Pearl millet, Pennisetum americanum L. occupies a large proportion of the area growing millets in Africa. Consequently the insect pests that attack this species have received attention over other millets. A list of the major species is presented. Actual data on losses due to insect pests on pearl millet are not readily available. Crop loss assessment methods using incidence and damage ratios are discussed. Quantitative losses determined from insecticide trials at research station are also presented.

In many parts of Africa, field sorghum is attacked by a number of insect pests, notable among them being the sorghum shootfly, a range of lepidopterous stem borers, midge and a complex of head bugs. Studies on yield losses caused by these insects are scanty, yet such information is essential in formulating an IPM strategy for the crop. This study, therefore, describes the various methods of assessing and quantifying the on-farm (pre-harvest) yield losses caused by the above insect pests.

Maize is the single most important food cereal in eastern and southern Africa. Yield levels, however, are among the lowest in the world. Among the major constraints limiting production are the insect pests. Objective assessment of damage and losses caused by these pests are lacking in several countries within the region. This paper discusses some of the methodologies available, and how they can be used to estimate the losses caused by insect pests under different situations. It emphasizes the need for standardization of the methodologies, so that information generated from different countries can be compared. This will promote collective action to combat the pest menace and increase food security.

The rice plant is an extremely versatile crop that is grown under both tropical and sub-tropical conditions in various ecological conditions. Several insect pest species attack the rice crop at all growth stages while in the field. The nature and magnitude of crop loss due to insect pest attack in tropical and sub-tropical Africa are highlighted. Reliable evaluation techniques for establishing relation between insect pest intensity/damage and crop loss are outlined. Natural insect pest infestation in the field, manipulation of pest infestation with chemicals, caging to confine or keep out insect pests and the use of resistant varieties as methods of estimating on-farm losses due to insects are discussed. In tropical Africa, the major constraint to the determination of crop loss due to insect pests of rice is research-related.

Armyworm, Spodoptera exempta (Wlk.) feed on cereals and grassland in eastern and southern Africa. Data on the yield losses and economic effects of an attack on cereals is sparse. They can be an indirect cause of cattle deaths. The need to examine the situation at the farm level has been recognized. A national survey was conducted in 1987, and is currently being analysed. The work entails identifying representative areas and farmers, completing a questionnaire with each farmer, noting the frequency of outbreaks experienced, the farmers' response, the level of government support, the effectiveness of control measures and the costs incurred. Proposals are outlined for future work within the region to determine the reduction in cereal yields due to this insect and to set up action thresholds for control activities. A major difficulty with the survey approach is the disaggregation of various loss-causing factors. At a sub-sample of survey sites, where outbreaks are present, the damage to the crop and the subsequent yield of the damaged crop or the planting of a replacement crop would be recorded to build up data from which action thresholds might be determined.

This paper describes briefly four different locust species that constitute potential widespread danger to agriculture and pasture in the eastern, central and southern Africa region. Particular reference is made to the red locust, Nomadacris septemfasciata Serville which mostly feeds on monocotyledonous plants. Reference is also made to the African migratory locust, Locusta migratoria migratorioides R&F; the brown locust, Locustana pardalina Walker; and the desert locust, Schistocerca gregaria Forskal. There were frequent reports of damage to cereal crops by the red locust during the most recent plague of the 1930's. However, since that time only a few yield loss data are available owing, primarily, to the fact that locust infestations have mostly been irregular and confined within their natural breeding areas, away from crop land. The paper provides general background information that should enable evaluation of locust incidence in the region and assessment of consequent cereal crop production losses.

Soil pests are defined as those in which the damaging stage of the life cycle lives in the soil. In Africa the most important soil insect pests are termites, followed by the larvae of various beetles (particularly scarabs), and by millipedes which are included here as they damage plants in a similar way to some insects.

The most important cereals in Africa are maize, sorghum and millet, with wheat and rice increasing in importance. Attack by soil pests usually begins on the root system and yield losses result from plant mortality, lowered translocation of water and nutrients, increased susceptibility to pathogens, or lodging with subsequent damage to grain on the ground from various vertebrates, invertebrates and saprophytes.

Data have often been presented as ‘percentage of plants damaged’ or ‘infested’ and bear little relationship to yield loss, as this depends on the severity and timing of attack. A succession of soil pests can attack the plants from seedling to maturity. Early season attacks can result in compensatory growth by remaining plants leading to overestimation of yield loss by simple estimates of plants damaged. Direct estimation of yield loss is time-consuming and few such studies have been made. However, methods are presented here for termites and maize which could be adapted for other pests and crops. Indirect estimates using pesticides are more common and, in general, indicate that an integrated pest management approach to soil pests is required.

The methods for and the problems of recognizing bird and rodent damage are described. For birds the methodology for assessing the damage, and the necessary statistics for determining sample design and sample size exist. Damage is measured either by visual estimation of the percentage loss (sorghum, maize, millet) or by weighing/comparing of damaged/undamaged spikes/panicles (wheat/rice). Sampling usually involves randomly selected transects. A system is also available for assessing bird damage over large areas of District, Regional or even countrywide levels involving aerial surveys of crop hectarage and ground teams sampling damage levels at randomly selected points.

For rodents, the methodology is less well established but damage in the field is usually quantified in terms of the percentage of rows of cereals destroyed at germination (maize) or by the number of cut stems compared to uncut stems in sample quadrats (wheat, barley).

Manpower and resources for bird control do not often extend beyond control operation to damage assessments. As a result the necessity for and success of bird control has to be evaluated in terms of diminishing farmer complaints or expressions of farmer gratitude rather than objectively in terms of crop saved or cost-effectiveness. It is suggested that in the long run, emphasis must inevitably switch to damage assessments as the economic pressures on Africa continue to increase.

Loss estimates are needed to develop rational economical control measures and to impress upon administrators and donors for efficient disease management. Losses can be actual and potential, incidental and regular, transitional and structural, primary and secondary. Various measuring principles and development of methods to estimate losses are discussed.

During the two years research 1983–1985 on traditional maize granaries in Togo, we studied three methods for loss assessment which are discussed by the FAO: the count and weigh method, the standard volume/weight method and the thousand-grain mass method.

In general, between 80 and 90% of the overall losses were caused by insect feedings. Besides Prostephanus truncatus (Horn), the most important storage pests were Sitophilus zeamais (Motsch.), Tribolium spp. and Cathartus quadricollis (Guèr.). Best results were given by the count and weigh method. The significantly highest losses of dry weight (12–13%) were found after 6 months in stored hybrids. At the same time, local varieties appeared much more adapted to traditional storage methods, exhibiting losses of only 3% under the same conditions. Lowest level of losses (<1%) were observed in regularly smoked granaries in the mountain regions. The mean losses of dry weight during primary season were found to be 6.4% after 6 months, while after a storage period of 4 months during the secondary season, losses were as high as 8%. In Togo, P. truncatus was observed for the first time in spring 1984. Because of the different damage P. truncatus causes on corn, a newly developed sample weight method was examined in an additional test. After 6 months of observation, this dangerous pest caused serious losses up to 30.2%.

Since it was first reported in Tanzania in 1981 the Larger Grain Borer (LGB) has spread from a small area in the northwest of the country to 17 of the 20 regions. Only in the extreme south, along the Mozambique border, has the pest not been found. It has also become established in Kenya, Burundi, Togo and Benin.

LGB can cause very high weight loss in farm stored maize and dried cassava, commodities on which it is able to breed. After 5 months storage during the dry season in western Tanzania, mean losses of 9% were found, a much higher level than losses of less than 1% which would be expected in LGB-free areas in East/Central Africa.

Application of 0.5% permethrin dust at 2.8 ppm provides excellent protection against LGB when applied to loose maize grain for 1 year. However, the storage of shelled maize predisposes towards the development of Sitophilus species which can result in high losses being sustained. A “cocktail” of permethrin and pirimiphos-methyl, applied at 3.3 and 17.7 ppm respectively, successfully controls all storage pests and is currently being used in an extensive control campaign in Tanzania.

A multi-donor funded control and containment campaign, co-ordinated by FAO, has been in operation in Tanzania since 1984. The programme is comprised of a training element for agricultural staff and several field extension campaigns which assist with insecticide distribution and with dissemination of information to farmers. The primary objectives of the programme are to reduce farm storage losses and to contain LGB within the areas it is now found. In some regions, where LGB is relatively isolated, attempts are being made to eradicate it.

Storage method encompasses the patterns and periods of storage as well as particular storage techniques. Storage management is therefore a major determinant of post-harvest losses in stored cereals: affecting the magnitude of losses and their susceptibility to reduction. Key issues are the location and scale of grain storage which, in most developing countries, involves both rural domestic storage and larger seal “buffer” storage at district centres, commonly near towns.

Various storage techniques are described and discussed against the background of available informatio on storage losses and with regard to the common patterns and periods of storage in Africa at the farr level and in “centralized” storage. The importance of long-term development planning for cereal crop production and utilization is stressed as a major factor in storage pest management and the reduction of storage losses.

The handling of imported food grains is discussed with regard to storage management problems arising from moisture content/relative humidity equilibria as affected by grain temperature.

I would like to extend my expose to cover also dry pulses and groundnuts which make up, together with cereals, the greater part of grains stored at farm and village level.

To begin with, we should make a distinction between, on the one hand, countries with a rather good road network and more or less workable grain marketing institutions, where farm storage has much decreased and in some cases nearly vanished, and on the other hand, countries where the isolation of producers and absence of good marketing institutions have helped to conserve the traditional storage methods on the farm, and occasionally, in the villages. As examples of the first type of countries, I would indicate Kenya and Zambia and of the second type, Chad and a large part of the Sudan.

FAO has in the past given much attention to the development, dissemination and use of methods to assess pre- and postharvest crop losses. The experience gained shows that losses vary with location, crop, pest and differ from year to year. The collection of data on a national or regional basis is expensive, since data have to be collected over a number of years. Therefore, loss assessment is now mainly used as a tool to develop loss reduction strategies and to assesss the cost-effectiveness of introduced methods.

A reservation is made with respect to the quoting of data on losses, without giving information on how these data were collected and interpreted, because data presented in that way can easily be misinterpreted.

Many useful crop preharvest loss assessment methods are presently available for the researcher, but there is, however, an urgent need for simple methods for use by extensionists and farmers in other situations. The developed methods to assess postharvest losses in grains are adequate.