Scientific Name: Prostephanus truncatus (Larger grain borer)

Common Names; English: Larger grain borer, greater grain borer 

Synonyms

Dinoderus truncatus; Stephanopachys truncatus 

Taxonomic Position

Phylum: Arthropoda

Class: Hexapoda (Insecta)

Order: Coleoptera

Family: Bostrichidae

Geographical distribution

Africa - Benin, Burkina Faso, Burundi, Ghana, Guinea, Kenya, Malawi, Mozambique, Namibia, Niger, Nigeria, Rwanda, Senegal, South Africa, Tanzania, Togo, Zambia

North America - Canada, -Manitoba, Mexico, USA-Arizona, California, District of Columbia-Montana, New Jersey, New York, Oklahoma, Texas

Central America and Caribbean - Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama

South America -Brazil-Minas Gerais, Colombia, Peru

Europe -Italy-Sicily

Host Range

LGB is a serious pest of stored maize and dried cassava roots, but will also attack maize in the field just before harvest. Minor hosts include yam, sorghum, triticale and wheat. LGB is also present on a number of wild hosts and can infest wooden grain storage structures.

Pest Destructive Stage

Primary pest

Both the adults and larvae damage the grain though only the adults produce tunnels. Damage can be severe with weight losses of sometimes around 30% after 3-6 months storage.

Damage Symptoms

Adult LGB produce neat round holes where they eat into the maize grains. They tunnel from grain to grain producing large quantities of maize dust. Damaged grains can be identified as they are usually covered by a layer of this dust. Weight loss due to flour production outweighs losses due to direct consumption.

Identification features

Eggs 

White to yellow in color, with no surface features and broad ovoid (ellipsoidal) in shape

 Larva 

The LGB larva is white, fleshy and has a sparse covering of hairs. It has a parallel-sided C-shaped body. The legs are short and the head is small.

 Adult

• The adult beetle is 3 - 4.5 mm long, dark brown with a body that looks like a flattened tube, the end of which appears to have been cut straight. 
• The body surface is pitted and has many small wart-like outgrowths (tubercles). 
• The head is curved under the thorax so that the back of the head cannot be seen from above.
• The antennae have 10 segments, made up of a 7-segment 'stem' and a 3-segment 'club'.  

Adult – dorsal view	Antennae	Head front

Similar Species

It is possible to confuse the LGB with other storage insect pests such as the lesser grain borer (Rhyzopertha dominica) and the maize weevil (Sitophilus zeamais). The lesser grain borer is about 2-3 mm long, dark red-brown with a body that is more rounded at the end and narrower than that of the LGB. The end of the body of the maize weevil is also more rounded that of the LGB and its mouthparts are 'beak-like' and antennae elbowed.

Life Cycle

• Adult LGB eat into maize grains; females make small egg laying chambers at right angles to the main tunnels.
• Eggs are laid in batches of 20 and covered with finely chewed maize dust.
• The larvae hatch after about 3 days at 27°C and live on the maize dust produced by the adult's feeding activity.
• The last instar larva of LGB constructs a pupal case from frass stuck together with a larval secretion, either within the grain or in the surrounding dust.
• Development of the larva through to the adult stage on a maize diet and under the optimum conditions of 32°C and 80% humidity takes about 27 days.
• Adults disperse over short distances through flight. Females live longer (61 days) than males (45 days).

Detection methods

As the LGB larvae develop inside the grain it is difficult to detect the pest by visual inspection unless its numbers are very high. Adults can be attracted to flight traps baited with aggregation pheromones. LGB respond poorly to pitfall and probe traps inserted into grain bulks.