Evaluations of drone based pesticide spraying effects on pollinators and natural enemies in brinjal (Solanum melongena L.) ecosystem

Abstract

In horticultural ecosystems, preserving beneficial insect biodiversity is essential for safe and effective pest control through biological means, offering a safer alternative to chemical pesticides. This study evaluated the biosafety of various insecticides on natural enemies and pollinators in brinjal crops during the rabi seasons of 2022-23 and 2023-24, comparing drone-based and conventional spraying methods. Key predatory arthropods observed included spiders, ladybird beetles, and mantids, while pollinator species identified on brinjal flowers were Bombus sp., Xylocopa sp., Apis mellifera, and Apis cerena. Results showed that both drone and conventional spraying methods were equally safe for natural enemies, with population increases observed across all drone treatments. Specifically, T3 (50% RDP via drone) led to a 19.84% increase over T4 (100% RDP via knapsack), T2 (75% RDP via drone) resulted in a 16.27% increase, and T1 (100% RDP via drone) showed a 14.29% increase. Drone treatments also proved less harmful to pollinators, preserving diversity without reducing flower visitation rates, which peaked in the morning (07:00–11:00 am) and tapered off by late afternoon (14:00–18:00 pm). Pollinator diversity was highest in the untreated control group (H = 1.00), followed by T3 (H = 0.98), T2 (H = 0.96), and T1 (H = 0.95), with the lowest diversity recorded in conventional spray treatments (H = 0.79).