Lepidopteran stemborers (Chilo zacconius Bleszynski, Chilo diffusilineus de Joannis and Maliarpha separatella Ragonot) and diopsid flies (Diopsis spp.) are economically significant insect pests of rice in Burkina Faso. The objective of this study was to monitor damage trends and the pre-imaginal populations of these insects on two host plants, cultivated (Oryza sativa L.) and wild rice (Oryza longistaminata Chev and Roehr). The study was conducted over four consecutive rice crop seasons from 1999 to 2001 in three irrigated rice-growing locations in western Burkina Faso. Sampling of cultivated rice was conducted monthly in 1 m2 quadrates in 100 randomly selected farmers' fields. Data on wild rice were collected monthly from each of the three locations using 500 tillers that were plucked at random and dissected. Results showed that in the absence of a rice crop lepidopteran stemborers and diopsid flies are able to survive on O. longistaminata, which can host the pre-imaginal populations of these insects throughout the year. Damage caused on cultivated rice varied across farmers' fields, seasons and phenological stages of the plants. With 8% the highest average extent of ‘whiteheads’ was recorded during the dry season. These results are important elements in the design of a sustainable management strategy for these insect pests.

The distribution and existing control measures for three important Chilo spp. (C. partellus, C. orichalcocilliellus and C. sacchariphagus) to cereal crop production in 10 east African countries and their neighbouring Indian Ocean Islands are reviewed. Various cultural, biological, host-plant resistance/tolerance and chemical control methods developed in the past 30 years of cereal research programmes are discussed. Cultural methods are very effective on Chilo spp. control, but are not widely practised. Although several effective natural enemies have been identified for Chilo spp., very few systematic programmes of their utilization have been effected. Several resistant/tolerant maize and sorghum lines have been reported, but they are not yet fully used. Chemical control though effective, has proved rather unsuccessful in traditional agriculture. Suggestions to incorporate these control methods in Integrated Pest Management (IPM) programmes for Chilo spp. in different places in the region are given.

Female sex pheromone components have been identified for seven species of Chilo, pests of cereals and sugar-cane. Synthetic pheromone blends for C. suppressalis, C. sacchariphagus, C. sacchariphagus indicus, C. auricilius and C. zacconius have shown satisfactory attractiveness to male moths in the field. Blends for C. partellus and C. infuscatellus seem to be incomplete. Pheromones and related compounds have been investigated for control of C. suppressalis by mating disruption in the Philippines, Japan, Spain and Korea. These studies have shown not only trap catch reduction, but also reduced viable egg production in field cages and effective control of damage by this pest on areas up to 60 ha. Initial studies have been carried out on control of C. sacchariphagus by mating disruption in Mauritius, and both the pheromone and an inhibitor have been shown to cause trap catch reduction of C. auricilius in India. Attempts have been made to control C. sacchariphagus indicus by mass trapping in India.

The paper reviews the work done on the population patterns of Chilo spp. in relation to the phenological stages of sorghum, maize and millets. The stem borer Chilo partellus entered sorghum and maize crops at 2–3 weeks after emergence and continued till harvest. There were 3–4 peaks of larval population during a cropping season. Such studies not only reveal the relationship between the larval population density and the phenological stage of the plants at infestation time, but are also helpful in scheduling and timing pest management strategies.

Most field experiments in the microbial control of Chilo spp. have been performed using strains of Bacillus thuringiensis (B. t.). Generally, low levels of control were obtained, which is probably due to the relatively narrow host range of the B. t. strains used. B. t. formulations and different B. t. strains obtained from overseas culture collections or isolated from material collected in Kenya were screened for activity against C. partellus.

C. partellus was found to be susceptible to commercial preparations based on B. t. kurstaki only. The screening and bioassay work on identified B. t. strains showed differences in the toxicities of the various subspecies groups for C. partellus. There were also differences in the toxicity of isolates within the same subspecies. The most toxic exotic strain obtained was B. t. entomocidus. Excellent control of C. partellus larvae, on artificially infested plants, was obtained. Plant damage was significantly reduced and yield levels increased by 5 to 7 times over the untreated controls. Three strains, M-44–2, A-3, and A-C-2, gave the best levels of plant protection.

Different methods of applying the pathogen to the crop have also been investigated. Aqueous suspensions and a granule/powder formulation have given very good levels of borer control in screenhouse experiments.

A review of the losses caused by various species of Chilo, methodologies adopted for the assessment of losses and information generated on the models for the effect of Chilo species on the yield of graminaceous crops is given.

Several species of Chilo occur on sugar-cane, out of which five have major pest status. Infestation by these pests causes losses in cane yield and sugar recovery. There are constraints involved in the use of cultural, mechanical and chemical control measures on a large scale, but the nature of the crop facilitates adoption of biological control. Many species of natural enemies occur in the sugar-cane agro-ecosystem, which is relatively less disturbed. They play a significant role in maintaining the pest populations at reasonably low level.

In biological control, the egg parasite, Trichogramma spp., has been widely used with varying results. Among the larval parasites, Apanteles flavipes (Cameron) and Sturmiopsis inferens Townsend have been used on a limited scale and need further testing in other countries. The exotic tachinids introduced, failed to establish against Chilo spp. Not much work has been done on the predators, though the native predators play a significant role in reducing the pest densities. Among the entomopathogens, granulosis virus infecting Chilo infuscatellus Snellen has shown promise in the control of this pest and needs further evaluation in other agro-climatic regions. Future thrust for biological control of Chilo spp., in sugar-cane has also been indicated.

Knowledge on the natural enemies of graminaceous stem borers is outlined, with special reference to mortality of Chilo spp. as crop pests in Africa. The quantitative scanty information available suggests that over 90% mortality of eggs and larvae takes place before the larvae become established as borers in the crop and that mortality of the older larvae and pupae is much lower. Possible manipulations of natural enemies to increase mortality further are reviewed. In view of the largely negative results of past classical biological control introductions the prospects do not appear very promising. However, the results do indicate some possibilities which should be investigated, notably trials with Apanteles spp. (Braconidae) and intra-continental redistribution of important species with restricted distributions. For short-term biological control, development of microbial biopesticides seems a more promising strategy than augmentation of insect parasitoids by breeding and release, particularly on small farms. A third possibility, enhancement of the action of native natural enemies by environmental manipulation, merits more attention as part of an integrated crop production approach to the improvement of the quantity and reliability of yields for the small farmer.

Chilo species constitute one of the three major lepidopterous rice stem borers in Africa and their occurrence stretches across the different rice ecosystems; two major species, C. zacconius Bles. and C. diffusilineus (J. de Joannis) are found in West Africa, while C. partellus (Swinh.) and C. agamemnon Bles. appear to be the predominant species on rice in East and North Africa, respectively. A brief note is given on some aspects of the biology, especially the life history and behaviour of C. zacconius. Control measures are discussed as well as an integrated approach towards management based essentially on growing resistant varieties, conservation of natural enemies and adjusting planting dates.

Chilo spp. are among the most important stem borers of sugar-cane in the Old World. Chemical control is not very effective mainly because of the concealed habit of the borer larvae. Efforts have therefore mostly been directed to alternative methods of control such as cultural practices, varietal resistance, biological control and the use of sex pheromones. Varieties are not normally bred for borer resistance but very susceptible ones tend to eliminate themselves at the early stages of selection. Susceptibility is normally assessed on promising and released varieties. Classical introduction of exotic parasites has more or less reached a saturation point and biological control tends to be oriented towards the possible use of new or cross-bred strains. The importance of entomopathogens as a control component against Chilo spp. needs further studies. A great potential exists in the use of sex pheromones mainly as a means to disrupt mating, as shown by the promising results obtained through trials carried out in various countries. It is very important that the various methods of pest control available be used in combination with one another, taking into account the natural limiting factors of the environment. This would be an important contributing factor towards an objective of optimum yield at minimum cost in the management of Chilo spp. on sugarcane.

Eight species of the genus Chilo Zincken have been reported from maize, sorghum and millet. Out of these, four species C. agamemnon Bleszynksi, C. diffusilineus de Joannis, C. orichalcociliellus (Strand) and C. partellus (Swinhoe) are known pests of these crops. Others, C. sacchariphagus (Bojer) and C. suppressalis (Walker), are serious pests of sugar-cane and rice and have been occasionally recorded attacking maize, sorghum and millet. Their distribution is discussed. About 50 species of parasitoids and predators reported from various Chilo spp. are listed. Possibilities of biological control are discussed.

Twenty-seven species of Chilo which infest graminaceous crops are listed. The effects of various cultural practices such as time of planting, plant density, field sanitation, tillage, mulching, intercropping, proper fertilizer and water management on field populations of Chilo spp. are discussed. These practices have great potential as components of IPM for resource-limited farmers in the tropics.

Several species of Chilo are serious pests (stem borers) of sorghum, maize, rice and sugar-cane. Studies on genetics of resistance to Chilo species have been carried out only In a few cases. In maize and sorghum resistance to C. partellus, measured in terms of leaf-feeding, dead hearts and stem-tunnelling is polygenic. Both additive and non-additive gene effects are important in the inheritance of resistance to C. partellus. However, the importance of additive and non-additive gene effects in determining resistance, varies with the resistance parameter in two crops. Resistance to leaf-feeding and stem-tunnelling is governed predominantly by additive genes, while both additive and non-additive genes are important in the inheritance of dead hearts. The non-additive gene action, however, is of higher magnitude and more important in the inheritance of resistance to dead hearts in maize than that in sorghum. Recurrent selection using S1, S2 lines would be efficient in increasing levels of resistance both in sorghum and maize. Tolerance should be considered as an important factor in sorghum breeding for borer resistance.

The level of resistance in rice to C. suppressalis is low to moderate and appears to be under polygenic control. A recurrent selection programme using male sterile lines could be effective in improving the level of resistance. No information is available on genetics of resistance to Chilo spp. in sugar-cane.

Several species of Chilo are serious pests of cereal crops. The important species attacking cereals are Chilo agamemnon, C. orichalcociliellus and C. partellus on maize and sorghum; C. auricilius and C. zacconius on sugar-cane, and rice; C. suppressalis on rice; and C. sacchariphagus indicus on sugar-cane. Insects are reared in the laboratory on natural and artificial diets for various purposes, namely for insecticide testing, hormone and pheromone manipulation, biological control, host-plant resistance, etc. Rearing of an insect in the laboratory requires rearing facilities, colony establishment, research and development of rearing techniques, resources, and maintenance of insect quality. All these aspects for rearing major Chilo spp. have been discussed. However, detailed information is available only for C. partellus and C. suppressalis. Techniques used for resistance screening and damage evaluation against spotted stem borer, C. partellus using naturally occurring population and artificial infestation are described.

Laboratory and field assays carried out so far indicate that microsporidian pathogens, especially Nosema spp., may be exploited for the management of the spotted stalk borer Chilo partellus and possibly other Chilo spp. Several formulations have been tested for the application of Nosema spores in the field for borer management. Significantly high levels of control were achieved when the pathogen was sprayed on plants infested with borer larvae, compared with unsprayed plots. Sublethal dosages of Nosema spp. reduced the biological performance of C. partellus, as indicated by reduced fecundity in infected females, high mortality in pre-imagines as well as in the filial generations, and reduced lifespan. There was also a high level of deformity in the surviving adults. Such debilitating factors would subsequently result in a reduction of population levels.

In sugar-cane pests, granulosis viruses have been observed to cause high natural mortalities in C. infuscatellus and C. sacchariphagus. Field infestation has been reduced by the application of the virus. Further, the presence of polyhedrosis viruses in C. partellus, and Chilo iridiscent virus in C. suppressalis, points towards the possibility of using this group of pathogens in Chilo control.