Three species of Chilo, namely C. auricilius, C. suppressalis, and C. polychrysus are predominant in Asia; and the other three, C. zacconius, C. partellus, and C. diffusilineus are predominant in Africa on rice crop. Various screening methods to identify resistance donors in cultivated as well as wild rices have been used over the last 30 years. The level of resistance in available donors of cultivated species is moderate, except in some accessions of Oryza nivara/O. rufipogon, O. officinalis, O. brachyartha and O. minuta. Genetics of resistance is complex as appears from the review. Efforts to incorporate the resistance into new developing breeding lines have been sporadic and discontinuous in African countries. At IRRI and in many Asian countries, systematic approaches have been undertaken. Once donors with superior levels of resistance become available, systematic breeding approach has to be made with the help of multidisciplinary teams at suitable test sites. African breeding programmes need close linkage with IRRI's stem borer programme and International Rice Stem Borer Nursery.

Trials using deltamethrin impregnated odour-baited targets for control of tsetse, have been running in Galana Ranch on the coastal hitherland since 1986. In July 1988, a similar trial was started in Lambwe Valley, Western Kenya. Glossina pallidipes is the sole vector in the valley and is present in very high densities.

In Galana Ranch trial, octenol and acetone are used as odours while in Lambwe Valley, natural cow urine is used in addition to acetone and octenol. Tsetse population densities were assessed weekly for 3 weeks, before deployment of targets and thereafter at monthly intervals. A herd of cattle is used to monitor the effect of the control measures on disease incidence.

On Galana Ranch, the block where the initial trial began has remained free of G. pallidipes for a period of 3 years. In a period of 9 months in the second year of the trial, the berenil index in a herd of cattle was 0.07 in the controlled area compared to 2.5 in the uncontrolled area.

In Lambwe Valley a 99.9% reduction in trap catches has been observed in most parts of the park at the end of the first year. The berenil index in the cattle has dropped from 6.3 to 0 and there is a general improvementin the health of the animals. Observations are continuing at both sites.

Riverine tsetse, which are vectors of human and animal vectors, are very difficult to control because of the specific nature of their habitat and behaviour. The problem, however, is not technical, because nowadays entomologists have at their disposal a wide range of efficient methods to eradicate them. The problem is therefore practical, and it is related to the way in which these methods are used.

In fact, the entomologist is faced with several intractable problems that reduce his scope of action. First of all, because he has to pay due regard to the environment, he is obliged to refrain from taking any action that may be fatal for the tsetse, but harmful for the environment such as cutting down woody, scrub and shrub vegetation, setting bush fires, etc. Furthermore, he is not allowed to tamper with wildlife which is the nutritional source of the tsetse, but is also an important source of foreign exchange through tourism. He also must respect the non-target fauna, especially the aquatic fauna, with the result that this limits: (1) the choice of pesticides that can be used in one way or the other, affecting the chain in the biological cycle, invertebrates, fish, birds, mammals and (2) the method of application of chemical, because he cannot use residual sprays or aerial aerosols everywhere.

The entomologist must also take into account economic considerations. The world economic crisis has considerably reduced the availability of potential sources of donor funds, and most African countries afflicted by sleeping sickness and animal trypanosomiasis cannot individually undertake large-scale eradication campaigns for lack of funds, adequate equipment and trained manpower. Using aeroplanes or hordes of workers is therefore out of question. Similarly, controlling the tsetse through the use of sterile male release technique, which is a complementary control method to attain the 0 density, seems now to be unachievable because of the huge investments that are required.

Finally, many scientists, economists and ecologists have recently begun to wonder if controlling the tsetse is after all a good solution, since their disappearance would lead to the overexploitationofthe land freed, resulting in the destruction of the vegetation and bio-climatic changes and finally total desertification. The challenge therefore is how to control the tsetse under these conditions.

The use of traps seems to be a good solution. Experiments conducted in Africa (and since the discovery of certain olfactive attractants) have shown that it is effective, safe for the environment, easy to use, and especially very cheap, when it is used by the rural communities. But even with trapping, a number of questions are being asked: Is it better to kill the tsetse than to sterilize it? Is impregnating it with an insecticide indispensable? Is there no risk of selecting a “trap resistant strain” of tsetse? Can the use of traps lead to eradication?

In fact, in most cases, eradication is wishful thinking and controlling the fly is the only realistic thing to do; the entomologist has to control, but cheaply and with a less harmful technique. Besides, because of its numerous qualities, trapping is the only method that can be used nowadays as long as it is used wisely.

Host-plant resistance plays an important role in the insect-pest management either alone or in combination with other control methods. A number of sorghum genotypes showing varying levels of resistance to spotted stem borer, Chilo partellus Swinhoe have been identified using natural and artificial infestations. Major resistance mechanisms are antibiosis and tolerance, though some genotypes exhibit ovipositional non-preferences. There have been a number of factors involved in spotted stem borer resistance; a resistant genotype possesses either one or a combination of these traits. Progress has been made in developing borer resistant breeding lines with moderate yield and acceptable grain quality. Borer resistance is a quantitatively inherited trait governed by additive and non-additive genes. Epistatic gene effects are more pronounced under artificial borer infestation. Cytoplasmic effects appear to be present.

Chilo species are the most important stem borers of sugar-cane. They cause heavy losses to sugar-cane crop and continue to suppress yield in the sugar industry. The control of these borer species through insecticides has been difficult as the damaging larvae spend most of their life-cycle within the cane plant. The breeding of borer resistant varieties is an ideal approach for controlling the damage as it does not cost the grower anything extra, is effective at all levels of pest infestation and its effects are cumulative and long lasting in reducing the pest population. Many plant characters such as leaf surface, rind hardness, leaf sheath tightness, fibre content, stalk pith and diameter and plant vigour have been associated with borer resistance. In sugar-cane breeding, the inclusion of borer resistance characters, in addition to many other agronomic characters required of a commercial variety, is rather difficult due to the segregating nature of this plant. Therefore, it is better to use, as parent varieties the few varieties showing marked resistance without knowing the actual reasons of resistance. The joint efforts of sugar-cane breeders and entomologists in production and selection of a large number of seedlings for desired characters can help to solve this problem to a greater extent.

Six genera of bacteria: Serratia, Providencia, Enterobacter, Aeromonas, Cedecea and Bacillus were isolated from field-collected G. pallidipes. Four genera: Serratia, Providencia, Enterobacter and Aeromonas were isolated from insectary-reared Glossina morsitans morsitans. All bacteria except, Bacillus spp. and Providencia alcalifaciens were pathogenic for teneral G. m. morsitans. Bacteria isolated from insectary-reared tsetse were more pathogenic than those isolated from the field. Fungi of three genera were also isolated from field-collected adult G. pallidipes, Penicillium, Aspergillus and Fusarium. Five genera, Aspergillus, Penicillium, Rhizopus, Mucor and Trichoderma were isolated from field-collected G. pallidipes pupae. The fungi, however, were only mildly pathogenic for adult tsetse and were not pathogenic for pupae.

A spreadsheet computer model of the benefits and costs of tsetse control has been developed. It aims to provide a sufficiently standardized framework for setting these out so that widely different situations can be compared. For this purpose, the main variables are grouped into four categories: cattle production system, disease impact on productivity, tsetse control costs and stocking density (represented by cattle in the area before control and those transferred into the area subsequently). The model covers direct benefit due to changes in productivity resulting from reduced mortality, morbidity and drug use and indirect benefits due to transfers of cattle into the area and the increased use of work oxen. A series of runs of the model based on a cattle production system oriented towards draught power production is used to illustrate how the model can be used to define the conditions under which tsetse control is likely to be economically viable.

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.

The main reason for tsetse eradication, in the past, has been to remove the restraint of disease on cattle production. It is now argued, that the major restraint is not disease but poor land made worse by overgrazing.An association between overgrazing and drought is recognized in South America, Central America and Australia. In Africa there is strong, but circumstantial evidence that overgrazing may be linked to climatic change. Tsetse populations may in the past have been a major restraint on overgrazing but with new advances in technology it is now possible for such populations to be “managed” in order to protect vulnerable rangelands.Such a concept would mean changes in the attitude of society to tsetse which should come to regard them as a potential asset rather than as a liability.

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.

The control of pest populations through the manipulation of their genetic component or mechanism of inheritance is becoming increasingly important. Two of the most promising genetic methods for the control of iepidopteran insects are inherited or F1 and hybrid sterility.

To induce F1 sterility in C. partellus, male pupae were irradiated with various doses of gamma radiation (0–15 krad) and emerging adults of normal appearance were used in crosses with normal females. The F1 progeny were reared on artificial diet and the resulting adult males were crossed with unirradiated females to give F2, the process being repeated until F5 progeny were obtained. For each generation lifespan of males, oviposition, egg hatchability and sex ratio were carefully recorded. The results showed that females mated with irradiated males oviposited significantly fewer eggs than normal and that this phenomenon was perpetuated over several generations. Hatchability of eggs laid by females mated to irradiated males or male progeny was significantly lower than that of the controls and sex ratio was distorted slightly in favour of males in all generations observed. The lower oviposition, lower egg hatch, distortion of sex ratio in favour of males and the apparent persistence of sterility over several generations offer the potential of inherited sterility for the control of C. partellus.

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.