Banana Weevil (Cosmopolites sordidus) Infestation: Causes, Symptoms, and Control

Introduction

The banana weevil (Cosmopolites sordidus) is a serious pest affecting banana crops worldwide. The infestation begins at the base of the dying outermost leaf sheath and spreads to the pseudostem, rhizome, and roots, causing extensive damage. This article provides insights into the causes, symptoms, and management strategies for controlling banana weevil infestations.

1. Cause of Infestation

• The banana weevil lays eggs at the base of the pseudostem and in injured plant tissues.
• Larvae bore into the pseudostem base, rhizome, suckers, and roots, creating tunnels.
• Fungal decay follows, reducing the corm to a blackened mass.
• Infestation weakens the plant, making it prone to toppling in strong winds.

2. Symptoms of Damage

• Infested plants have dull yellow-green, floppy foliage.
• Young infested suckers wither and fail to develop.
• Severely affected plants are stunted and produce smaller fruits.
• Older plants appear tall and spindly due to slow, gradual insect attacks.
• Symptoms observed include toppling, snapping, splitting, leaning, stunting, and reduced fruit size.
• In high winds, infested plants fall easily, leading to significant losses.
• Infestation can also be linked to bacterial rhizome head rot (Erwinia carotovora).

3. Infestation Spread

• Banana weevil populations increase when infected rhizomes are planted.
• Larvae feed and tunnel between lateral roots and the corm, accelerating plant decline.
• Harvesting methods can influence infestation levels; random cutting of pseudostems allows weevils to breed continuously.

4. Control and Management

Cultural Control

• Harvest mature pseudostems at fixed intervals to disrupt the weevil’s breeding cycle.
• Destroy stumps of wind-damaged plants to prevent further infestation.
• Avoid replanting previously infested areas until old corms are completely removed.
• Maintain a cover crop to minimize soil erosion while waiting for weevil populations to decline.
• Remove old corms, trash, and other breeding sites to lower weevil numbers.
• Regularly desucker and remove water suckers to reduce infestation risks.

Mechanical Control

• Use split pseudostem and disc-on-stump traps to monitor adult weevil populations.
• Continuous trapping over a year can reduce weevil populations by up to 50%.
• The "count, cut, and dry" method involves cutting harvested pseudostems into 60 cm lengths, splitting them, and allowing them to dry to prevent larval survival.

Chemical Control

• Insecticides are applied to the plant base for effective control.
• Treat rhizomes before planting by peeling lesions and immersing them in hot water (54°C for 10 minutes) to kill weevil eggs and larvae.

Biological Control

• Predators can help control banana weevil larvae.
• Cutting residual stumps after harvest enables natural predators to reach larvae earlier.

5. Life Cycle and Environmental Factors

• Egg incubation period: 3-5 days.
• Larval stage duration: 21-23 days.
• Pupal duration: 8-10 days.
• Adult lifespan: 65-200 days in laboratory conditions.
• Developmental threshold: 12°C, with an optimal temperature range of 25-30°C.
• High humidity (>70%) and temperatures between 25-35°C favor weevil activity.
• Activity slows in cooler and drier conditions.

Conclusion

The banana weevil poses a major threat to banana cultivation. Effective control involves cultural, mechanical, chemical, and biological strategies. Proper field sanitation, timely harvesting, and preventive measures can significantly reduce weevil infestations, ensuring better banana yields.