (Hemiptera: Pentatomidae) on hazelnut orchards in Eastern and Middle Black Sea of Türkiye and Oregon State of the United States: insights for seasonal-adaptive integrated pest management

Brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), severely impacts global hazelnut production, especially in Türkiye, the top producer, and Oregon, USA. This study analyzed seasonal BMSB population dynamics and damage types on hazelnut fruiting bodies across phenological stages. Field monitoring in Oregon's Willamette Valley (2014-2016) and Türkiye's Eastern Black Sea region (2019-2021) showed distinct seasonal activity patterns. Hazelnut phenology in Türkiye advances 6 weeks earlier than in Oregon with higher heat accumulation sustaining BMSB activity post-harvest. Semi-field cage experiments conducted in 2022 in Türkiye quantified insect-induced damage in relation to nut development. Five distinct damage types were identified: shell malformation (4.7%) in May-June, blank black shell (2.2%) and empty kernel (6.5%) in June, shriveled kernel (8.4%) in late June-mid-July, and corked kernel (10.5%) in July-August. A single adult was capable of damaging up to 537 nuts per season, with losses reaching 85% during the kernel expansion stage. Damage increased progressively through the season, with total damage 1.6-fold higher during kernel expansion compared to early development. Corked kernel damage was uniquely associated with BMSB feeding, confirming its diagnostic value. Findings demonstrate that BMSB injury is strongly shaped by the timing of insect activity relative to hazelnut phenology, with peak mid- to late-season activity driving greater losses, particularly in late-maturing cultivars. By linking damage types with per-capita impact, this study defines critical intervention windows for integrated pest management and highlights the need for adaptive forecasting tools that integrate pest biology, climate, and crop phenology.