Large Grain Borer
It is a pest that destroys stored maize, yam, sorghum, triticale and wheat and dried cassava. Both the adult borer and larvae feed internally on maize grains and infestation can even start in the field.
The adults and larvae can cause damage of up to 30% after 3-6months.
Image courtesy pioneer
- The eggs are normally white to yellow with no surface features. They normally have a broad ovoid shape.
- The larva is white, fleshy and has a sparse covering of hairs. The legs are short with a small head. The body is parallel sided and C-shaped.
- The adult beetle is normally 3-4.5mm long, dark brown with a body that looks like a flattened tube, with the end appearing like it has been cut straight. The body surface is pitted and has small wart-like outgrowths.
- The head is curved under the thorax so that the head can’t be seen from above.
- The antennae has 10segments (7-segment stem and 3-segment club)
- The difference with the lesser grain borer is that it is about 2-3mm long, dark red-brown with a body that is more rounded at the end and narrower.
- The difference with the maize weevil is that it is more rounded than the borer with its mouthparts beak like and antennae elbowed.
Its life cycle
- Female large grain borers make small egg laying chamber at right angles to the main tunnels. The eggs are then laid in batches of 20 and covered with finely chewed maize dust.
- The larvae hatch after 3days and live in the maize dust produced by the adult’s feeding activity.
- The last instar larva of the insect constructs a pupal case from frass stuck together with a larval secretion, either within the grain or in surrounding dust.
- Development of the larvae through the adult stage under the optimum conditions takes about 27days. They then disperse over short distances through flight. Females live for up to 61days than males 45 days.
Damage: They produce neat round holes when they eat into maize grains and the tunnel from grain to grain producing large quantities of maize dust. Damaged grains can be identified easily as they are normally covered by a layer of this dust.
Image courtesy wikipedia
Cultural control practices
- It can be reduced through good store hygiene
- Cleaning the store before harvest
- Removing and burning infested residues
- Immersing grain sacks in boiling water
- Removing wood from stores
- Fumigating the store to eliminate residual infestation
- Selection of only uninfected material for storage
- Harvesting the maize as soon as it reaches maturity
- The use of resistant cultivars
- The maize stock should be sold as soon as harvest to prevent being affected.
Physical control: Removal of adult insects from the grain by sieving can reduce populations, though requires much labor.
Inert dusts such as ash and clay can also help reduce insect numbers..
Biological control: This is majorly a predatory beetle (Teretrius nigrescens) that only eats LGB and controls larger grain borer.
Low-oxygen and carbon dioxide enriched atmospheres are important in controlling stored product pests
Freezing for several days, then heating for 24hours has proved to be an effective method.