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.

A number of resistance sources have been identified against two major pests of sorghum, viz the sorghum shootfly, Atherigona soccata Rondani, and the stem-borer, Chilo partellus (Swinhoe). These identified sources of resistance were generally tall, late maturing and poor yielders. Two of these identified sources of resistance, viz. BP 53 and M 35-I, have been utilized in the breeding programme, by crossing with dwarf exotic types, which are highly susceptible to both the pests, but are agronomically desirable varieties. The crosses thus obtained were screened for their reaction to the two pests. An extensive screening programme was carried out under heavy levels of shootfly and stem-borer infestation from 1968 to 1980, which resulted in the identification of nine advanced generation derivatives possessing moderate to high levels of resistance to both shootfly and stem-borer as well as desirable agronomic characters.

The derivatives with M 35-I, as one of the parents showed more resistance to shootfly as compared to derivatives with BP 53, as one of the parents. However, in the case of resistance to stem-borer, the reverse was true.

Insect pests are major yield reducers in sorghum under traditional farming practices in Africa. The use of resistant varieties in an integrated pest management scheme provides the most cost effective and practical means of sorghum insect control. Corneous grain sorghums are more weevil resistant than their softer endosperm counterparts. A wide range of sources of resistance to shootfiy, stem-borer and greenbug are known. Breeding for resistance to sorghum insects has been practised with varying degrees of success. Greenbug resistance breeding in sorghum has been successful in the U.S.A. Stem-borers are perhaps the most serious group of sorghum insects in Eastern Africa and further efforts are needed in breeding for resistance to these pests. In an effective pest resistance breeding work, the breeder and the entomologist must work as a team to make the fastest possible progress. Where several pests are of concern in an area, genotypes with multiple resistance in good agronomic backgrounds are needed.

About 20 species of borers are rice pests. Of these, five—yellow borer, striped borer, white borer, dark-headed borer, and pink borer—are of economic importance. Yellow borer and striped borer occur most widely in Asia and cause serious yield losses.

Varietal resistance to these two species has been investigated during the last 30 years. Field and greenhouse screening techniques have been developed and numerous germplasm entries have been evaluated for resistance. Several hundred varieties with low to moderate levels of resistance have been identified. Except for several wild species of Oryza, germplasm with a high level of resistance has not been found.

Information available to date indicates that the resistance is under polygenic control. Moderate levels of resistance from several donor parents have been incorporated into improved varieties. Some of these moderately resistant varieties, for example, IR20, IR36, IR50, Ratna and Chandina, are widely grown and play an important role in integrated pest management programs for stem-borer control. Efforts to develop cultivars with levels of resistance higher than presently grown varieties are under way using the diallel selective mating system and the male sterile facilitated recurrent selection schemes.

Orseolia oryzae, the rice gall midge, is a major pest of rice in many areas of tropical Asia and is becoming an important pest in Africa. A chronological review of the progress made in various national programmes on varietal resistance, sources of resistance and breeding for resistance is given. Many resistant varieties have been identified and have been utilized in breeding programmes to develop high yielding varieties with multiple resistance to the gall midge and other insect pests and diseases. Mechanisms and inheritance of resistance in rice varieties are discussed. Rice varieties resistant in various countries and sources of resistance used in breeding programmes are listed. Biotype variations in different countries and within the countries are revealed, and a preliminary classification of gall midge biotypes based on varietal reactions is proposed.