Seasonal incidence and bio-ecology of fall armyworm on maize in tropical lowlands

Abstract:

Since its first detection in India in 2018, the fall armyworm (Spodoptera frugiperda J.E. Smith) has established itself as a persistent threat to maize cultivation across the country, but its seasonal population dynamics in the humid subtropical lowlands of northeast India have not been characterized. This research recorded the monthly incidence, life table parameters, and natural enemy activity of fall armyworm on maize at the Instructional-cum-Research Farm of Assam Agricultural University, Jorhat, during the kharif seasons of 2022 and 2023. Larval populations peaked in August at 22.6 per 10 plants, coinciding with maximum temperature (28.8 °C) and relative humidity (91.3%). Egg mass density peaked one month earlier in July at 8.4 per 10 plants. The total developmental period from egg to adult averaged 41.0 ± 3.8 days under field conditions. Larval parasitism by Cotesia marginiventris and Chelonus insularis reached 16.8% at peak season. Fecundity averaged 846 eggs per female. Multiple regression showed that temperature and relative humidity together explained 78.4% of the variation in larval population. These baseline bio-ecological data provide the foundation for developing locally calibrated forecasting models and IPM schedules for fall armyworm in northeastern India.