Using Accumulated Heat Units to analyze Climate Impacts on Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) Larval Development in Response to Climate Change Scenarios

The study evaluates the impact of climate change on the larval development duration of Spodoptera frugiperda (fall armyworm) across three Egyptian governorates— at Ismailia (Lower- Egypt), El Fayoum (Middle Egypt), and New Valley (Upper Egypt) Governorates—between 2022 and projected scenarios for 2030 and 2050. . Climate change data from the HadCM3 model was utilized, focusing on A1 scenarios recommended by the Intergovernmental Panel on Climate Change (IPCC). In 2022, larval development durations ranged from 26.75 ± 8.53 days in Ismailia (365.23 ± 3.16 Degree Days Units [DDUs]) to 22.8 ± 4.12 days in El Fayoum (369.55 ± 4.57 DDUs), and 17.12 ± 2.03 days in New Valley (371.06 ± 3.52 DDUs). With rising temperatures, by 2030, development times are projected to decrease to 23.36 ± 8.02 days, 20.45 ± 4.25 days, and 16.86 ± 3.36 days in these regions, respectively, while DDUs slightly increase. By 2050, larval development will further accelerate, with durations of 21.33 ± 5.63 days in El Ismailia, 19.36 ± 3.44 days in El Fayoum, and 17.06 ± 3.94 days in New Valley. Seasonal data highlight the shortest development times during peak summer months (e.g., 14 days in July in New Valley, 15–18 days in other regions) and longer durations during cooler periods. Degree-day analyses reveal higher thermal unit accumulation in New Valley, reflecting its hotter climate. Projected climate scenarios show faster development times, particularly in hotter regions, with implications for increased pest generations and heightened crop damage risk. The study underscores regional differences in pest behavior, highlighting the need for localized pest management strategies under changing climatic conditions.