Armyworm population dynamics and damage assessment in rice agroecosystems at Jampuijala, Tripura, India

Abstract

Rice cultivation faces persistent challenges from various insect pests, including invasive species. The emergence of four armyworm species (rice swarming caterpillar, Spodoptera mauritia (Boisduval), common cutworm, Spodoptera litura (F.); rice ear-cutting caterpillar/paddy armyworm, Mythimna separata (Walker); and fall armyworm, Spodoptera frugiperda (J.E. Smith), along with other herbivores, poses significant threats to Asian rice ecosystems, causing considerable economic losses. This study investigates the occurrence and distribution of these armyworm species in rice agro-ecosystems across three Village Councils (VCs). Only S. mauritia larvae were observed, appearing in nursery fields approximately16-27 days after sowing and displaying sudden mass attacks primarily targeting seedlings at the 1-5 leaf stages. Damage manifestations included cutting leaf tips, creating shot holes on leaf blades, and occasionally severing seedlings at the base. The Ranjit variety in Kalaibari VC and the Gomati variety in Killa Verma VC showed the highest infestation rates (18.0%) and larval populations (1.7 larvae/m2). These findings offer valuable insights for stakeholders involved in rice cultivation across Asian rice-producing nations. Keywords: Oryza sativa, Spodoptera mauritia, Spodoptera frugiperda, Spodoptera litura, Mythimna separata.