The efficiency and profitability of an integrated pest management system consisting of a phytosanitary survey and threshold interventions (based on levels of insect damage) was tested at the Vallée du Kou irrigated rice scheme in Burkina Faso, for two consecutive crop seasons in 1987. There was a considerable advantage in cost, number of insecticidal applications and yield of a threshold intervention-based system over arbitrary or routine insecticidal application methods. The proposed method is considered to be environmentally friendly.

The permanent mass rearing of rice stem borer, Chilo zacconius in West Africa; rice stem borer, Chilo suppressalis, in Asia and Europe; and sugar-cane stalk borer, Chilo sacchariphagus, in Asia and Indian Ocean was perfected in the laboratory to enable us multiply some parasites such as Apanteles spp., Goniozus procerae, Tetrastichus spp., Trichospilus spp. or the tacbinids, Diatraophaga striatalis and Lixophaga diatraeae.

The principal difficulties appear during mating of several hosts and parasites, development of pyralid young larvae or when it is necessary to protect reared insects or artificial medium against pathogens.

Stem borers are major insect pests of rice in Africa. The utilization of varietal resistance in the management of these pests, has great economic potentials, as it involves no extra cost to the farmer and is also free from environmental hazards. Investigations into the sources of resistance to the African rice striped borer, Chilo zacconius, some possible factors associated with host plant resistance and the benefits derived from growing resistant varieties are briefly reviewed.

Studies were carried out in 1983 to determine the relative abundance and species composition of three lepidopterous stem borers in upland and irrigated rice at Ibadan, southwestern Nigeria. The relationship between irrigated rice crop phenology and the population of the borers and stalk-eyed fly was also studied.

White stem borer, Maliarpha separatella was the predominant species in upland and irrigated rice, followed in upland rice by pink stem borer, Sesamia calamistis, and striped stem borer, Chilo zacconius and in irrigated rice by C. zacconius and S. calamistis. The proportion of M. separatella was higher in irrigated rice than upland. Three population peaks were observed annually in both upland and irrigated rice.

Studies on the relationship between irrigated rice phenology and field population of lepidopterous borers and a dipteran borer showed that the stalk-eyed fly, Diopsis spp., occurred before 20 days after transplanting (DAT) in ITA 212 and continued up to 90 DAT: the peak was observed at 40 DAT. The lepidopterous borers did not appear until 40 DAT and populations peaked at 80 DAT.

Some morphological characters of the rice plant were found to be associated with resistance to the African striped borer, Chilo zacconius Bleszynski. A very low, but negative correlation was recorded between percentages of bored stems and plant height. Positive correlations were recorded between percentages of bored stems and stem diameters, stem thickness, length and width of flag leaves and number of tillers per plant. High silica content in rice plants appeared to be a strong factor in resistance to the striped borer. Negative correlations were recorded between percentages of crude silica content of the plants and percentages of bored stems and number of living larvae per plant. Although each of these factors appeared to contribute to borer resistance, none by itself could be said to be the main cause of such resistance, as some varieties did not conform to some of the characters.

Stem-borer incidence on upland and irrigated rice varieties is compared under natural or artificial infestation, and with simulated damage by sectioning tillers. In the early stages, Diopsids lay more eggs on irrigated varieties, but these are less suitable for the development of Diopsids larvae than upland varieties, whose stems are thicker.

Some varieties of Oryzae glaberrima show a high level of resistance to stem-borers and Hispids. Little difference is noticed for antibiosis of the Oryzae sativa studied, and losses depend on the tolerance of varieties. Irrigated varieties have a better tolerance because of their high tillering, preventing the attack, and of their ability to compensate for early losses by producing new tillers. This compensation does not exist for upland varieties. Their tolerance depends on tillering rate, the ability of infested stems to produce fertile panicles, and the difference in productivity between primary and secondary tillers, the former being more frequently infested. For the same population of stem-borers, losses observed on upland rice are three times lower on tolerant varieties than non-tolerant ones.