Banana Scab Moth (Nacoleia octasema)

The banana scab moth, a member of the family Crambidae, is a significant pest in banana production. Its feeding damage causes severe cosmetic defects on fruit, often leading to downgrading or outright rejection in the market, resulting in substantial economic losses.

Identification

• Adult Moth:
  Small, with a wingspan of 25–30 mm, tan to light brown in colour, and marked with fine black spots on the wings.

• Eggs:
  Flattened and laid in clusters of up to 30 eggs, resembling shiny, overlapping fish scales. They are usually deposited on or near emerging banana bunches.

• Larvae:
  Yellow to orange caterpillars that grow to about 25 mm before pupation.

Life Cycle

The banana scab moth completes its life cycle in approximately 28 days under warm, wet conditions.

1. Egg Stage:
   Eggs hatch in about 4 days, and the young larvae immediately move underneath the tightly closed bracts to feed on developing fruit.

2. Larval Stage (5 instars):
   Larval development takes roughly 14 days. As bracts progressively lift, larvae move to the next tightly closed hand. They primarily remain under bracts near the distal male flower bud.

3. Pupation:
   Larvae spin thin silken cocoons mixed with debris for camouflage. Pupation occurs either on the bunch, in plant trash, or within old leaf axils of the pseudostem. The pupal period lasts 8–10 days.

4. Adult Stage:
   Adults live for 4–5 days, are crepuscular, and engage in mating and egg laying during early evening hours. During the day, moths hide under old leaf axils or plant debris.

Damage

• Newly emerged larvae migrate to the bunch and feed on the inflorescences and fruit surface, causing distinct cosmetic scarring, black scabs, and contamination with frass.

• In severe cases, larvae penetrate the peel and feed on the pulp.

• Feeding typically occurs in sheltered areas under unsheathing bracts; as bracts lift, larvae move downward to protected hands.

• If development is not complete when the last bract falls, larvae may:

  • Remain in the bell feeding on male flowers, or

  • Migrate back up the bunch to feed on maturing fruit.

The pest is most destructive during hot, wet weather, and severe infestations can cause substantial yield and quality losses.

Control Strategy

Effective management of the banana scab moth requires an integrated approach combining chemical, biological, and cultural methods.

1. Chemical Control

The following insecticides are recommended:

• KINGCODE ELITE 50 EC – 10 ml / 20 L

• PENTAGON 50 EC – 10 ml / 20 L

• LEXUS 247 SC – 8 ml / 20 L

• LEGACY 50 EC – 15 ml / 20 L

• PRESENTO 200 SP – 5 g / 20 L

• ESCORT 19 EC – 10 ml / 20 L

2. Biological Control

• BACIGUARD 16 WDG – 15 g / 20 L
  A biological insecticide based on Bacillus thuringiensis (Bt). It works by colonizing the moth larvae and causing mortality through bacterial infection.

3. Cultural / Non-Chemical Methods

Effective farm management practices include:

• Crop rotation with non-host plants

• Maintaining strict field hygiene and sanitation

• Proper weed management

• Planting tolerant banana varieties

• Conserving natural enemies such as parasitic wasps

Important Tips

• Always mix insecticides with INTEGRA (3 ml / 20 L) to enhance adhesion, spreading, and penetration, thereby improving overall efficacy.

• Timely application is essential—target early stages for best results.

• To prevent resistance development, alternate different classes of insecticides throughout the growing season.

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