The Mango Nut Weevil, Sternochaetus mangiferae, belonging to the Family Curculionidae of the Order Coleoptera, is native to tropical and subtropical regions of Asia. It is one of the most devastating pests of mango crops, causing significant economic losses in mango production worldwide.
Since the larvae feed on the fruit, the quality and quantity of the harvest are significantly reduced. To effectively manage this pest, it is important to understand its life cycle, its preferred habitats, and the best methods for controlling it. This article will provide an overview and discussion of the Mango Nut Weevil Pest in Mango crops, including its symptoms, identification techniques, and control.
Mango Nut Weevil Pest Management
Life Cycle of Mango Nut Weevil Pest in Mango Crop
The life cycle of the mango nut weevil pest has four stages. They are egg, grub, pupa, and adult. The adult weevils are active from May to September and can lay up to 300 eggs per female, which hatch in two to three weeks. The adults lay their eggs by making small cavities in the skin of the fruits and covering it again with a brownish exudate. The eggs will hatch into grubs within one week.
The grubs will feed on the seed kernel for up to three months, which is the primary damaging stage of the weevil; they undergo five instars, after which they pupate in the seed within the stone of the fruit and emerge as adults in another two weeks. The pupae are encased in a case made of waxy material and are dark brown. The female starts laying eggs within 3-4 days after mating, and the cycle starts all over again. The lifecycle is completed in 6-8 weeks.
Occurrence of Mango Nut Weevil Pest in Mango Crop
- Location of Mango Nut Weevil pest: This pest infests mango crops in India, Africa, China, Burma, Bangladesh, Sri Lanka, Thailand, Malaysia, Indonesia, the Philippines, Australia, Vietnam, and Hawaii.
- Host range: The mango nut weevil is a monophagous species that feed exclusively on mango fruits.
Factors Favoring the Population Increase of Mango Nut Weevil Pest in Mango Crop
- Pest adaptation – The mango nut weevil has adapted to the changing environmental conditions accompanying increasing global temperatures. It can survive in various climates and has become resistant to many insecticides.
- Lack of natural predators – The mango nut weevil has few natural predators, which allows the population to increase unchecked. Natural enemies, such as birds and insects alone, cannot control the population.
- Pest mobility – The mango nut weevil is an extremely mobile pest, capable of flying long distances for food. This mobility allows the pest to spread to new areas, increasing its population.
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Identification of Mango Nut Weevil Pest in Mango Crop
- Eggs: The eggs are cream to white and lay in solitary or clusters.
- Grub: The grubs are small and yellow with a dark head and are legless.
- Adults: The adult Mango Nut Weevil Pest is a small, dark-brown beetle with a long snout and a 2 – 3 mm wingspan.
Damage Symptoms of Mango Nut Weevil Pest in Mango Crop
- The cavity wound made by the adults results in a sap flow that hardens and protects the eggs.
- The grubs feed on the mesocarp and make zig-zag tunnels in the pulp.
- They bore into the cotyledons and consume the endosperm, causing the seed to become hollowed out and unviable.
- The adults feed on the mango tree’s leaves, flowers, and fruits, causing defoliation and premature fruit drop at the marble stage.
- Egg-laying wounds can be observed on marble-sized fruits.
Percentage of Yield Loss in Mango due to Mango Nut Weevil Pest
- In India, the percentage of yield loss due to mango nut weevil pests ranges from 60-70%. In the United States, the losses range between 30-40%. In Africa, it is between 20-40%. In Mexico, it ranges from 20-30%. In the Philippines, the losses are at 40-50%. In Thailand, it ranges between 50-60%.
- The Economic Threshold Level (ETL) for the mango nut weevil pest is set at 3-4 adults per tree.
Cultural Control of Mango Nut Weevil Pest in Mango Crop
- Crop rotation – This involves planting non-host crops between mango tree rows so that the weevils that would normally attack the mango trees have fewer opportunities to feed and lay eggs.
- Sanitation – Collect and destroy dead, diseased, or deformed leaves, fallen fruits, and other crop debris from the field to reduce the intensity of the pest.
- Resistant varieties – Some varieties of mango trees that are naturally resistant to the weevil can help to reduce the damage caused by the pest.
- Pruning – Removing damaged plant parts like branches and under-sized fruits on the trees can help improve the plants’ health.
- Traps – Traps such as sticky, pheromone and light traps can trap adult weevils and reduce their population.
Biological Control of Mango Nut Weevil Pest in Mango Crop
- Parasitoid wasps, Trichogramma chilonis, and Aenasius bambawalei lay their eggs inside the larvae of the mango nut weevil. When the larvae hatch, the wasp larvae feed on them and eventually kill them.
- The fungus, Beauveria bassiana effectively kills the larvae of the mango nut weevil, reducing the damage caused by the pest. The fungus is applied to the soil and foliage of mango trees.
Chemical Control of Mango Nut Weevil Pest in Mango Crop
- Spray Cypermethrin, Endosulfan, Chlorpyrifos, Carbaryl, Quinalphos, Malathion, Acephate, or Fenthion first during the marble-sized fruit stage and again after a 15-day interval to protect the fruits from damage.
- Spray systemic insecticides such as imidacloprid and thiamethoxam directly on the foliage.
- Spray at the base of the trunk during the non-flowering season to get effective control.
- Spray deltamethrin from six weeks after the fruit set.
- Wash the infested bark with kerosene which acts as a fumigant to drive the pest away from the trees.
Preventive Measures for Control of Mango Nut Weevil Pest in Mango Crop
- Pruning should be done in late winter or early spring before the adult weevils emerge from the ground. The pruned parts should be destroyed to prevent the weevils from re-infesting the tree.
- Proper irrigation and soil management help improve the soil’s health and make it less hospitable for the pest.
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Conclusion
The mango nut weevil pest is a major issue for farmers, as it can cause significant crop loss. To reduce the impact of this pest, farmers should use integrated pest management strategies, such as crop rotation, proper sanitation, host plant resistance, and chemical control. By implementing these practices, farmers can reduce the impact of the pest and ensure a healthy mango crop.
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