Rice Black Bug (Scotinophara coarctata) | Root-Damaging Pest in Tropical Rice Fields
Tags: rice black bug, scotinophara coarctata, rice pest, root-feeding insect, hemiptera pest, tropical rice pests, ipm rice, rice bug control, carbosulfan, sustainable rice farming
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
Body Length: 7–8 mmShape: Shield-shaped; head and thorax triangular
Color: Dark brown to shiny black
Antennae: Filiform (thread-like)
Wings:
- 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)
Egg Stage:- 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.
Rice Black Bug (Scotinophara coarctata) — 3 High-Intent, Google-Style FAQs
Q: 1 How do I quickly confirm that the black bugs at the base of my rice are rice black bugs (not stink bugs or planthoppers)?
A: Look at where and when they feed: rice black bugs cluster at the plant base by day and climb up to feed at night. Adults are shield-shaped, glossy dark brown–black, ~7–8 mm, with smooth legs (no spines) and filiform antennae. Eggs are disc-shaped, reddish-green laid in rows on leaves/sheaths; nymphs are brownish-yellow with black spots. Damage shows as browning leaf margins, brittle leaves, and underfilled panicles—often misread as blast, but you’ll find active bugs at the basal sheath if you part the hills.Q: 2 What’s the best timing and method to control rice black bugs without wiping out beneficials?
A:- Scout first: From maximum tillering → booting/grain fill, check 10 hills per field edge + center. >5 bugs per hill = intervene.
- First line: Light traps at field edges (dusk–dawn) for mass-attract/kill; weed control on bunds and margins to reduce humid refuges.
- Cultural: Prefer short-duration varieties to shorten exposure; avoid synchronized back-to-back rice that lets populations carry over.
- Targeted spray (if over threshold): Direct a basal spray to leaf sheaths with Carbosulfan 20% EC at 80 mL/20 L water; treat hot spots/patches, not blanket, and rotate MOAs in subsequent sprays. Spray late afternoon/evening when bugs move up, and keep nozzles angled to soak the lower sheath.
Q: 3 Why do fields still decline after spraying, and how can I prevent re-infestation?
A:1) Missed habitat: Bugs hide under dense canopies and in weedy grasses (e.g., Echinochloa); if weeds remain, populations rebound.
2) Basal feeding: Canopies get sprayed while the basal sheath stays dry—retarget coverage to the base.
3) Staggered generations: With 6 nymphal instars and adults living months, a single spray rarely collapses the cohort.
4) Fix the system:
- Dry and flush as per water schedule to reduce humidity at the base.
- Harvest promptly and remove stubble refuges; plow in residues or compost away from paddies.
- Edge management: keep levees clean; run light traps 3–5 nights post-spray to intercept survivors.
- Re-scout in 5–7 days; if still >threshold, rotate chemistry and spot-treat only where needed.
Bottom line: Identify at the basal sheath, hit threshold-based, basal-focused controls, and pair light/weed/variety tactics with tight re-scouting to keep rice black bugs below damaging levels—without overusing insecticides.
