Bean Weevil (Acanthoscelides obtectus): The Silent Intruder Inside Every Seed

If you're storing kidney beans, mung beans, or any legume crop, there's one stealthy pest that can quietly destroy your inventory from the inside out—the Bean Weevil (Acanthoscelides obtectus). Small in size but powerful in impact, this beetle feeds within the seed, degrading quality, reducing market value, and leaving only hollow shells behind.

Without proper control, a single infestation could force you to discard entire batches of beans—often before you even notice the damage.

Know Your Pest: What Is the Bean Weevil?

• Common name: Bean Weevil
• Scientific name: Acanthoscelides obtectus (Say)
• Family: Chrysomelidae
• Order: Coleoptera

Key features:

• Size: 3.0–4.5 mm
• Color: Grayish-brown to dark brown, unmarked body
• Short, hardened forewings (elytra) covered with yellow-gray hairs
• Subserrate (semi-sawtooth) antennae
• Rear legs equipped with 2–3 small spines and one larger spine at the base for climbing and gripping

Life Cycle: Fast and Fertile

The Bean Weevil undergoes complete metamorphosis, completing one life cycle in 31–44 days:

• Egg stage (5–6 days): Each female lays 100–200 eggs in seed cracks or rough surfaces
• Larval stage (20–27 days): Larva bores into the seed and feeds internally
• Pupal stage (6–11 days): Pupa develops inside the seed
• Adult stage (7–14 days): Mates and lays eggs rapidly before dying

Despite their short lifespan, these insects can multiply quickly and silently within storage areas.

Preferred Food Sources

The Bean Weevil attacks a wide range of leguminous crops, including:

• Kidney beans
• Mung beans
• Bush beans
• Yardlong beans
• Lima beans

Damage Symptoms: Small Holes, Big Losses

• Eggs are laid on the seed surface or inside small surface cracks
• Larvae feed from within, hollowing out the bean completely
• Just before pupation, the larva creates a “window” by thinning the seed coat from inside
• Adults emerge through small round holes, leaving visible damage
• Infested seeds lose weight, become brittle, and are more prone to mold

Distribution

Bean Weevils are widespread in tropical and temperate regions across the globe—
With the notable exception of Australia, where infestations are rare or absent.

How to Prevent and Control Bean Weevil Infestations

✅ Warehouse Hygiene

• Clean storage floors and corners regularly
• Remove spilled beans and dust—prime egg-laying sites for weevils

✅ Temperature Control

• Use extreme heat or cold to halt development
• Best applied in sealed rooms or bulk grain silos

✅ Fumigation

• Ideal for long-term storage or pre-export treatment
• Kills eggs, larvae, and pupae hidden inside beans

✅ Pheromone Traps

• Capture adults to reduce mating and egg-laying
• Serve as effective tools for monitoring and outbreak control

Conclusion

The Bean Weevil may live just a few days, but in that time, it can silently destroy the quality of your entire bean inventory. Internal damage is often invisible until it's too late. Understanding its biology and enforcing strict pest control measures from the start is essential for protecting every sack of beans and preserving product value.