Sweet Potato Weevil (Cylas formicarius): The Tiny Pest That Turns Sweetness Bitter

In tropical agriculture, sweet potatoes are a valuable staple and economic crop. However, lurking beneath their sweetness is a silent yet destructive enemy—the Sweet Potato Weevil (Cylas formicarius). Though just a few millimeters long, this pest can cause damage far beyond its size, and it remains one of the most difficult threats to control in sweet potato farming.

Meet the Culprit: What Is the Sweet Potato Weevil?

• Scientific name: Cylas formicarius (Fabricius)
• Family: Brentidae
• Order: Coleoptera (beetles)

Key features:

• Slender body, measuring around 5.0–6.5 mm long
• Shiny metallic blue wing covers (elytra)
• Reddish-brown thorax and legs, making them visually striking
• A distinct downward-curving snout used to bore into plant tissue and lay eggs
• Elbowed antennae and long, slender walking legs

Though almost beautiful under magnification, this weevil is a stealthy destroyer of root crops—especially sweet potatoes.

Life Cycle: Short, Fast, and Harmful

The Sweet Potato Weevil undergoes complete metamorphosis, cycling through four stages in just two months:

• Egg stage: ~7 days
• Larval stage: ~28 days – larvae tunnel inside the tuber, feeding on plant tissue
• Pupal stage: ~7 days – pupation occurs silently underground
• Adult stage: lives for about 42–43 days, continuing the reproductive cycle

Damage: Turning Sweet into Bitter

The true danger of Cylas formicarius lies not just in physical destruction but in degrading the food quality of sweet potatoes:

• Adults chew into leaves, vines, and tuber surfaces
• Larvae burrow through the flesh, leaving winding tunnels
• Infested tubers emit a foul odor, develop bitterness, and become inedible
• Severe infestations can rot entire fields, making harvests worthless

Even minor damage can render crops unsellable due to changes in taste, smell, and appearance.

Host Plants and Spread

• Primary hosts: Sweet potatoes (Ipomoea species) and related plants in the Convolvulaceae family, such as water spinach
• Global distribution: Common across tropical regions worldwide, especially in areas with intensive sweet potato cultivation

Effective Pest Management Strategies

✅ 1. Cultural Control

• Avoid planting in previously infested fields
• Rotate crops with unrelated plant families
• Use certified pest-free sweet potato vines
• Remove weeds belonging to the same botanical family

✅ 2. Chemical Control

Apply insecticides such as:

• Carbosulfan (Posse 20% EC) – 100 ml per 20 liters of water
• Fipronil (Ascend 5% SC) – 20 ml per 20 liters of water Apply according to safety guidelines and local regulations.

✅ 3. Biological Control

• Use natural enemies such as parasitoid wasps, predatory insects, or entomopathogenic fungi (e.g., green muscardine fungus) to target larvae

Conclusion

The Sweet Potato Weevil may be small, but its impact on agriculture is immense. It doesn’t just eat crops—it ruins their quality, tarnishes their reputation, and affects market confidence. Comprehensive pest control, from planting to post-harvest, is essential to protect sweet potato production and ensure a safe, marketable harvest.