A. TOKO & A.H. BOKONON-GANTA

Significant losses are registered in maize harvest because of pests. The most destructive of these pests is the Larger Grain Borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), which was accidentally introduced from America. The SPV has recommended different methods including binary pesticides with organo-phosphate and pyrethroid bases for use on the maize grains. The main problem with this method of control is the fact that farmers have to shell the maize. Furthermore the risks linked to farmers' use of non-recommended products to treat the maize husks led the SPV to experiment on preservation with less toxic insecticides but this did not yield any positive result. Consequently, following the impressive results being recorded in the area of biological control of the pests, the SVP recommended and extended the integrated control approach based mainly on biological control. This paper is an up-date of the achievements made in the control of P. truncatus, and the prospects of an integrated and sustainable management of the pest in Benin.

Considerable loss is recorded during the storage of food crop harvest due to the activities of pests. Most post-harvest pests are transported from the farm during harvest to the storage space. It is therefore necessary to protect harvest against the loss occasioned by these pests through the implementation of strategies incorporating different control measures in order to ensure sustainable protection of harvested crops.

The Insect Pest Complex

The major stock pests in Benin belong to the Coleoptera and Lepidoptera orders. These pests infest staple food crops and make them unsuitable for consumption. Among insects in the Coleoptera order that are harmful to maize are the weevil, Sitophilus zeamais, the grain borer, Rhizopertha dominica, the Tribolium spp., the toothed butterfly, Oryzaephilus surinamensis, the red cucujid, Cryptolestes ferrugineus. The major Lepidoptera (moths) are the meal moths, Corcyra cephalonica, the corn-moth, Sitotroga cerealella, Cadra cautela, and Plodia interpunctella which may cause considerable damage to maize grains and maize flour in storage. The larger grain borer, P. truncatus, accidentally introduced from America and Mexico has, in the last ten years, added to the number of these pests. P. truncatus is different from all the other pests because it is more prevalent in maize, other stocked products and even construction materials. Maize stock infestation by P. truncatus translates into large losses for small producers.

To ensure good preservation of stock, the use of insecticides, especially the Actellic PP (2% Pirimiphos Methyl) was recommended for most of the pests, and where P. truncatus infestation is suspected, the Super Actellic PP (Pirimiphos methyl & Permethrin) and the Sofagrain PP (Deltamethrin 0.5% & 1.5% Pirimiphos methyl) at the rate of 50g/100kg of grain was recommended for the treatment of maize grains.

The results achieved in the protection of stock vary considerably among farmers who are in the habit of using pesticides. In Benin, the damage caused by the Larger Grain Borer on the stock of small farmers who store in husks in traditional granaries is much more severe than that of large-scale producers who have better storage spaces, and who adopt SPV recommendations. The surveys carried out to evaluate the effectiveness of this method revealed that farmers usually do not have the time to de-husk the maize before storage and continue to store their stocks in husks. The application of dust powders offers only a limited surface protection to the stocked products. The product does not reach the insects inside the husked cobs before the application of the insecticide, thereby limiting the effectiveness of this control measure. The results obtained in the use of the above pesticides in the treatment of maize in husks is therefore unfortunately rather unimpressive. Concerned with protecting their stock at all cost, and at least cost, farmers persist in the use of different un-recommended products, especially those meant for the treatment of cotton crops and others obtained from doubtful sources.

In view of the situation described above, and the farmers' desire for a product for the treatment of maize in husks, the SPV focused on the use of chemical products available in the immediate environment of the farmers which constitute less risks than cotton pesticides. For this purpose, a test protection method against stocked husked maize was designed and installed in the Ouémé province, South East of the country.

Aware of the important role of the biological control in the implementation of the integrated control approach in the sustainable management of grain store pests, and with due consideration to the performance of one of its natural enemies, T. nigrescens, and its release whose result was encouraging in some countries in the sub-region such as Togo and Ghana, SPV considered it important to set up and run a unit to rear the natural predator of P. truncatus. This is what justified the training on the techniques of rearing T. nigrescens, the natural predator of the Larger Grain Borer. The purpose of this training is to boost the technical skills of the SPV in the implementation and methodology for rearing the natural enemy.

This five-day training took place at IITA-Benin with the financial support of the GTZ Supra Regional Project. It facilitated the training of an SPV technician on the different stages of rearing, especially the installation and maintenance of the pure culture of the pest, and mass breeding of the beneficial insect.

Since the introduction of the pest, and after several years of control measures, it has become obvious that the control of the Larger Grain Borer is better done collectively than individually. The collective control is accomplished with the co-operation of the different Departments, institutions and organisations involved in stock protection, and farmers who are the major beneficiaries of the methods to be applied. This explains why, in addition to the control measures themselves, the SPV has embarked on other activities including the sensitisation of populations on the real problem posed by the pest, in order to launch an effective and sustainable control of the pest.

Generally, the objectives of the different activities are:

In order to achieve these objectives, the following major actions have been planned for:

Conclusion

The concern of the SPV is to further entrench the actions carried out on the control of P. truncatus, and to implement them within an integrated pest management system with a view to ensuring an effective and sustainable control of the pest.