New Records of Braconidae (Hymenoptera) Parasitoids of Stem Borers (Lepidoptera: Crambidae) in Rice Paddies

Abstract

Extensive field surveys were conducted in rice-growing ecosystems to document the diversity of braconid parasitoids associated with stem borer pests belonging to the family Crambidae. Sampling was carried out across major rice-producing regions during different crop growth stages through collection of infested stems, sweep netting, and laboratory rearing of parasitoids from stem borer larvae and pupae. Morphological examination based on antennal structure, wing venation, body sculpture, ovipositor morphology, and metasomal characteristics revealed the presence of several braconid species representing new regional records from rice paddies. Taxonomic identification was further supported through molecular characterization using mitochondrial cytochrome oxidase I (COI) gene sequencing, confirming phylogenetic placement within recognized Braconidae lineages. The recovered parasitoids were associated primarily with economically important stem borer species infesting rice stems and causing dead heart and whitehead symptoms. Seasonal occurrence of parasitoids showed strong synchronization with host population density, with peak abundance observed during active stem borer infestation periods under moderate temperature and high humidity conditions. Natural parasitism levels varied among sampling locations and cropping seasons, reflecting the influence of environmental factors and agricultural management practices on parasitoid activity. Rice fields managed with lower insecticide inputs supported greater parasitoid diversity and higher parasitism rates compared with intensively treated fields. Certain braconid species demonstrated high adaptability and effective host utilization, indicating their ecological importance as indigenous biological control agents within rice agroecosystems.