Maize Weevil (Sitophilus zeamais) – Silent Grain Pest in Global Warehouses
Tags: maize weevil, sitophilus zeamais, grain storage pests, corn weevil control, postharvest pest, warehouse insect, cereal pest, stored grain insect, pest management, fumigation for weevils
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
Antennae: Geniculate (elbowed)Wings:
- Forewings: Hardened (elytra) with fine grooves
- Hindwings: Membranous, enabling strong flight
Legs: Walking legs
Body Length: ~3.0–3.8 mm
Color: Dark brown to black
Distinctive Trait: Elongated snout (rostrum), similar to S. oryzaebut slightly larger and darker
Life Cycle (Complete Metamorphosis)
The maize weevil undergoes 4 distinct developmental stages:
Egg Stage:- 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.-21.jpg)
Maize Weevil (Sitophilus zeamais) — 3 High-Intent, Google-Style FAQs
Q: 1 How can I quickly confirm a maize weevil infestation—and do I need to tell it apart from rice weevil?
A:- Rapid checks: look for pin-size round exit holes, light, dusty frass, and hollow kernels that crush easily. Float-test a sample; severely damaged grains often float from internal tunneling.
- Species look-alikes: S. zeamais (maize) and S. oryzae (rice) are visually near-identical; reliable separation usually needs microscopy. The good news: storage hygiene, drying, hermetic storage, heat/cold, fumigation, and pheromone monitoring are the same for both—so you can act immediately without a species verdict.
- Rule of thumb: if the primary commodity is maize and adults are slightly larger/darker (~3.0–3.8 mm), S. zeamais is likely—treat as a weevil outbreak either way.
Q: 2 What exact moisture/temperature targets kill all life stages (eggs → adults) without ruining grain quality?
A:- Moisture (prevention): dry to ≤12% before storage; aim ≤11% in humid tropics.
- Cold kill (small batches/home): −18 °C (0 °F) for 72–96 h after the core is frozen; for thicker sacks, extend to 5–7 days.
- Heat kill (thin layers/conditioned air or dryer): hold kernels at 60 °C (140 °F) ≥30 min (or 55 °C for ~60 min). Verify with a probe thermometer in the grain center.
- Warehouse scale: use phosphine fumigation only in well-sealed structures and by licensed operators; follow with hermetic storage to prevent reinfestation.
- Monitoring: deploy pheromone traps near doors, conveyors, and quiet corners; log weekly counts to spot rebounds early.
Q: 3 Are weevil-infested grains safe to eat—and what’s the right way to handle contaminated stock?
A:- Food safety: weevils aren’t known to transmit human disease, but tunneling reduces nutrition, raises mold risk, and can trigger allergies.
- Household guidance: for light, fresh infestations, you may freeze-kill, then sieve/rinse and cook thoroughly; discard any musty or off-odor grain.
- Commercial/warehouse practice: do not mix suspect lots with clean stock. Isolate, treat (heat/cold or fumigate), and downgrade or dispose per your QA and buyer specs. After removal, do a deep clean (floors, under pallets, beams, inside panels), restore dry ≤12%, switch to FIFO, and keep traps active to confirm control.
If you share your storage conditions (moisture, temperature, typical hold time), I can tailor a 7-step IPM checklist specific to your site.
