Rice Black Bug (Scotinophara coarctata)

The Subtle Root-Feeding Pest That Threatens Rice Fields from Below

During the rice-growing season, many farmers may notice shield-shaped, glossy black bugs clustering near the base of rice plants. These insects are Rice Black Bugs (Scotinophara coarctata), one of the most persistent pests in tropical rice fields. Though slow-moving and small, they cause long-term, cumulative damage that directly impacts both yield quantity and grain quality.

Basic Information

• Common Name: Rice Black Bug, Malayan Black Bug
• Scientific Name:Scotinophara coarctata (Fabricius)
• Family: Pentatomidae
• Order: Hemiptera

Morphology & Biology

• Forewings: Hemelytra (hardened at the base, translucent at the tips)
• Hindwings: Membranous

Behavior

• Clusters near the base of rice plants above the waterline during the day
• Moves upward at night to feed on plant tissues
• Prefers low-light, humid environments under the canopy

Life Cycle (Incomplete Metamorphosis)

• Incubation: 4–6 days
• Eggs are reddish-green, disc-shaped, laid in rows on leaves or sheaths
• Females lay 150–200 eggs

• Development: 20–30 days
• Six instars; brownish-yellow body with black spots

• Lifespan: up to 214 days

Total life cycle: Approximately 2–3 months

Feeding Behavior & Crop Damage

Host Plants: Primarily grasses in the Poaceae family, including:

• Rice
• Corn
• Wild rice
• Weedy grasses such as Echinochloa

Damage Symptoms:

• Feeds by sucking sap from leaf sheaths and basal stems
• Causes stunted growth, dry and brittle leaves, and browning margins (often mistaken for blast disease)
• During grain-filling: panicles remain underdeveloped, producing empty grains
• Severe infestations can cause wilting and plant death

Distribution

Widespread across tropical and subtropical rice-growing regions, particularly in:

• Thailand
• The Philippines
• Indonesia
• India
• Vietnam

Management and Control Strategies

✅ Use Light Traps

• Rice black bugs are strongly attracted to light at night
• Install light traps to lure and destroy them

✅ Plant Short-Duration Rice Varieties

• Reduces exposure time and disrupts the pest's reproductive cycle

✅ Weed Management

• Remove weeds in and around rice paddies
• Improves sunlight penetration and reduces humidity at the plant base, making conditions less favorable for bugs

✅ Regular Field Monitoring

• Especially important from maximum tillering to pre-harvest
• If more than 5 bugs are observed per hill, take action immediately

✅ Targeted Chemical Control

• Use Carbosulfan (Pos 20% EC)
• Mix 80 mL per 20 liters of water
• Apply directly at the base of affected plants

✅ Conclusion

Though small and slow-moving, the Rice Black Bug (Scotinophara coarctata) is far from harmless. Its ability to extract nutrients from the base of rice plants can lead to significant cumulative damage if left unchecked. An integrated approach—combining mechanical, biological, and chemical methods—is essential for long-term, sustainable management of this damaging pest.