Rice Weevil (Stored Grain)

📖 Description

Rice Weevil (Sitophilus oryzae) is one of the most destructive storage pests of rice, wheat, maize and other cereals across the Indian subcontinent, responsible for post-harvest losses of 20-50% in untreated stored grain. The pest is unusual among storage pests in being able to fly (unlike the granary weevil Sitophilus granarius), allowing it to infest grain in the field before harvest and to disperse between storage structures. The adult female lays eggs inside grain kernels, sealing the egg chamber with a gelatinous plug — the entire larval and pupal development occurs inside the grain, making detection difficult until adults emerge through characteristic ‘window’ holes. A single female can lay 300-400 eggs, and a generation can be completed in 25-35 days under optimal conditions — meaning a small initial infestation can explode to devastating levels within months of storage. Beyond direct weight loss, the pest reduces germination of seed grain (making it unusable for planting), produces a characteristic sweetish odour that downgrades grain quality, and causes heating and moisture buildup that favours mould growth and mycotoxin contamination. IPM with thorough sun-drying before storage (kills eggs and larvae), hermetic storage using Purdue Improved Crop Storage (PICS) bags (most effective preventive measure — creates low-oxygen environment that kills all stages), activated clay or neem oil treatments, and biological control with parasitic wasps (Anisopteromalus) provides effective and sustainable control. The PICS bag program has been transformative across India — these triple-layered hermetic bags eliminate the need for chemical fumigation and preserve grain quality for 6+ months.