A method for steady production of Chilo partellus has been established. An efficient simple and easy method of collection of first instar larvae from incubation chambers has been developed. It has been established that pupae of Chilo partellus can be held at a chilling temperature between 5 and 15°C without any adverse effect on the emergence of adults. This finding has been used in synchronizing the emergence of males and females for mating or longer storage of the pupae.

Studies on the effect of high and low humidities on egg development have shown that low humidities affect the hatchability of Chilo partellus egg but did not effect the actual development of the embryo adversely. It has also been shown that Chilo partellus oviposits best under high humidity.

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.

The advantages and disadvantages of host plant resistance in crop protection are considered. The role of plant resistance as a primary tactic in integrated pest management and its interactions with other tactics, i.e. biological, chemical and cultural are discussed.

The agroecosystem is the basic unit of consideration in the integrated pest management approach. The target crop within this ecological system and its level of susceptibility to insect pest species is of fundamental importance, and can be altered genetically through breeding for pest resistance. The relative level of pest resistance as influenced by pest density, demands a knowledge of pest density and plant damage (yield) relationships. An understanding of these relationships leads to the determination of economic injury levels and subsequently to the establishment of dynamic economic threshold levels. Comparing the economic injury level of insect resistant cultivars to that of susceptible cultivars defines the resistance level and provides the base-line data on which to quantify the effects of other direct control tactics and natural pest density suppressing agents.

Insect resistant sorghums are used as a model to examine the unique values of this tactic as a component in an integrated pest management strategy; the role they play, and how they influence other direct control and support tactics.

The paper stresses the fact that an integrated pest management system is not a new concept leading to a more stable agroecosystem, but was practiced by the farmers for centuries; host-plant resistance is one of its major components. The system was destabilized by the introduction of new sorghum varieties and hybrids not resistant against the major sorghum insect pests like shootfly Atherigona soccata (Rondani); stem borer, Chilo partellus (Swinhoe); midge, Contarinia sorghicola (Coquillet); and headbugs, Calocoris angustatus (Lethiery). In order to balance the agroecosystem again, an integrated insect pest management system for sorghum has to be developed based on traditional pest management practices. These are host-plant resistance, cultural control and biological control. Insecticides should be used only if absolutely necessary. For a better understanding of such a control approach, a summary of the biology and population dynamics of the major insects is given, together with a brief account on the levels and mechanisms of host-plant resistance so far known. Based on this information, the rainfall pattern, plant duration to maturity, time of planting, natural enemies and insecticides, a sorghum based integrated pest management system is proposed for the monsoon and post-monsoon season in which host-plant resistance alone or in combination with the above mentioned control methods could be used.

Among several species of insect pests that attack the millet crop, the earhead caterpillar, Raghuva albipunctella de Joannis and Acigona ignefusalis Hmps., are considered the major pests. The constraints against the successful implementation of an integrated pest management programme of these insects are examined. The relative importance and significance of host plant resistance in such a programme is compared against other modalities.

The use of insecticides is negated by lack of cash value returns, water supply, trained personnel and poor delivery system. Cultural practices, such as the synchronisation of early planting, destruction of harvest residues and end-of-season ploughing, have the potential for reducing carry-over populations. However, the difficulties in their implementation range from farmer education and efficiency to changes in traditional practices and introduction of new labour intensive practices after harvest. While it appears that natural enemies are taking a gradual toll on R. albipunctella, they appear inefficient in controlling A. ignefusalis. A range of plant characters have been identified: tillering in certain varieties as a form of tolerance to borers; maturity cycles that result in escape (pseudo-resistance) from Raghuva infestation, hairiness in relation to preference for oviposition and head compactness in deterring larval penetration into millet heads. Most of these characters are common in landrace types. The real problem appears to be one of incorporating and utilising the identified resistance into germplasm sources which possess other desirable agronomic characters that the farmer requires. This implies multi-disciplinary effort which is the basis for integrated pest management. In most of Africa, and in the Sahel in particular, this basis is remotely present.

The origin of African rice, Oryza glaberrima Steud and Asian rice, O. saliva L., in West Africa is briefly reviewed. Major pests of rice in this region have been listed and the present status of crop protection with reference to rice is discussed. Major constraints to utilization of varietal resistance as a component in crop protection are mainly research-related. The need for manpower development, provision of adequate facilities, standardization of techniques as well as greater emphasis on studies on varietal resistance are highlighted.

Distinct differences in Panonychus ulmi population densities on various apple cultivars have been observed under natural field infestations. Various laboratory techniques may be used to determine the differences in susceptibility or resistance to P. ulmi of different apple cultivars. The lowest variation in P. ulmi behaviour, and fecundity between replications was observed for females reared on leaf discs 20–25 mm in diameter and for females reared in the small plastic cages placed on the leaves of potted young apple trees. The leaves used for bioassays should be collected from the same part of the trees. The density of P. ulmi populations and their fecundity should be observed on leaves growing on short spurs. Preconditioning P. ulmi on various cultivars did not influence the female's fecundity on the new plants. There is no individual, singly-acting mechanism responsible for the moderate resistance of apples to P. ulmi. The resistance is caused by a number of morphological, anatomical and biochemical leaf properties, expressed differently in different cultivars.