Farmers zero-in on insect pests

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Larger grain borer (Prostephanus truncatus): Risk assessment and control in farm maize stores
Validated RNRRS Output. Home List by Audience List by Topic

Armed with new knowledge, farmers are taking action to reduce damage to crops in storage. A risk warning system, based on a model of insect flight activity and climate data, enables extension services to warn them of anticipated increases in the threat from a pest known as the larger grain borer (LGB). In addition, using targeted insecticide applications, farmers can reduce by at least 70% the amount of pesticide applied to their crops, zeroing-in on the portion they will be consuming during the storage season. LGB can be devastating to maize and dried cassava. Without a warning system, the sporadic nature of LGB outbreaks can take farmers by surprise. The new techniques, developed and validated in Ghana and Tanzania, cut losses – and costs – considerably.

Project Ref: CPH42:
Topic: 5. Rural Development Boosters: Improved Marketing, Processing & Storage
Lead Organisation: Natural Resources Institute (NRI), UK 
Source: Crop Post Harvest Programme


Current Situation
Environmental Impact


Research Programmes:

Crop Post-harvest Programme

Relevant Research Projects:

  • R6684 (1996 – 1999) Risk Warning to Farmers of Larger Grain Borer Infestation and Reduced Pesticide Treatment in Farm Maize Stores (Ghana)
  • R7486 (1999 – 2002) Development of IPM techniques for the control of Larger Grain Borer and effective management of household food grain stocks in sub-Saharan Africa (Ghana)
  • R8265 (2002 – 2005) Improving household food security by widening the access of small-holder farmers to appropriate grain store pest management (Ghana)

Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK. Contact Person:  Dr Rick Hodges, Email:  Tel: +44 (0) 1634 883813

Lead institute (R8265): Ministry of Food and Agriculture, Tamale, Ghana. Contact Person: Mr Fusieni Andan, Email:; Tel: +233 208164891. Dr Samuel Addo, Email:

Research Outputs, Problems and Solutions:

To African small-holders, food and financial security are often represented by stored grain and other commodities.  These are subject to attack by a complex of insect pests including the larger grain borer (LGB); an especially damaging species from Central America now endemic in many parts of sub-saharan Africa.  LGB can be utterly devastating to maize and dried cassava, with infestation often reducing sound stock to dust in a relatively short time.  Moreover because of its recent introduction to Africa and the sporadic nature of its outbreaks – over time and space – farmers (and extension staff) are frequently been taken by surprise.  To tackle this problem an LGB risk warning system, based around a model of LGB flight activity driven by climate data, was completed in 2002 that enables well equipped extension services to warn farmers of coming bad years and so take action to reduce the severe damage expected.  Typical action by farmers is to apply insecticide to their stored crop but this is expensive.  To reduce the costs of treating the portion of the crop that farmers will be consuming during the storage season, a method of targeted insecticide application was developed.  This reduces by at least 70% the amount of pesticide applied to stores but still provides good protection.  This is achieved by treating only the bottom 30% of traditional maize cob granaries or small bulks of maize grain.  However, maize for longer-term storage may require the usual full treatment.

Types of Research Output:

Product Technology Service Process or Methodology Policy Other

Major Commodities Involved:

The commodities for the LGB risk warning are maize and dried cassava.  For targeted insecticide treatment maize is currently the only commodity included, other commodities cannot be included without further research.

Production Systems:

Semi-Arid High potential Hillsides Forest-Agriculture Peri-urban Land water Tropical moist forest Cross-cutting

Farming Systems: 

Smallholder rainfed humid Irrigated Wetland rice based Smallholder rainfed highland Smallholder rainfed dry/cold Dualistic Coastal artisanal fishing

Potential for Added Value:  

Other relevant outputs would relate to improved methods of maize/cassava storage.  Good examples would be the substitution of synthetic pesticides by diatomaceous earths on maize and sorghum (R8179) and the output cluster ‘Better grain stores for farmers and traders’ (R6311, R6658, R6502, R8265).


How the outputs were validated:

Please provide brief description of method(s) used and consider application, replication, adaptation and/or adoption in the context of any partner organisation and user groups involved.  In addressing the “who” component detail which

group(s) did the validation e.g. end users, intermediary organisation, government department, aid organisation, private company etc…  This section should also be used to detail, if applicable, to which social group, gender, income category the validation was applied and any increases in productivity observed during validation . 

Risk warning system – this is based on a flight activity model that was developed in Ghana in a woodland savannah zone and validated in Tanzania in a semi-arid short grass steppe zone.  Project staff entered historical Tanzanian climate data into the model and predicting LGB flight activity to compare with the observed LGB flight activity record for that time. The model worked extremely well, so demonstrating that it could be applied outside Ghana and in other habitats.  However, this was only a validation of the model and to date the risk warning system, which includes taking a warning of a coming bad year to a farming community, has not been fully implemented to test whether farmers can actual benefit from it.

Targeted insecticide treatment – in Ghana, following on station trials, targeted treatment was validated by 25 subsistence farmers in their own granaries using partial treatment of the bottom 30% of maize cobs using Actellic Super emulsion.  In subsequent farmer assessment meetings, with a total of 66 farmers, the method was considered to have offered effective protection of stored maize cobs against LGB and other pests. In Zimbabwe, the method was validated in on-station trials in brick-built farm stores with compartments holding maize grain in bulk. The bottom 20% or top 10% and bottom 20% of maize grain was treated with Actellic super or a diatomaceous earth formulation.  All treatments provided good control of insect pests.

Where the Outputs were Validated:

Risk warning model – was first validated in Tanzania, in 2000, in a semi-arid area where the farming system was smallholder rain-fed and dry compared with smallholder rain-fed and humid in which it was developed.  The social group involved is not directly relevant at this level since the predictions of the model were not actually used to advise farmers on the need for pest management against LGB; however this is a further important step that has still to be investigated.  In a second technical validation, the model was tested in a hotter dryer semi-arid area in Northern Ghana again the model worked well but did require some adjustments to ensure that its predictions were accurate.

Targeted insecticide treatment – was validated in five villages in the Volta Region of Ghana with small-holder maize farmers in 2002, in a rain-fed, humid farming system.  In Zimbabwe, validation was done in on-station trials close to Harare in 2000.

Current Situation

Who are the Users?

Risk warning model – is not currently being used.

Targeted insecticide treatment – was introduced to farmers in five villages in Ghana in 2002.  During an assessment in October 2006, in the same villages, few insect infestation problems were reported, most farmers were not now storing maize cobs but shelling their grain and then applying pesticides before storage in bags, one possible recommendation for reducing LGB damage that has been extended since the mid-1990s.  Relatively few were farmers using targeted treatment of cobs except in two villages where not more than about 15 farmers were using it.

Where the outputs have been used:

Risk warning model – not currently being used.

Targeted insecticide treatment – in two out of the five villages used in validation studies in the Volta region of Ghana

Scale of Current Use:

Risk warning model – not currently being used. 

Targeted insecticide treatment – limited to not more than 15 farmers in two villages.  It seems doubtful that use is spreading due to the predominance of earlier extension messages to shell maize cobs, treat all the shelled grain with insecticide and store it in bags.

Policy and Institutional Structures, and Key Components for Success:

Risk warning system – to date a suitable institutional structure to support the full implementation of this system has not been found. 

Targeted insecticide treatment – the technique is simple in principle and easy to apply so that very little training and support is required to enable the method to be extended by competent agriculturalists.  The method can therefore be easily promoted by any organisation offering services to farmers (agricultural extension service or NGOs) in Tanzania, Uganda, Zambia, Malawi, Zimbabwe, Mozambique, Ghana, Nigeria or Sierre Leone.

Environmental Impact

Direct and Indirect Environmental Benefits:

There is a positive environmental impact of targeted pesticide use in that less pesticide will be used in the protection of individual grain store.  This may however, be offset in that the use of pesticide treatment will become more affordable, hence for some poorer households more likely to be used.  Overall it is therefore likely that the effect will be neutral.

Adverse Environmental Impacts:

No environmental impacts expected.

Coping with the Effects of Climate Change, or Risk from Natural Disasters:

Both risk warning and targeted pesticide use increase the amount of food available for consumption and sale.  For individual families this could be 5% to 10%.  This can be an important bridge between harvests and can be an important contribution to reducing hunger.

Relevant Research Projects, with links to the
Research for Development (R4D) web site
and Technical Reports:

R4D Project Title Technical Report
R6311 Improving the use of phosphine for small-scale fumigation of grain on farms
R6502 Mud based silos: farm stores for cereals
R6658 Epidemiology and crop loss assessment of rice nematodes in West Africa.
R6684 Risk warning to farmers of Larger Grain Borer infestation and reduced pesticide treatment in maize stores  51 MB
R7486 Development of IPM techniques for the control of Larger Grain Borer, and effective management of household food grain stocks in sub-Saharan Africa (2nd phase)
R8179 Small-scale farmer utilisation of diatomaceous earths during storage
R8265 Improving household food security by widening the access of smallholder farmers to appropriate grain store pest management
  • Establishing the future otential for the use of mud silos by the smallholder farmers: an assessment of mud silos promotion in the Northern Regio of Ghana