Population Dynamics of Certain Insect Pests of Brown-top Millet and Their Natural Enemies

Abstract

Browntop millet is an under-researched small millet for which field information on insect pest succession is limited. A two-season observational study was conducted at the Zonal Agricultural Research Station, University of Agricultural Sciences, Bengaluru, during Kharif 2023 and 2024. A 3 × 4 m plot of the variety GPUBT-1 was monitored weekly from 15 days after sowing to harvest. Shoot-fly damage was expressed as dead-heart incidence, while weevils, grasshoppers, aphids, coccinellids, and spiders were recorded using plant-, leaf-, or row-based counts. In 2023, shoot-fly dead-heart incidence increased from 23.67% in the 36th standard meteorological week (SMW) to a maximum of 30.25% in the 38th SMW and then declined to zero by the 44th SMW. In 2024, incidence increased from 28.67% in the 28th SMW to 48.23% in the 30th SMW and declined to zero by the 36th SMW. Peak weevil abundance was 0.89 per plant in both seasons. Peak grasshopper and aphid abundances were 0.56 per metre of row and 0.56 per leaf, respectively. Coccinellids reached 0.44 per plant in both seasons, while spiders peaked at 1.00 per plant in 2023 and 0.69 per plant in 2024. Exploratory same-week correlations between dead-heart incidence and minimum temperature differed in direction between seasons (r = 0.722 in 2023 and r = -0.744 in 2024). Because the data came from a single field plot with serial weekly assessments, these coefficients were interpreted descriptively rather than as confirmatory tests. The observations indicate that shoot-fly injury was concentrated during the early crop period, whereas secondary pests and natural enemies occurred at comparatively low densities. Multi-location studies with independent plot replication are required before weather-based prediction or economic-loss thresholds can be developed for browntop millet.