Botanical-Based Granular Insecticides for Sustainable Management of Sitophilus oryzae in Stored Rice under Seasonal Conditions

Abstract

The rice weevil, Sitophilus oryzae (L.), is a predominant stored grain pest responsible for substantial quantitative and qualitative losses in stored cereals.  This study investigated the efficacy of botanical-based granular bioinsecticides against S. oryzae in stored rice. Granules formulated with diatomaceous earth, powdered botanicals (neem, clove, cinnamon, nutmeg), and eucalyptus oil were evaluated at 0.34g, 0.60g, and 1.05g per 20g of rice under both winter and summer conditions.  Phytochemical profiling of the granules was conducted using GC-MS and FTIR analyses confirmed the presence of key bioactive compounds, including eugenol, azadirachtin, cinnamaldehyde, and 1,8-cineole. Laboratory bioassays were conducted to evaluate the efficacy of 3 botanical-based granule biopesticides (0.34g, 0.60g, and 1.05g per 20g rice) under controlled winter and summer environmental conditions. The highest dosage (1.05g) resulted in a significant increase in mortality rates (100%) and a marked reduction in grain weight loss and damage indices compared to controls (p < 0.05). In addition, the treatment effectively inhibited F₁ progeny emergence during summer and provided maximum grain protection of 100.00% and 98.28% under summer and winter storage conditions respectively. Seasonal variation indicated enhanced efficacy under higher temperature regimes. These findings substantiate the potential of plant-derived granular formulations, combined with diatomaceous earth, as sustainable and environmentally benign alternatives for managing S. oryzae infestations in stored rice grains.