Rice Weevil (Sitophilus oryzae)

The Silent Pest Threatening Global Grain Storage

The Rice Weevil, also known as the Grain Weevil (Sitophilus oryzae), is one of the most common and destructive pests of stored cereals worldwide, particularly in tropical and subtropical regions like Southeast Asia and Thailand. Despite its tiny size, this beetle causes serious quantitative and qualitative losses, especially in long-term seed storage systems.

Taxonomic Classification

• Common Name: Rice Weevil
• Scientific Name:Sitophilus oryzae (Linnaeus)
• Family: Curculionidae
• Order: Coleoptera

Morphological Characteristics

• Elongated snout or rostrum used for boring into grains
• Geniculate antennae (elbowed)
• Elytra (hardened forewings) with fine grooves
• Thorax covered with small dimples

Life Cycle (Complete Metamorphosis)

Total life cycle: ~30–40 days depending on temperature and humidity.

Host Plants & Damage

Primary Hosts:

• Rice
• Maize
• Sorghum
• Barley
• Oats
• Millet and other grains

Damage Profile:

• Larvae bore into and consume the inside of grain kernels
• Leaves behind empty shells with visible exit holes
• Affected grains are unsuitable for consumption or planting
• Does not infest flour; larvae cannot develop in powdery materials

Geographic Distribution

Sitophilus oryzae is widespread in tropical and subtropical climates, particularly in Asia and Africa. It thrives in poorly managed or humid storage facilities, where conditions allow for rapid reproduction and infestation.

Integrated Pest Management (IPM)

✅ 1. Preventive Measures

• Maintain hygiene in storage areas
• Eliminate hiding places in cracks, corners, or under equipment
• Conduct routine inspections of stored grain

✅ 2. Temperature Control

• Use heat (>60°C) or deep freezing to halt development and kill insects

✅ 3. Chemical Control

• Apply fumigation pre- and post-storage
• Suitable for high-risk or contaminated lots (e.g., rejected consignments)

✅ 4. Pheromone Trapping

• Detect and monitor weevil presence
• Helps reduce adult populations in warehouses

✅ Conclusion

The Rice Weevil (Sitophilus oryzae) is a major pest in grain and seed storage industries. Its ability to reproduce inside grains and cause invisible internal damage makes early detection difficult. Adopting a well-rounded IPM approach — including prevention, monitoring, and targeted control — is essential for minimizing post-harvest losses and ensuring sustainable food supply chains.