Mango seed weevil (Sternochetus mangiferae) is one of the most important mango pest and is widespread in most mango-growing regions.
It is also called Mango nut weevil or Mango stone weevil.
Life Cycle
Eggs are laid singly in small cavities made by the female in the skin of young fruits .The female then cuts a very small crescent-shaped area in the fruit, usually near the back end of the eggs. This wound creates a sap flow, which hardens and covers the eggs with a protective coating. Several eggs may be laid in each fruit. They hatch within 5-7 days. The larva burrows through the flesh of the fruit into the seed where they feed until pupation. The development of the larva is usually completed within the maturing seed, but also very occasionally within the flesh. Pupation takes place in the seed within the stone of the fruit, and this takes about 7 days.
The life cycle is completed within 40-50 days and only one generation is produced each year
Identification
Eggs– these are elliptical, about 0.8 mm long and 0.3 mm wide and are creamy-white in colour when freshly laid.
Larvae– they are white grubs with a curved body, brown heads, legless and about 17mm long. Newly hatched ones are extremely slender, elongated and about 1 mm long.
Pupae– these are whitish when newly formed, but change to a very pale red colour just before the emergence of the adults. They are about 8 mm long and 7 mm wide.
Adults– these are weevils with a compact body and about 8mm long. They are black, and covered with black, greyish or yellowish scales. Adults are usually active at dusk, can fly and pretend to be dead when touched or disturbed.
During flowering the adults move into the canopy of the tree to feed on new growth and to mate. Females start egg laying 3-4 days after mating, when the fruit is about marble-size.
Adults can live for two years.
Feeding & Damage
The larva, which is the damaging stage of the pest, enters the fruit burrowing through the flesh into the seeds where they feed until pupation thus destroying the seed.
Attack when the fruits are forming, i.e., at early fruit development stages, leads to premature fruit fall.
If attacked at a later stage, fruit infestation is very difficult to detect, since there are no external signs of infestation, except for an inconspicuous egg-laying scar, and consequent feeding activity in the seed remains undetected.
Infested fruits present internal rot on the outer surface of the stone. The stones develop holes and the cotyledons turn black and become a rotten mass. Damaged seeds hardly germinate
As the adult emerges, it tunnels through the flesh into the open, leaving a hole in the fruit skin. In late-maturing varieties, it causes post-harvest damage to the pulp as the tunnel turns hard making the fruit unmarketable. This hole also serves as an entry point for secondary fungal infection.
Adult weevils feed on mango leaves, tender shoots or flower buds.
Management & Control
Considering the losses attributed to infestations with mango seed weevil, it is of great necessity to control and/or manage this insect pest. A number of methods can be employed and these include the following;
Chemical control
This involves the use of insecticides to eradicate the pest. The choice of the chemical depends on several factors like its Pre Harvest Interval (PHI), effectiveness, among others.
The following insecticides are fit for use against 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
NB;
- Always mix the insecticide with INTEGRA 3ml/20l in order to improve on its efficacy. This is a spreader, wetter, penetrant and sticker.
- Timely application of insecticides is very important for effective control.
Non- chemical practices
They include;
- Orchard quarantine- fruits from areas known to have mango seed weevils should not be moved to areas where young orchards, free from seed weevil, have been cultivated.
- Sticky bands- these are applied at the upper end of tree trunks when the trees start flowering to help in reducing migration of weevils to branches for egg laying.
- Maintenance of good orchard Sanitation
- Planting resistant varieties
- Rotations and intercropping with non-host trees like papaya, citrus, etc. in order to reduce the pest’s population.
- Proper weed control
