S. TRAORE, I. OUEDRAOGO & B.H. BAMA

The preservation of cereals in general, and maize in particular has always been of major concern both to big warehouses and producers. Modern protection methods requiring special installations are used in the big stores spread all over the country. However, traditional methods still prevail among producers in spite of the sensitisation campaign. The insects with the highest presence in maize stocks are still Sitophilus zeamais Motschulsky, Rhizopertha dominica F., Tribolium castaneum Herbst, Tribolium confusum du Val, etc.

The presence of the Larger Grain Borer, Prostephanus truncatus (Horn) in Burkina Faso was discovered in 1991 by Bosque-Pérez et al. (1991) from surveys carried out through the use of pheromone traps.

The original home of the Larger Grain Borer is maize stored in grains from North and Central America (Chittenden, 1895, Back & Cotton, 1922, all quoted in Haubruge & Gaspar, 1990). Accidentally introduced into the African continent, this food crop stock pest was first discovered in Tanzania in 1981 (Dunstan & Magazini, 1981). In West Africa, the beetle was first discovered in Togo in 1984 (Harnisch & Krall, 1984). From the southern part of the country, this pest moved towards the North, and this led to the researches carried out in Burkina Faso.

Prostephanus truncatus is one of the most dangerous stock pests and a high level of loss is recorded as a result of its activities (Haubruge & Gaspar, 1990). Golob and Hodges (1982) estimate the weight loss between 15% and 35% of maize after six to eight months in storage. This study highlights the presence of the pest in the different regions of the country and its increasing presence in warehouses where it may cause great damage.

Pheromone traps with binary pheromones containing active ingredients of "Trunc Call I and II" were used on the experimental field stations of Kamboinsé, Farako-Ba and Banfora. The traps were set once a month between November 1995 and February 1996. The surveys were carried out on the same sites mentioned above. It involved the collection of 10 samples of 1 kg from each warehouse. One additional kg was collected from 10 previously selected sellers. The samples were collected once a month between November 1995 and February 1996. After collection, the traps and maize samples were taken to the laboratory for sorting. The different insects found were labelled according to their species and the region in which they were found.

The results show that S. zeamais had the highest presence in all the three areas. This was followed by R. dominica, and finally by P. truncatus, whose population were negligible. The highest level was captured from stores in the same areas. The pheromone traps set in the trapping areas and sites between November 1995 and February 1996 in Ouagadougou captured some insects. In total three specimens of P. truncatus were caught, two on the experimental station at Kamboinsé, and one on the Banfora market (Tab. 1). No captures were made in the other sites.

The number of the other pests varied according to the trap sites. S. zeamais and R. dominica were the major insects discovered. The market trappings captured three S. zeamais at Ouagadougou, and five at Banfora. None was captured in Bobo-Dioulasso. The number of insects captured in stores was higher - 32 S. zeamais were recorded in Ouagadougou, compared to 13 in Bobo-Dioulasso and 26 in Banfora, respectively (Tab. 2). The presence of the R. dominica was relatively low in the stores, with six in Ouagadougou, and two Bobo-Dioulasso and Banfora, respectively. On the research stations, only S. zeamais was identified, with 12 specimens recorded in Ouagadougou and four in Bobo-Dioulasso, respectively.

Tab. 2.

Store pests discovered in different sites of Burkina Faso (samples of 10 kg were taken at each site and locality once a month; observation period November 1995 until February 1996; Pt = P. truncatus, Sz = S. zeamais and Rd = R. dominica).)

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	Localities
	Ouagadougou	Bobo-Dioulasso	Banfora

Sites

Pt

Sz

Rd

Pt

Sz

Rd

Pt

Sz

Rd

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Markets Warehouses Research stations

0 0 0

977 1875 678

128 617 58

0 0 0

122 375 30

77 42 12

0 0 0

1022 2386 351

158 822 25

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The results of the store samples reveal the absence of the Larger Grain Borer. In contrast, the presence of S. zeamais and R. dominica was very high in all the sites surveyed. The results of table 2 also show a higher infestation of S. zeamais and R. dominica in the warehouses than on the markets and research stations. We did not come across any P. truncatus during our research, neither in the traps nor in the maize samples. Maize is more infested in the Banfora stores, followed by Ouagadougou.

Overview

The results of these studies confirm the presence of P. truncatus in Burkina Faso. Its presence had already been documented by Bosque-Pérez et al. (1991). However, the Bobo-Dioulasso and Banfora localities were not considered by the authors. Since then the Larger Grain Borer has reached all the ecological zones of the country. The very low number of insects captured shows that the population of the Larger Grain Borer is not high in Burkina Faso. This stock pest was discovered since 1991. This data confirms an almost zero growth rate and therefore hardly any effect on stock at the moment. This low growth rate can be attributed to the rapid renewal of maize stock. The massive presence of some traditional pests like S. zeamais and R. dominica was also noted. These primary pests cause most of the damage recorded on stock maize.

The absence of P. truncatus in the different warehouses confirms the remarks of Cave and Wright (1989), which say that this insect is generally absent in the warehouses of Central America. The high presence of other pests like S. zeamais and R. dominica may also explain the absence of P. truncatus. Biliwa and Richter (1990) report in their studies on populations of P. truncatus and S. zeamais that the predominant species at the beginning of storage or the one that grows more rapidly reduces the activities of the other species considerably.

Conclusion

The presence of the Larger Grain Borer in Burkina Faso was confirmed by this study. Moreover, this pest is present in all the ecological zones of the country. Nevertheless, its does not seem to play a major part in the damages recorded. Traditional pests like S. zeamais, R. dominica etc. are responsible for the larger part of the damage noted. Studies on P. truncatus should be continued in order to follow up on its future progress, since maize production is expected to increase considerably in view of the pace at which cultivation technology is currently being improved and cultivation area increased.

These studies did not take into consideration farmers' situation where the greatest damage is often recorded. A survey would facilitate the updating of the current activities of the Larger Grain Borer in Burkina Faso.

 

References

Biliwa, A. & Richter, J., 1990.
	Efficacité d’insecticides binaires en poudre sur du maïs égréné stocké en sacs, pp. 1577- 1585. In Fleurat-Lessard, F. & Ducom, P. [eds.]: Proceedings 5th International Working Conference on Stored -Product Protection. Bordeaux, France.
Bosque-Pérez, N.A., Traore, S., Markham, R.H. & Fajemisin, J.M., 1991.
	Occurrence of larger grain borer Prostephanus truncatus in Burkina Faso. FAO Plant Protection Bulletin 39: 182-183.
Cave R.D. & Wright de Malo, V., 1987.
	Perspectives de recherche sur le grand capucin du maïs en Amérique centrale, p. 5. In Markham, R.H. & Herren, H.R. [eds.]: Comptes Rendus d’une Réunion de Coordination IITA/FAO tenue les 2 et 3 Juin 1989 à Cotonou, Bénin.
Dunstan, W.R. & Magazini, I.A., 1981.
	Outbreaks and new records: Tanzania. The larger grain Borer on stored products. FAO Plant Protection Bulletin 29: 80-81.
Golob, P. & Hodges, R.J., 1982.
	Study of an outbreak of Prostephanus truncatus in Tanzania. Report G164 of the Tropical Products Institute, Chatham, UK.

Harnisch, R. & Krall, S., 1984.
	Further distribution of the larger grain borer in Africa. FAO Plant Protection Bulletin 32: 113-114.
Haubruge, E. & Gaspar, C., 1990.
	Détermination en laboratoire des zones maïs égrené stocké en sacs, pp. 921-935. In Fleurat-Lessard, F. & Ducom, P. [eds.]: Proceedings 5th International Working Conference on Stored -Product Protection. Bordeaux, France.