Insect Pests – Pseudostem Weevil / Borer

Insect Pests – Pseudostem Weevil / Borer:

Symptoms:

The Pseudostem weevil (Odoiporus longicollis) are normally black coloured ones but red coloured variants are also found in some areas. The pest breeds and become more active during summer and monsoon seasons.

Early symptoms of infestation are the presence of small pin-head sized holes on the pseudostem, fibrous extrusions from bases of the leaf petioles and exudation of a gummy substance from the holes of the pseudostem.

The weevil larvae are fleshy and yellowish white. Larva bores hole through the pseudostem and thrives inside. This results in exudation of plant sap followed by dropping of the faecal matter. As the central core is destroyed due to the boring of the larvae, upward movement of the nutrient is hampered which ultimately results in poor growth and development of the plants.

If the larva tunnels pseudostem during advanced pre-flowering stage, the ascending flower bud and peduncles are destroyed resulting in non emergence of the flower bud which decays inside the pseudostem. This leads to choked throat appearance of bunch and breaking of Pseudostem.

During advanced stages of infestation, we can observe by splitting the stem, the pests' extensive tunneling both in the leaf sheath and in the rhizome. Rotting occurs due to secondary infection of other pathogens and foul odour is emitted. When the rhizome and peduncle are tunnelled after flowering, the fruits do not develop properly, exhibiting a dehydrated condition with premature ripening of the bunch.

Pseudostem weevil affected plant with immature bunch

Pseudostem weevils / grubs

Pseudostem weevil attack - Bore hole on Banana

 Control:  

1. Keep the plantation clean.  
2. Remove trashes and burn the refuse. 
3. Do not dump infected plant into manure pit. 
4. Uproot infected trees, chop into pieces and burn. 
5. You can be rest assured of infection free planting material if you go for ‘Tissue culture plants. If you opt for suckers, then avoid planting of borer infested suckers. To make sure that you have clean suckers, the roots should be trimmed and pared-off all tissues on the surface to make it free of any infestations and dip the pared corm in a solution containing 0.5% Monocrotophos or 2.5 ml in 1 litre solution of Trizophos for 30 minutes. Alternatively application of 40g of Carbofuran in the soil at planting can also be followed. 
6. Do not plant susceptible varieties in the endemic areas such as Nendran, Mondan, Ney poovan etc. 
7. Dilute Monocrotophos 150 ml in  350 ml of water and inject 4 ml in the pseudostem about 2 feet higher from the ground (preferably below bore hole) using Pseudostem injector in a 45 degree slanting angle. For more details click this link: A novel method for effective control of Pseudostem weevil using Pseudostem Injector. 
8. Rake the soil around the pseudostem and apply 0.1% Metasystox or 0.05% Quinalphos or 0.03% Chlorpyriphos or 0.2% Carbaryl followed by light irrigation, at 15 days interval.  
9. Method to trap the weevil with spilt pseudostem: The freshly cut pseudostem is a good breeding place for weevils. So, after the bunch has been harvested, cut the pseudostem close to the ground then cut it into small pieces in lengths of up to 60 cm, split each along its length and place them in the soil in the way that the cut portion faces the ground. These cut pieces (split traps) attract adult female weevils to feed and lay their eggs. As soon as the larvae emerge, these pieces become dry and eventually the larvae die because of dehydration. This split trap method to trap the weevil is just to monitor the extent of infection in the field and control measures have to be taken up immediately.
10. The open cut side of the above pseudostem cut pieces about 30 to 40 numbers (split traps) can be sprayed with 0.5% solution of Beauveria bassiana or  Metarhizium anisopliae,  both are entomopathogenic bio control agents before placing them face down on the soil. The weevil gets infected by the fungal conidia (spores) when it enters the pseudostem trap. It is enough for the conidia of the fungus to come in to contact with the body of the weevil or ingested where it grow and colonize the host body. Then they germinate and the hyphae that emerge penetrate the cuticle of the insect host. After extensive invasion of the host body, the Destruxins produced by the fungus eventually weaken and kill the insects within 72 hours.
11. Use Pheromone traps (2 traps/acre) and destroy the collected weevils. 

A Pseudostem Injector and a Pseudostem cut piece for weevil trap

Regards,
A.Vishnu Sankar