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GRAIN BORER

The larger grain borer was accidentally introduced from Central America into Tanzania in the late 1970s, and spread to other countries in the region. In West Africa it was first found in Togo in the early 1908s. It has now spread to many African countries becoming the most destructive pest of stored maize in both West and East Africa. Up to date it has been reported in Benin, Burkina Faso, Burundi, Ghana, Guinea Conakry, Kenya, Malawi, Mozambique, Namibia, Niger, Nigeria, Rwanda, South Africa, Tanzania, Togo, Uganda and Zambia. In some of these countries it has become a serious pest of stored maize and dried cassava.

Damage

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The larger grain borer is a serious pest of stored maize and dried cassava roots, and will attack maize on the cob, both before and after harvest. Adults bore into the cassava or maize husks, cobs or grain, making neat round holes and tunnelling extensively producing large quantities of grain dust as they tunnel. The adults prefer grain on cobs to shelled grain, thus damage on unshelled maize is greater than on loose, shelled maize.

When infesting stored maize cobs with husk intact, the adults frequently begin their attack by boring into the maize cob cores, and eventually gain access to the grain at the apex of the cob by crawling between the cob and husk. They may also bore directly through the husk. They cause considerable losses in stored maize; weight losses as high as 35% have been observed after only 3 to 6 months storage in East Africa. Losses in dry cassava can be very high too; the dried roots may be readily reduced to dust by boring adults. Average losses of 19% have been recorded after 6 months storage and as much as 30% in some cases.


The larger grain borer is spread over longer distances almost entirely through the import and export of infested grain. Local dispersal is through the local movement of infested maize and dried cassava and by flight activity of the adult beetles.

Although the larger grain borer develops best at high temperature and relatively high humidity, it tolerates dry conditions, and may develop in grain at low moisture in contrast to many other storage pests, which are unable to increase in number under low moisture conditions. For this reason, infestations of the larger grain borer usually found together with other storage pests, is the predominant storage pest under dry conditions.

Attack by the larger grain borer is sporadic. Pest incidence may be low for several years and then suddenly increase in a "bad" year.

Symptoms
Adults tunnel through stored maize grain or other starchy products, such as dried cassava chips, creating large quantities of dust.

Host range
The larger grain borer is reported to breed only in maize and cassava. The adults can, however, live in and damage many stored products such as bulrush millet sorghum, yam, and wheat, as well as structural wood and wooden utensils.

Adults also bore into a wide range of foodstuffs and other materials such as bamboo, gourds, plastic and soap. In heavy infestations, wooden storage structures may be become damaged and act as reservoirs of infestation from which the new harvest may be attacked. The larger grain borer also occurs in the natural environment, it is able to breed on dead, dry wood of a range of trees, as well as dried stems of cassava and maize plants. Studies of this pest using pheromone traps showed that it was widespread in the natural vegetation in the Tsavo National Park, Kenya (Nang'ayo et al., 1993, 2002, Nansen et al., 2004).

THE LESSER GRAIN BORER

Identification
The Lesser Grain Borer is a small black or dark brown beetle. The body is slender and cylindrical. The head issad hidden under the prothorax which is finely textured with bumps and dimples. The elytra (hardened front wings forming the shell) have rows of pits along their length. The antennae have 10 segments with the last 3 forming a club shape. The larvae are white, stout and c-shaped.

Size
adults are 2mm - 3mm long

Food
The lesser grain borer is a serious pest of stored grain and cereal products. The adults and larvae bore into grain seeds and eat the kernel leaving a hollow husk. They are mainly a pest in stored wheat and corn, but can also infest nuts, beans, dried fruit, peanuts and various other types of stored food.

Breeding
Adult females lay their eggs singly or in groups of up to thirty eggs. The eggs are laid on the outside of a grain or in the powdered "flour" from damaged seeds. The lifecycle from egg to adult takes about 60 days, but may take as few as 30 days in warm conditions. The larva pupates inside as hollow seed or in the accumulated powdered flour from the infestation.

Lesser grain borers mainly attack wheat, corn, rice and millet. Both the larvae and adults are primary pests. They bore irregularly shaped holes into whole, undamaged kernels and the larvae, immature stages, may develop inside the grain. Larval and adult feeding in and on grain kernels may leave only dust and thin brown shells. A sweet, musty odor is often associated with infestations of this insect.

The adults have cylindrical bodies and numerous small pits on the wing covers. The head is directed downward and covered by the prothorax so that it is not visible when the insect is viewed from above.The female deposits her eggs in clusters of 2 to about 30 on kernels. Most of the newly-hatched larvae chew into kernels and complete their entire development there. However, the larvae can feed on fines or can develop as free-living insects in the grain. There are four larval stages. Development from egg to adult requires about 25 days under ideal conditions.

It is the Main insect causing significant damage to all cereals, including maize. The control of insects for maize must start before the harvest and not only when they are detected in storage. We are ready to advise you on the best control strategies.

We have tremendous experience in this field. We also use disinfection using various pesticides. We are capable of contolling both the large and the lesser grain borers using various cultural, chemical and biological methods.

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