The mango seed weevil, known by alternative names such as Mango nut weevil or Mango stone weevil, holds significant importance as a prevalent pest in the majority of mango-growing areas.

Life Cycle

The female mango seed weevil lays its eggs individually in small hollows it creates in the skin of young fruits. Afterward, the female makes a small crescent-shaped incision in the fruit, typically near the back end of the eggs. This incision causes sap to flow, which eventually hardens and forms a protective coating over the eggs. Multiple eggs may be laid in a single fruit, and they hatch within a period of 5-7 days. The newly hatched larvae then tunnel through the flesh of the fruit until they reach the seed, where they feed until they enter the pupal stage. Generally, the larval development occurs within the maturing seed, although occasionally it may take place within the flesh of the fruit. Pupation, which lasts approximately 7 days, occurs within the seed inside the stone of the fruit.

The entire life cycle of the mango seed weevil spans about 40-50 days, and only one generation is produced each year.

Identification

Eggs: The eggs of the mango seed weevil have an elliptical shape, measuring approximately 0.8 mm in length and 0.3 mm in width. When freshly laid, they have a creamy-white color.

Larvae: The larvae of the mango seed weevil are white grubs with a curved body, brown heads, and no legs. They are around 17 mm long. When newly hatched, the larvae are slender, elongated, and about 1 mm in length.

Pupae: The pupae of the mango seed weevil are initially whitish but gradually change to a very pale red color just before the emergence of the adult weevils. They measure approximately 8 mm in length and 7 mm in width.

Adults: The adult mango seed weevils are compact weevils, approximately 8 mm long. They have a black color and are covered with black, greyish, or yellowish scales. The adults are typically active at dusk, capable of flying, and exhibit a defense mechanism of feigning death when touched or disturbed.

During the flowering period, the adult weevils move up into the tree canopy to feed on new growth and engage in mating. The females start laying eggs around 3-4 days after mating, typically when the fruit reaches the size of a marble.

Adult weevils can live for up to two years.

Feeding & Damage

The destructive stage of the mango seed weevil is the larva, which penetrates the fruit by burrowing through the flesh and feeding on the seeds until it undergoes pupation. This feeding activity leads to the destruction of the seeds.

When the infestation occurs during the early stages of fruit development, it results in premature fruit drop.

In later stages of infestation, detecting fruit damage becomes challenging as there are no visible external signs, except for a subtle scar from egg-laying. The feeding activity within the seed remains unnoticed.

Infested fruits exhibit internal decay on the outer surface of the seed. The seeds develop holes, and the cotyledons become black and decompose, hindering successful germination.

Upon reaching maturity, the adult weevil emerges by tunneling through the flesh, leaving a hole in the fruit’s skin. In late-maturing mango varieties, this tunneling causes post-harvest damage to the pulp, resulting in an unsuitable product for the market. Additionally, the hole serves as an entry point for secondary fungal infections.

Adult weevils consume mango leaves, tender shoots, or flower buds as part of their diet.

Management & Control

Given the significant losses caused by mango seed weevil infestations, it is crucial to implement effective control and management measures for this insect pest. Several methods can be utilized, including the following:

Chemical Control

Chemical control entails the utilization of insecticides to eliminate the mango seed weevil pest. The selection of the appropriate chemical relies on various factors, including its Pre Harvest Interval (PHI) and efficacy, among others.

The following insecticides are recommended for combatting mango seed weevil:

  • LEXUS 247SC: 8ml/20l
  • EMERALD 200SL: 10ml/20l
  • LOYALTY 700WDG: 5g/20l
  • KINGCODE ELITE 50EC: 10ml/20l
  • BACIGUARD 16WDG: 15g/20l
  • PENTAGON 50EC: 10ml/20l
  • EPITOME ELITE 500SP: 10g/20l

Note:

  • It is advisable to mix the insecticide with INTEGRA at a rate of 3ml/20l to enhance its efficacy. INTEGRA functions as a spreader, wetter, penetrant, and sticker.
  • Timely application of insecticides is crucial for achieving effective control.

Non-chemical Control

Non-chemical practices encompass various methods, which include:

  • Orchard quarantine: It is crucial to prevent the movement of fruits from areas known to have mango seed weevil infestations to regions where young orchards, which are free from the weevil, have been established.
  • Sticky bands: These are applied to the upper part of tree trunks during the flowering period. They help reduce the migration of weevils to branches for egg-laying.
  • Maintaining good orchard sanitation: Proper sanitation practices in the orchard, such as removing fallen fruits and debris, can significantly reduce the population of mango seed weevils.
  • Planting resistant varieties: Opting for mango varieties that exhibit resistance to mango seed weevils can be an effective strategy in managing the pest.
  • Rotations and intercropping: Implementing crop rotations and intercropping with non-host trees like papaya, citrus, etc., can help decrease the population of the pest.
  • Proper weed control: Maintaining weed-free orchards aids in reducing the favorable habitat and food sources for mango seed weevils.

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