First documented economic infestation of Spodoptera frugiperda (J.E. Smith) on sugar beet crop in relation to weather factors in Fayoum Governorate, Egypt

The present study documents the first recorded case of economic infestation by the fall armyworm (Spodoptera frugiperda J.E. Smith) on sugar beet (Beta vulgaris L.) in Egypt, specifically in Fayoum Governorate during the 2020–2021 cropping season. This research aims to estimate population fluctuation and assess the damage caused by the fall armyworm over two growing seasons (2020/2021 and 2021/2022) under the influence of climatic factors. Pest infestation on sugar beet represents an expansion of its host range and presents a new threat to root crop production in Egypt. Farm surveys revealed the highest infestation levels in sugar beet crops near the edges of previously infested maize fields, suggesting likely inter-crop transportation. Larval density peaked during the vegetative state (14–30 larvae per 10 plants), with early instars initiating a "window-pane" type of leaf damage and late instars causing heavy defoliation and whorl destruction. Malva parviflora L. and Chenopodium murale weeds have been identified as alternative hosts, enabling the pest persistence between crop seasons. Statistical analysis established a significant positive correlation between larval density and mean temperature (r = 5.42 × 10⁻¹, p = 4.49 × 10⁻²), indicating that higher temperatures are more conducive to infestation. In laboratory trials, rearing and recording the average incubation period of eggs, larval development, prepupal, and pupal durations were 3.3, 17.6, 2.3, and 8.6 days, respectively. The average fecundity and egg hatchability percentage recorded were 652 eggs/female & 87%, respectively, over a generation time of 34.1 days.