Insect Pests of Fruit, Plantation, Medicinal & Aromatic Crops (2+1)

6. Mango nut weevil

6. Mango nut weevil - Sternochetus mangiferae Fab. (Curculionidae: Coleoptera)

Damage

• The grub tunnel in a zig - zag manner through the pulp endocarp and the seed coat and they finally reach the cotyledons.
• As the fruit develops the tunnel get closed.
• The grub feeds on the cotyledons and destroy them.
• The adults who emerge from the pupae also feed on the developing seed and this may hasten the maturity of infested fruits.


Bionomics

• The adult weevil is stoutly built, 6 mm long, dark brown in colour.
• It lays eggs singly on the marble sized fruits by scooping out the surface tissue and cover over with a transparent secretion.
• The ovipositon puncture heals leaving minute spot. On a single fruit up to 15 eggs may be laid in a day.
• The egg period is 7 days.
• The newly hatched out grub is creamy, yellow apodous tunnel the fruit pulp and enter into cotyledons.
• The larval period is 20-30 days. It undergoes five larval instars and pupate inside the nut along the concave side.
• The pupal period is 7 days. The total life cycle occupies 40-50 days.
• The adult often remain inside the nut until they are thrown away after consumption of the pulp.
• The weevil hides in crevices of the tree trunk as they have longevity of 10 months.
Management

• Follow prophylactic measures in Neelum and Bangalora varieties as these varieties are susceptible.
• Collect and destroy the fallen fruits, which contain 85 % of the weevil
• Spray emamectin benzoate 1 ml / litre during marble stage and second spray at 15 days after the first spray.
• Take up insecticides spray directing towards the base of the trunks during the non-flowering season.
• Tieing red ant colonies in mango orchards help to reduce the damage of nut weevil remarkably.