Maize Weevil (Sitophilus zeamais)

The Silent Destroyer in Grain Warehouses Every Farmer Must Know

The Maize Weevil (Sitophilus zeamais) is one of the most destructive insect pests of stored cereals and grains worldwide. Although often mistaken for its close relative, the Rice Weevil (S. oryzae), this species is slightly larger and darker. Infestations can lead to serious quality degradation and economic losses—especially for long-term storage.

Taxonomic Details

• Common Name: Maize Weevil
• Scientific Name:Sitophilus zeamais (Motschulsky)
• Family: Curculionidae
• Order: Coleoptera

Key Morphological Features

• Forewings: Hardened (elytra) with fine grooves
• Hindwings: Membranous, enabling strong flight

Life Cycle (Complete Metamorphosis)

The maize weevil undergoes 4 distinct developmental stages:

• Duration: 3–6 days
• Females lay ~300–400 eggs, each inside a grain kernel

• Duration: 20–30 days
• White, legless larvae feed internally, hollowing out the grain

• Duration: 3–7 days
• Pupation occurs within the grain cavity

• Lifespan: 1–8 months
• Total life cycle: ~30–45 days (temperature and humidity dependent)

Host Grains and Damage

Target Crops:

• Maize (corn)
• Rice
• Wheat
• Sorghum
• Oats
• Barley

Feeding Damage:

• Larvae bore into the grain and consume it from within
• Damaged kernels become hollow with exit holes
• Leads to reduced grain quality, germination rate, and market value

Geographic Distribution

Sitophilus zeamais is widely distributed in tropical and subtropical regions, especially in:

• Southeast Asia (including Thailand)
• India
• Africa
• Latin America

The adults are excellent flyers and breed rapidly, making them difficult to control without proper management.

Prevention and Control Strategies

✅ Sanitation

• Clean warehouses regularly to eliminate food residues and hiding spots

✅ Moisture Management

• Dry grains to below 12% moisture before storage

✅ Temperature Control

• Use heat treatment (>60°C) or cold treatment (<4°C) to kill weevils

✅ Fumigation

• Apply phosphine gas in sealed chambers for effective elimination

✅ Inventory Rotation

• Avoid storing grains longer than 3–6 months

✅ Pheromone Traps

• Monitor and reduce adult populations

Reference

Pornthip Wisartanont et al. (2008). Insects Found in Agricultural Produce and Their Control. Postharvest Technology Research and Development Office, Department of Agriculture, Thailand.