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Banana corm weevil (Cosmopolites sordidus) Photo: placeholder pending image-fill pass

Banana corm weevil (Cosmopolites sordidus)

The banana corm weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), is the principal below-ground pest of banana worldwide and is widespread across all Indian banana-growing states. It is especially damaging in Kerala, the Western Ghats, Assam and the humid laterite belts where moist soils favour larval survival. Adult weevils are nocturnal and rarely seen; damage assessment is therefore based on the characteristic tunnelling of larvae inside the corm.

Identification and symptoms

Adults are 10-15 mm long, shiny black, with the distinctive long rostrum of curculionid weevils. Eggs are laid singly in the leaf-sheath base or in cracks in the corm at the soil-line. The larvae are creamy-white, legless and C-shaped, and tunnel extensively through the corm and the base of the pseudostem. Infested plants show yellowing, stunted growth, premature leaf senescence, smaller bunches and, under heavy attack, lodging of the pseudostem. Cross-sectioning the corm reveals dark, frass-filled tunnels.

Host crops and life cycle

The pest attacks all Musa cultivars including Grand Naine (Banana Grand Naine G9 Jain Tc), Nendran (Banana Nendran Kerala Plantain), Rasthali (Banana Rasthali Silk India), Monthan (Banana Monthan Cooking Plantain), Poovan and Red Banana. Life cycle is 30-40 days under tropical conditions; eggs hatch in 5-8 days, the larval period is 15-20 days, pupation occurs in the corm for 6-8 days, and adults can live for over a year, with low fecundity (one to two eggs per week) but high longevity. Population build-up is favoured by ratoon cropping, sucker-based propagation and infested planting material.

Damage and economic impact

Yield losses of 20-40% are typical in moderately infested plantations; in heavily attacked ratoons of Nendran and Rasthali, losses can exceed 60%. Damaged plants are also predisposed to Fusarium wilt and bunchy top virus because of weakened root systems.

Management

ICAR-NRCB and ICAR-IIHR recommend an integrated package:

  • Clean planting material: tissue-cultured plants or pared and pralined suckers (paring removes weevil eggs; pralinage with clay slurry plus insecticide such as chlorpyrifos coats the corm).
  • Sanitation: prompt removal and destruction of harvested pseudostems and corm residues; avoiding stem heaps near the field.
  • Pseudostem traps: 30-45 cm long split pseudostem traps placed at 100/ha attract and concentrate adults for hand-picking; longitudinally split traps work better than discs.
  • Pheromone traps: aggregation pheromone (sordidin) lures in cross-vane traps at 4-10/ha for monitoring and mass-trapping.
  • Biological: entomopathogenic fungus Beauveria bassiana (1 × 10⁸ spores/g at 50 g/plant) applied to the corm base; soil-application of EPN nematodes (Heterorhabditis indica).
  • Chemical: targeted neem-cake at planting; carbofuran is no longer recommended owing to safety. Where infestation is severe, contact insecticides such as chlorpyrifos may be applied at the corm base under expert advice and label conditions.

See also: Banana Grand Naine G9 Jain Tc, Banana Nendran Kerala Plantain, Banana Monthan Cooking Plantain, Banana Rasthali Silk India, Banana Bunchy Top Virus.

References

  1. Banana corm weevil — management bulletin. ICAR-National Research Centre for Banana, Trichy.
  2. Banana pest profile and IPM recommendations. ICAR-Indian Institute of Horticultural Research, Bengaluru.