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New data on distribution, research and control of the Larger Grain Borer

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Prostephanus truncatus (Horn), the Larger Grain Borer (LGB), and its control in Tanzania
Recent developments in Kenya on the ecology and control of Prostephanus truncatus
Evaluation de la répartition du Prostephanus truncatus (Horn) (Col.: Bostrichidae) par utilisation de pieges a pheromone sur le territoire du Togo
Distribution, recherche et controle du grand capucin du maïs Prostephanus truncatus (Horn) au Benin
Situation report on the Larger Grain Borer in Ghana
The integration of biological and chemical control components of an integrated pest management strategy for the Larger Grain Borer in Africa
Discussion - First session.

 

Prostephanus truncatus (Horn), the Larger Grain Borer (LGB), and its control in Tanzania

G.A. Mallya
MALD, Arusha, Tanzania

SUMMARY

The introduction and rapid spread of the Larger Grain Borer in Tanzania, where it has become a major pest of stored maize and dried cassava, is described. Presently the pest is found in 16 out of 20 regions on the Tanzanian mainland, and has been reported from approximately 3,000 out of a total of 9,000 villages, affecting between 1 and 1.5 million households. From Tanzania the pest has also spread into Kenya and Burundi.

Losses of up to 35% may occur in 5-6 months of maize storage if no proper control measures are taken. Such losses render the maize unfit for human consumption. Because of the high risk posed by this pest to the household food supply, but also the export market, a strategy has been developed for the containment and control of the Larger Grain Borer. Detailed information is provided on the range of activities which are being implemented to contain and control the pest.

INTRODUCTION

The LGB is endemic to Mesoamerica, where it is not of economic importance. In Tanzania, since its introduction in the late 1970's, LGB has become a major pest of stored maize and dried cassava, the two major staple foods.

Farmers from Tabora District in western Tanzania reported in 1980 the presence of an unknown pest destroying stored maize and dried cassava. It is assumed that the pest had been introduced into the country with maize imports. Locally it became known as "Scania", referring to the shape of the head, which was very distinctive compared to other important, traditional storage pests, and which resembled the cabin of that particular type of truck. Another name under which it became known was "Dumuzi", which is the noun of the verb "dumula" in the Kinyamwezi language, meaning to grind maize into flour, which is one of the characteristics of LBG in stored maize.

The Ministry of Agriculture and Livestock Development (MALD) conducted a number of surveys to determine the spread of the pest and samples were sent to the British Museum of Natural History in London for identification. The pest was identified as Prostephanus truncatus (Horn), officially confirming its presence in Africa.

Further surveys to establish the spread of the LGB, carried out by a UK team (Golob and Hodges, 1982) and MALD indicated that the pest was well established in Tabora Region and in some villages in Shinyanga and Mwanza Regions. Between 1980 and 1984 the beetle had spread into Kenya (Taveta). From Tabora, the beetle spread westward into Kigoma Region from where it has spread into Burundi.

Other surveys revealed the presence of the LGB in Morogoro Region. The surveys also indicated that the spread of LGB in Tanzania is mainly through movement of grain from infested areas of surplus to areas of deficit. Infested empty gunny bags brought into maize surplus areas, which until then had been non-infested, contributed also to the further spread of the pest.

Currently, the pest is found in 16 out of 20 Regions on the Tanzanian mainland (Map 1). Of a total of over 9,000 villages in Tanzania, the pest has been reported from approximately 3,000 villages, and it affects between 1 and 1.5 million households (Table 1).

EFFECTS OF LGB ON FOOD SUPPLY AND FOOD SECURITY

Losses in maize and cassava caused by LGB are much higher than those caused by indigenous pests, and are inflicted in a relatively short period of time. At household level, losses may be as high as 35% in 56 months of storage, and losses of up to 60% or more may occur over a 9-month storage period (Golob and Hodges, 1982; Hodges et al, 1983; Keil, 1988). Weight losses of this magnitude render maize unfit for human consumption and therefore can be considered as a total loss. Such losses are jeopardizing Tanzania's efforts to achieve self-sufficiency in food production. In view of this, the MALD in 1983 declared the LGB problem an emergency situation. If the pest was not effectively controlled, the need for famine relief could well be the result.

LGB AND THE MAIZE/CASSAVA EXPORT MARKET

The actual losses caused by LGB in terms of export market and price effects on farmers and the nation at large are not well documented. However, indications are there to suggest that such losses are quite substantial. Tanzania has a great potential for regular exportable surplus maize. During the 1980's difficulties have been experienced with maize shipments by the World Food Programme, the European Economic Community and commercial enterprises. In 1987-88 for example, 18,000 tons of surplus maize could not be exported to Malawi and Mozambique due to concern about possible LGB infestation. As a consequence, a loss of US$ 1.5 million as missed export opportunity was suffered. Cassava may face similar export problems.

In the absence of an external market, the domestic market has to absorb all maize and cassava produced in the country. In this situation the domestic supply will exceed domestic demand, and the clearing market price for these crops will tend to fall. This in turn may discourage the production of these crops, threatening food security.

In view of the threat posed by the LGB to food security and to the export market, the Government of Tanzania places a strong emphasis on the containment and control of this pest.

THE LGB CONTAINMENT AND CONTROL STRATEGY

During the last decade, the Plant Protection Division of the MALD, with assistance from initially the Overseas Development Natural Resources institute (ODNRI), U.K., and later the Food and Agriculture Organization (FAO), has been heavily involved in LGB containment and control activities. The long term objective of the programme is to develop and implement a pest management system for the control of the LGB and other storage pests. A strategy for containment and control of LGB at national level has been developed and implemented. This strategy consists of:

1) Creating awareness and intensive farmer training;
2) Setting up of a distribution and sales system of insecticides down to farm level;
3) Training of staff of the Plant Protection Division and others;
4) Only allowing movement of treated maize and/or fumigated cassava, especially from infested to non-infested areas, and disinfestation of empty gunny bags;
5) implementation of intensive control campaigns in isolated outbreak areas to reduce LGB infestation levels and/or possibly eradicate the LGB in those areas.

LGB CONTAINMENT AND CONTROL ACTIVITIES

In the efforts to contain and control the LGB, attention has been given to the Post-Harvest system as a whole. The following is an overview of the different activities which have been developed and are being implemented.

1) Training

i) Personnel of the Plant Protection Division have been trained in all aspects of LGB control;
ii) A start has been made with the training of warehouse personnel of the Cooperative Unions and other institutions.

Appropriate training strategies and methodologies have been developed for the different target groups. Emphasis is put on the "training of trainers". Candidates are selected from the different target groups and trained in order to create a core of trainers in Store Management, Produce inspection, Pest Control and Quality Control.

2) Extension

In close cooperation with the extension services an LGB awareness has been created within the farming community throughout the country and also at administrative levels. Hundreds of village seminars are being conducted every year throughout the country by village extension workers with support from Regional and District Staff of the Plant Protection Division. Extension material (posters, leaflets, etc.) have been developed. In this way intensive training on LGB control measures, including improved traditional storage structures, has been given to thousands of farmers every year.

3) Insecticides

A cocktail dust of permethrin (0.3%) and pirimiphos-methyl ( 1.6%), to be admixed with sufficiently dry and shelled maize, was developed for use at farm level. Fumigation is used for the treatment of large stocks of maize and cassava. The cocktail dust (Actellic Super Dust) effectively controls LGB and other storage pests. The cocktail dust was recommended after testing a range of insecticides for their effectiveness against LGB and other storage pests. This work was carried out by staff of the MALD and ODNRI (Mushi, 1984; Golob et al, 1985).

Since 1983 an approximate 400 - 500 tons of initially, permethrin (which is specifically active against LGB), and later of the cocktail dust, have been distributed.

4) The Dumuzi Law of 1986

The introduction of the Dumuzi Law of 1986 has made it possible to control the movement of maize and dried cassava, which is especially important with respect to the movement of maize from infested to non-infested areas.

5) Intensive Control Campaigns

The Dumuzi Law also facilitated the implementation of intensive control campaigns. The MALD has trained Mobile Pest Control Teams which are deployed for these LGB control campaigns. Preparations for these campaigns include seeking the collaboration of Government and Party officials, parastatal bodies (e.g. Primary Societies, Cooperative Unions, National Milling Corporation) and others. LGB Committees have been established at Regional, District and Village levels to mobilize the general public to participate in the campaigns. All farmers in the villages covered by the control campaigns are requested to shell their maize prior to the arrival of the Pest Control Team. Farmers are trained in store hygiene, participate in the disinfestation of storage structures, and are required to admix their shelled maize with the recommended insecticide. Demonstrations are given on the procedure to follow for the admixing (Gilman and Nyakunga, 1988). The LGB control operation is done from house to house with the assistance of 10-cell leaders. In isolated outbreak areas, such as Mbeya, Iringa and Ruvuma Regions, it has been possible to reduce the pest populations to below economic levels or control the outbreak completely through these campaigns.

CONSTRAINTS TO THE CONTAINMENT AND CONTROL OF LGB

The lack of availability of the recommended insecticide at the right place and at the right time has frequently hampered the implementation of LGB containment and control activities. The inadequate functioning of some of the Cooperative Unions, responsible for the distribution of the insecticide, has been a major problem. Steps are presently being taken by the MALD to ensure the availability of the insecticide to the farmer.

The recommendation to farmers to properly dry, shell and treat their maize, and the recommendation to use improved storage structures, implies that many farmers have to change their traditional practice of storing maize on the cob. In some areas this recommendation appears to be difficult to accept as it requires more labour and a change in current storage practices.

A summary of all the intensive campaigns carried out between February 1986 and February 1990 is presented in Table 2. A total of 373 villages in isolated outbreak areas have been covered so far. If this same approach were to be used in areas where LGB infestation is more widespread, it may take 20-25 years, at the current pace, to cover all of the approximately 3,000 villages which have been reported to be infested with LGB. Efforts are underway to improve the efficiency of the campaigns through better planning, using the recent compilation of available information on LGB spread. A plan of operation has been designed for an intensive control campaign in Morogoro Region which will cover some 356 villages, with approximately 150,000 households, over a period of about 2 1/2 months.

Difficulties have been encountered in implementing the Dumuzi Law. Shortages of the insecticide, high costs to farmers and/or traders especially when large quantities of maize are involved, reluctance of farmers or traders to comply with the law when there is no obvious LGB infestation, lack of manpower and facilities at checkpoints etc., have all contributed to this problem. The limitations have become more acute in the light of the large surplus amounts of maize produced in Tanzania in recent years.

Inadequate transport facilities coupled with the poor state of the roads has also resulted in large pile-ups of surplus maize under poor storage conditions, which may result in attack by LGB and other pests.

Although extensive training in LGB control measures and good storage management has been given to staff of the Plant Protection Division, to extension workers and to farmers, the training of staff of the Cooperative Societies has only just begun. Training for the latter group is considered essential as it is the Cooperatives who collect the bulk of surplus maize from farmers

REFERENCES

Gilman, G.A. and Nyakunga, Y.B. (1988). Control and containment of the Larger Grain Borer - The Tanzanian Experience. pp. 147- 160 in G.G.M. Schulten and A.J. Toet (Eds.). Proceedings of the Workshop on the Containment and Control of the Larger Grain Borer. Arusha, Tanzania, 16-21 May 1988. FAO, Rome, Italy. Report 2, 209 pp.

Golob, P., Chanjaroen P., Ahmed A., and Cox J. (1985). Susceptibility of Prostephanus truncatus (Horn) (Col.: Bostrichidae) to insecticides. J. Stored Prod. Res. 21, 141150.

Golob, P. and Hodges, R.J. (1982). A study of an outbreak of Prostephanus truncates (Horn) in Tanzania. Tropical Products Institute Report No. G164, vi + 23 pp.

Hodges, R.I., Dunstan, W.R., Magazini, I. and Golob, P. (1983). An outbreak of Prostephanus truncates (Horn) (Col.: Bostrichidae) in East Africa. Prot.Ecol., 5, 183-194.

Keil, H. (1988). Losses caused by the Larger Grain Borer in farm stored maize in the Arusha Region of Tanzania. pp. 28-52 in G.G.M. Schulten and A.J. Toet (Eds.). Proceedings of the Workshop on the Containment and Control of the Larger Grain Borer, Arusha, Tanzania, 16-21 May 1988. FAO, Rome, Italy. Report 2, 209pp.

Mushi, A.M. (1984). The Larger Grain Borer Prostephanus truncates (Horn) problem in Tanzania pp. 71-87 in Proceedings of the GASGA Workshop on the Larger Grain Borer, Prostephanus truncates. Slough, United Kingdom, February 24-25 1983. TPI, Slough. GTZ, Eschborn 139pp.

Map 1: Geographical distribution of LGB in Tanzania - April 1988

Table 1: Larger grain borer distribution in Tanzania 1981-1989

Zone / Region

Total number of villages

Cumulative number of infected villages

Percentage infested villages

'81 '82 '83 '84 '85 '86 '87 '88 '89 TOTAL
NORTHERN ZONE
Arusha 517 0 0 5 40 108 159 180 187 195 195 37.7
Kilimanjaro 423 0 26 115 177 214 289 293 295 295 295 69.7
Tanga 640 0 0 0 0 3 25 39 47 62 62 9.7
TOTAL 1580 0 26 120 217 325 473 512 529 552 552 34.9
LAKE ZONE
Mara 414 0 0 0 0 0 0 15 18 38 38 9.2
Mwanza 673 0 6 34 173 338 437 499 513 519 519 77.1
Kagera 528 0 2 6 29 56 64 72 82 83 83 15.7
TOTAL 1615 0 8 40 202 394 501 586 614 640 640 39.6
WESTERN ZONE
Kigoma 228 0 0 35 37 48 66 78 91 91 91 39.9
Tabora 419 62 92 186 273 400 408 410 413 413 413 98.6
Shinyanga 741 106 282 313 322 339 387 425 438 443 443 59.8
TOTAL 1388 168 374 534 632 787 860 912 935 940 940 67.7
CENTRAL ZONE
Singida 350 0 0 1 5 9 20 47 53 62 62 17.7
Dodoma 444 0 0 0 0 0 14 22 22 24 24 5.4
Morogoro 503 0 66 90 121 229 259 281 317 322 322 64.0
TOTAL 1297 0 66 91 126 238 293 350 392 408 408 31.5
SOUTHERN ZONE
Iringa 640 0 0 0 0 0 4 5 10 0 0 1.6
Mbeya 631 0 0 0 0 2 8 13 17 20 20 3.2
Rukwa 319 5 6 39 48 63 100 103 116 116 116 36.4
Ruvuma 324 0 0 0 0 8 10 17 20 40 40 12.3
TOTAL 1914 5 6 39 48 73 122 138 163 186 186 9.7
COASTAL ZONE
Pwani 399 0 0 0 0 0 0 0 0 0 0 0.0
Mtwara 483 0 0 0 0 0 0 0 0 0 0 0.0
Lindi 360 0 0 0 0 0 0 0 0 0 0 0.0
Dar es Salaam 24 0 0 0 0 0 0 0 0 0 0 0.0
TOTAL 1266 0 0 0 0 0 0 0 0 0 0 0.0
GRAND TOTAL 9060 173 480 824 1225 1817 2249 2498 2633 2726 2726 30.1

NOTE: Figures reflect the number of villages from which LGB out breaks have been reported at one time or another. However, in certain areas, especially the Southern Highlands, these outbreaks were brought under control through intensive campaigns and other control measures. Villages in those areas are presently not infested with LGB. Only rural and mixed type areas have been considered, urban type areas have been excluded.

 

Table 2: Intensive control campaigns in Tanzania February 1986 - February 1990

Date Region District Villages infested¹ Villages included Number of households

Actellic 50EC (ltr)

Actellic Super (kg)

Operational expenses*(TSh)

total household total household total household
Feb 1986 Iringa Iringa 4 8           300,000/=  
Jul-Oct 1988 Ruvuma Songea R. 9 8 2635            
Mar 1987 Ruvuma Songea R. 15 9 2665         300,000/= 67
June 1987 Mbeya Chunya 12 8           300,000/=  
Sep 1987 Dodoma Kondoa 7 14 7499 164 0.021     500,000/= 67
Oct 1987 Dodoma Mpwapwa 14 11 5729 132 0.022     200,000/= 35
Nov 1987 Morogoro Ulanga 18 48 14859 224 0.015     900,000/= 21
Dec 1987 Morogoro Kilombero 14 11 4580    
Jan-Mar 1988 Morogoro Kilosa 81 57 23512 753 0.032
Aug 1988 Tanga Pangani 7 3 835         200,000/= 63
Aug 1988 Tanga Handeni 11 6 1726
Aug 1988 Tanga Korogwe 14 5 600
 
Nov 1988 Rukwa Mpanda 100 65 23717 1800 0.076 2310 0.098 1,413,700/= 60
June-Aug 1989   S'wanga U. 3 4
June 1989 Dodoma Mpwapwa 21 14 6174 736 0.119 510 0.083 204,600/= 33
June 1989 Dodoma Kondoa
June 1989 Singida Iramba 23 29 11760 786 0.067 1410 0.120 467,585/= 40
June 1989 Mara Bunda 18 14 4227 365 0.074 400 0.081 300,000/= 61
June 1989 Mara Musoma 3 3 700
June 1989 Arusha Mbulu 30 9 4243 747 0.176 188 0.044 330,800/= 68
Aug 1989 Singida Manyoni 16 10 3689 155 0.042 2365 0.642 252,300/= 78
Oct 1989 Arusha Babati 34 8 4651 300 0.065 126 0.027 240,500/= 52
Oct 1989 Ruvuma Mbinga 13 16 5259 144 0.027 300 0.057 454,000/= 86
Oct 1989 Kagera Biharamulo                  
Jan 1990 Kilimanjaro Hai 35 3 3372 65 0.019 100 0.030 253,005/= 75
Feb 1990 Tanga Handeni 25 10 2543 126 0.050 105 0.041 500,000/= 197
Feb 1990 Tanga Korogwe
TOTAL 557 373 134,875 6737   7814   7,116,490/=  
TOTALS FROM NOVEMBER 1988 ONWARDS 321 185 70,235 5224   7814   4,416,490/=  
AVERAGES FROM NOVEMBER 1988 ONWARD         0,074   0.111   63

* Travel allowances on average approximately 75 % of total operational expenses; fuel, oil, repairs, etc. approximalely 25 %.
1 Total number of villages having been reported, at any time, to be infested with LGB prior to the start of the intensive control campaign.
2 Until November 1988 (Rukwa campaign) Actellic was used instead of Actellic Super, and often Cypermethrin in addition to Actellic 50EC.

Recent developments in Kenya on the ecology and control of Prostephanus truncatus

P.H. Giles and G.N. Kibata
NRI and KARI, Nairobi, Kenya

DISTRIBUTION

The Larger Grain Borer at present occurs mainly in the southern and south-eastern area of Kenya (see Figure 1 ) most of which is semiarid or arid where maize production is often difficult except in the mountainous «islands» and the northern slopes of Mount Kilimanjaro. Fortunately LGB has yet to be reported in the principal maize production areas in the highlands to the north and west. Obviously any control package developed must be appropriate for this area but at present, in the current absence of the pest, the R & D work has to be carried out in the south-east.

OBSERVATIONS ON ALTERNATE HOSTS

LGB has been recorded in pheromone traps far away from cultivated or stored maize or cassava. Adults of Prostephanus truncatus have been found in the partly dehisced pods of Cassia abbreviata Oliv. subsp. kassneri (Bak.f.) Brenan near Voi and dead cassava stems at Kiboko. Among other interesting records, the histerid beetle, Teretrius sp. has been found associated with the bostrichid Sinoxylon sp. and the lyctid Lyctus hipposideros Lesne in dead thorn tree wood near Taveta.

CONTROL STRATEGY

At present pest containment is partly achieved by restricting the movement of untreated maize and cassava from the infested zone and the insecticide treatment, by Government staff, of maize crossing the border from Tanzania as well as at markets and in farmer's granaries in Taita-Taveta District. With the planned registration of the dust mixture of 1.6% pirimiphos-methyl and 0.3% permethrin it is expected that farmers will be treating their own maize in the near future at a recommended rate of 50g per 90kg shelled grain.

PLANNED WORK PROGRAMME

If it is agreed that Teretriosoma nigrescens can be imported into Kenya, we plan to commence releasing it in two different agro-ecological areas (probably Kiboko at 1,000m altitude, 600mm annual rainfall and a mean temp. of 22.6°C; and Wundanyi at about 1,500m altitude, 1,400mm rainfall and a mean temp. of 16.4°C). intensive monitoring of infestation and grain damage will be undertaken in farmers' stores and in the field.

It is proposed to carry out socio-economic studies in the areas before release which will include the collaborating farmers in the monitoring programme, in order to study the post-harvest system and forecast constraints in the adoption of the LGB IPMI (Integrated Pest Management Initiative). Essential data on methods, grain quantities, consumption patterns and grain values will be collected with a view to assessing the cost-effectiveness of infestation control.

The predator release work is being carried out in cooperation with the IIBC which will be responsible for the quarantine, rearing, release and part of the study on the pest-predator ecology in the natural vegetation. The Teretriosoma release work is one component of the work programme of the NRI/KARI LGB Research Project in its wider objective of developing an integrated pest management initiative for the LGB.

Besides helping to establish a national LGB monitoring programme using pheromone-baited delta traps, studies will be carried out on the ecology of Prostephanus on the farm, particularly in the maize field in relation to the granary and surrounding vegetation, including dispersal and flight activity. Attention will be paid to the effect of variety, stage of maturity, husk cover and cob orientation. More information is required on the attractiveness of the pheromone traps and the factors affecting catch size.

Work is planned on the practical effect of climate on LGB rates of population increase with a view to forecasting loss levels if and when the pest becomes established in the Highlands. Chemical control work will be undertaken in relation to climate, grain form (husked v unhusked; cobs v shelled grain), insecticide type and dosage rate. The effect of application method and storage structure (including lofts above fires) will be evaluated at some sites.

Practical control recommendations arising from this R & D programme will be transferred to the extension Services through publications and training courses.

Figure 1: Distribution of Prostephanus truncatus in Kenya in 1990

 

Evaluation de la répartition du Prostephanus truncatus (Horn) (Col.: Bostrichidae) par utilisation de pièges à pheromone sur le territoire du Togo

J. Richter et A. Biliwa
GTZ et SPV, Lomé, Togo

ABSTRACT

A countrywide survey for the presence of Prostephanus truncatus (Horn) (Col.: Bostrichidae) in Togo using pheromone traps.

Between May and September 1989 a countrywide survey for the presence of Prostephanus truncatus was conducted by means of pheromone («Trunc-Call» I + II) baited traps. For this purpose the whole of Togo was divided into a grid of 175 squares, each measuring 20 x 20 kilometres. Up to 6 pheromone traps were distributed in each square and left untouched for two weeks. Traps were placed on and around buildings as well as in forests but never directly on storage structures. Of the 139 squares surveyed, 94% showed the presence of P. truncatus. The range of this storage pest is therefore now known to cover the production zones of the three most important subsistence crops in Togo; maize, manioc and sorghum. All three crops are subject to attack by P. truncatus.

——————————————————
The complete paper will be published in the Proceedings of the 5th International Working Conference on Stored Product Protection Bordeaux, France, 1990

 

Distribution, recherche et côntrole du grand capucin du maïs Prostephanus truncatus (Horn) au Benin

P. Fandoham*, B. Langer** et P. Mutlu**
* SPV et ** GTZ, Porto-Novo, Bénin

RESUME

Depuis la découverte du Grand Capucin du Maïs Prostephanus truncatus (Horn) au Bénin en janvier 1986, ce parasite est devenu un fléau dans la région du Sud-Ouest du pays (Département du Mono) ou il cause sur le maïs en spathes stocké en grenier traditionnel, des pertes en matière sèche atteignant en moyenne 20,5% après 6 mois de stockage. Le suivi de sa distribution par des prospections soit en observations visuelles ou à l'aide de pièges à phéromone révèle une évolution inquiétante de l'infestation vers l'intérieur du pays.

Divers tests d'insecticides et autres produits ont montré une protection acceptable du maïs en spathes avec les insecticides binaires composés de pirimiphos-méthyl + deltaméthrine. Ainsi, le Sofagrain (1,5% pirimiphos-méthyl + 0,05% deltaméthrine) est l'insecticide actuellement recommandé pour le traitement des greniers traditionnels à maïs à la dose de 50 g pour 100 kg de maïs en spathes.

La chaux éteinte se montre aussi efficace sur le complexe parasitaire du maïs. Après 5 mois de stockage, on a enregistré en 198910% de pertes en matière sèche comparé à 30% de pertes en matière sèche sur le témoin non traité avec la chaux éteinte.

INTRODUCTION

Le Grand Capucin du Maïs Prostephanus truncatus a été identifié pour la première fois. en janvier 1986, dans le Département du Mono, dans un village situé non loin de la frontière entre le Togo et le Bénin (Krall et Favi, 1986).

C'est un parasite qui est devenu un fléau dans le Sud Ouest du Bénin en ce qu'il cause de sérieux dégâts dans les stocks de mats en spathes en milieu paysan, et des études menées dans cette région en 1989 ont révélé des pertes importantes en matière sèche s'élevant en moyenne à 20,5% après 6 mois de stockage.

Depuis la découverte de ce parasite au Bénin, le Service National de la Protection des Végétaux a initié un programme de lutte à deux volets qui sont:

1) Le suivi de la distribution du parasite;
2) La recherche de moyens efficaces de lutte.

Figure 1: Lieu de provence mono dans la République Populaire du Benin et zones d'infestation de Prostephanus truncatus.

Figure 2: Carte d'infestation de Prostephanus truncatus dans la province de Mono - Benin

1. SUIVI DE LA DISTRIBUTION DE PROSTEPHANUS TRUNCATUS

Le programme de suivi de la distribution de P. truncatus est essentiellement conduit depuis 1985 dans le Département du Mono. Il est exécuté par des prospections régulières effectuées chaque année soit par des observations visuelles directes ou par des pièges à phéromone («Trunc-call» I et II). Jusqu'en 1990, les prospections ont été menées à deux niveaux qui sont:

- niveau greniers traditionnels à maïs et
- niveau champs de maïs,

l'objectif étant de surveiller de façon permanente la situation du parasite à ces deux niveaux.
Les Tableaux 1 et 2 font état des résultats obtenus de 1985 à 1990.

Ces prospections ont permis de constater une extension considérable de l'infestation de P. truncatus dans le Département du Mono avec une intensification beaucoup plus prononcée dans les zones limitrophes du Togo, maïs progressant de façon décroissante vers l'intérieur du Département (Fig.1 et 2).

Au niveau des champs de maïs, il a été enregistré un nombre impressionnant d'adultes de P. truncatus par piège à phéromone en 1989 (en moyenne 140 adultes) alors que les champs prospectés étaient à l'état jeune au stade de montaison. Cela pourrait être dû d'une part à une attraction des parasites par la phéromone des villages voisins vers les champs prospectés, maïs aussi à la présence du parasite sur d'autres substrats en dehors du maïs dans la brousse.

Hormis le Département du Mono, P. truncatus a été identifié en 1989 dans la région Nord-Ouest du Bénin précisément dans un village de L'Atacora puis en 1990 dans un village du centre du Bénin. C'est dire que le parasite tente de gagner tout le pays. A cet effet, une prospection générale a été prévue pour le mois de Décembre 1990.

2. RECHERCHE DE MOYENS EFFICACES DE LUTTE

La présence de Prostephanus truncatus au Bénin, surtout en régard à l'importance des pertes qu'il occasionne en milieu paysan, a obligé le Service National de Protection des Végétaux à revoir la stratégie de protection des stocks de produits agricoles. En effet, les recommandations de traitement chimique au pirimiphos-méthyl faites jusqu'alors aux paysans, étaient devenues caduques, ce produit s'étant montré inefficace contre P. truncatus. Nécessité était done de mettre en place des tests d'autres insecticides constitués pour la plupart d'un mélange d'organophosphoré et de pyréthrinoide (voir la liste des produits sur Tableau N° 3).

TABLEAU N° 1: Résultats des prospections faites au niveau des structures traditionnelles de stock age au mono sur Prostephanus truncatus Horn (Coleoptera, Bostrychidae) de 1985 à 1990

PERIODE METHODE UTILISEE Nbre
Sous-Préfet
visités
Nbre total
villages
prospectés
Nbre total
greniers
prospectés
Nbre
villages
infestés
OBSERVATIONS
1985 -1986 Pièges à phéromone (70) 4 12 70 0 Prospection fastidieuses
" Observations visuelles 2 48 446 13 "
1987 " 4 39 116 12 "
1988 " 8 48 124 5  
1989 Pièges à phéromone (792) 12 135 792 20  
1990 " (441) 9 107 441 37  

TABLEAU N°2: Prospections d'épis de maïs au champ dans zone infestée par Prostephanus truncatus

1. Observation externe d'épis preleves
ANNEE Nombre Champs
prospectés
Nombre Epis
observés
Nombre P. truncatus
retrouvés
Stade de Développement
du Champ lors prélèvement
1988 9 900 Néant Epiaison
1989 6 600 Néant Epiaison
2. Utilisation de pièges a phéromone
ANNEE Nombre Champs
prospectés
Nombre Pièges
observés
Nombre P. truncatus
retrouvés
Total Moy/Piège
Stade de Développement
du Champ lors prélèvement
1988 20 122 5707 46,8 Epiaison
1989 3 30 4185 139,5 Stade Montaison

N.B. Distance entre champs prospectés et villages avoisinants: 0,8 à 1,6 km.

Ces différents tests ont donné les résultats suivants:

- Sur maïs en épis déspathés ou en spathes les résultats étaient moins spectaculaires que sur maïs grains. Cependent, la meilleure protection du maïs stocké dans ces conditions est assurée par les binaires composés de pirimiphos-méthyl + deltaméthrine (Sofagrain), le binaire pirimiphos-méthyl + perméthrine (Actellic-Super) ayant été peu efficace (Fig. 3 et 4).

Le traitement du maïs en spathes avec la chaux éteinte (Ca (OH)2) avait aussi donné des résultats intéressants sur le complexe parasitaire, les pertes en matière sèche ayant été maintenues à moins de 10% jusqu'à 5 mois de stockage. Ceci justifie l'attention particulière dont bénéficie cet hydroxyde de calcium au niveau du Service National de la Protection des Végétaux (Fig. 5).

- Sur maïs grains, les binaires composés de pirimiphos-méthyl + deltaméthrine se sont aussi avérés les plus efficaces, les dégâts ayant été généralement maintenus à moins de 10% jusqu'à 6 mois de stockage (Fig. 6).

Enfin, pour mieux se préparer à la lutte biologique contre P. truncatus, le Service National de Protection des Végétaux a engagé depuis 1989, une étude d'évaluation des dégâts et pertes causés par le parasite dans les greniers traditionnels de maïs. Cette évaluation a permis de constater en 1989 que les pertes occasionnées par les parasites des stocks sont importantes dans les stocks infestés par P. truncatus (20,5% après 6 mois de stockage) (Fig. 7 et 8).

Les études se poursuivront après lâchers d'ennemis naturels en vue d'une correcte évaluation de la lutte biologique.

3. MESURES DE LUTTE CONTRE PROSTEPHANUS TRUNCATUS

La nécessité de lutter efficacement contre le Grand Capucin du Maïs a entraîné les zones infestées par ce parasite au Bénin, la révision pure et simple du programme de protection des stocks. Les mesures de lutte préconisées tiennent compte des résultats obtenus à l'issue des différents tests d'insecticides effectués.

TABLEAU N° 3 PRODUITS TESTES SUR MAÏS AU MONO
(Lutte contre P. truncatus) 1987 à 1990

——————————————————————————————
- Actellic - Super PP: (1,6 % Pirimiphos-méthyl + 0,3 % Perméthrine)
doses testées: 50 g / 100 kg et 100 g / 100 kg maïs despathés et grains

- Actellic PP: (2 % Pirimiphos-méthyl) + K-othrine (0,2 % Deltaméthrine) un mélange réalisé par l'expérimentateur
doses testées: 50 g / 100 kg maïs despathés et grains

- Sofagrain PP: (1,5 % Pirimiphos-méthyl + 0,05 % Deltaméthrine)
doses testées: 50 g / 100 kg et 100 g / 100 kg maïs despathés et grains

- Poudre de Neem: Fabriquée juste avant la mise en place d'essai
doses testées: 200 g /100 kg et 500 g /100 kg maïs despathés et grains

- Chaux: doses testées: 300 g /100 kg et 500 g /100 kg maïs en épis en spathes et grains
——————————————————————————————

Ainsi dans ces zones:

- L'utilisation de pirimiphos-méthyl (Actellic PP) simple a été interdite,

- Le Service y recommande l'utilisation de l'insecticide binaire Sofagrain ( 1,5% pirimiphos-méthyl + 0,05% deltaméthrine) à la dose de 50 g pour 100 kg de maïs (7,5 + 0,25 ppm) sur maïs en spathes ou grains. Maïs compte-tenu du fait que les paysans acceptent mal le stockage en grains à cause des difficultés de déspathage et d'égrenage, il a été recommandé le traitement du maïs en spathes. A ce titre, un programme de prévulgarisation a été mis en oeuvre depuis août 1990 dans le Département du Mono, sur le traitement du maïs en spathes avec Sofagrain. Ainsi dix (10) greniers traditionnels à maïs ont été traités avec ce produit en guise de test en milieu paysan.

REFERENCES

Krall S. and Favi F. (1986) Further distribution of the Larger Grain Borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) in West Africa. FAO Plant Prot. Bull. 34, 213-214

Figure N° 3 Maïs despathé: Evolution du pourcentage de pertes de poids en MS (MPE)

Figure N° 4 Maïs despathé: Evolution du pourcentage de pertes de poids en MS (MCP)

Figure N° 5 Maïs en spathes: Evolution du pourcentage de pertes de poids en MS (MCP)

Figure N° 6 Maïs en grains: Evolution des dégâts

Figure N° 7 Pertes causées pendant grande période Campagne agricole 1989 - 1990

Figure N° 8 Pertes causées pendant petite période Campagne agricole 1989-1990

 

Situation report on the Larger Grain Borer in Ghana

G.A. Dixon
Plant Protection Service, Accra, Ghana

The LGB is still a major pest in Ghana. Surveys conducted with pheromone traps confirmed the presence of LGB in the Volta Region of Ghana. Monitoring exercises conducted by the Post Harvest Development Unit of the Ministry of Agriculture confirmed that apart from Volta Region, which shares a common border with Togo the remaining regions of Ghana are tree from LGB attack. Though species of storage grain pests were trapped in the Eastern Region of Ghana they were not identified as the noxious LGB.

Since the survey and the visit of the FAO consultant, who recommended short and long term control programmes, the Ministry of Agriculture has introduced a Containment Programme. Under this programme, the Plant Protection Service of Ghana was charged to set up road check points as an internal quarantine measure to check and treat all maize, dried cassava chips and empty jute and polythene bags coming from the Volta Region to other parts of Ghana. Furthermore at all our international border posts with Togo, the personnel of the Plant Protection Service have intensified phytosanitary activities to check and also treat all in-coming maize, dried cassava chips and all empty bags.

FARMERS EDUCATIONAL MEETINGS.

Farmers fora have been organized in the infested areas to create awareness of dangers of the LGB to Ghana's maize industry and also to educate the farmers on how to control the LGB.

TRAINING.

There have been in-country training courses for technical staff of the Extension Services, Plant Protection Service and the Post Harvest Development Unit.

Not all the recommendations in the FAO consultant's report have been implemented; nevertheless the Ministry of Agriculture is doing all it can to initiate the chemical control of the LGB. Actellic Super is already available in the country for the chemical control programme. With the success of the biological control of the cassava and mango mealy bugs in Ghana the Ministry of Agriculture of Ghana is of the opinion that the LGB can also be controlled effectively by biological means.

We in Ghana therefore, look forward to any international institution, which will collaborate with the Government of Ghana for the control of this noxious pest.


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