Various insect pests, of which stemborers are the most widely distributed and damaging, affect about 30 out of the 35 million hectares planted with maize in developing countries. Chemical control, biological control; cultural methods and host plant resistance constitute the four general approaches to stemborer control. The use of stemborer-resistant maize increases farming efficiency by both reducing yield losses from stemborer damage and reducing or eliminating the cost of insecticides and other inputs. In the past, CIMMYT followed conventional breeding methods to develop germplasm resistant to stemborers and molecular technology, quantitative trait loci (QTL) in marker-assisted selection (MAS) to select for improved stemborer resistance in elite lines. More recently, CIMMYT has developed the capacity to produce transgenic maize with resistance factor(s) derived from genes that encode delta-endotoxins derived from the soil bacterium Bacillus thuringiensis (Bt). A sub-tropical source population with multiple borer resistance (MBR population) was developed by recombination and recurrent selection under infestation with four stemborer species. Marker-assisted selection is being used in two African countries to promote the transfer of resistance into elite and adapted germplasm. The Insect Resistant Maize for Africa (IRMA) project is pursuing the transfer of Bt-based resistance to adapted maize germplasm, initially in Kenya, but later to other interested African countries. CIMMYT's varietal release strategy is to pyramid Bt genes into maize populations with existing multigenic pest resistance, in order to enhance both the levels and durability of plant resistance to maize pests. This paper discusses the various approaches used at CIMMYT to develop stemborer-resistant maize germplasm.

Surveys were conducted to determine the species composition of stemborers and their natural enemies in maize and sorghum in 1999 and 2000 in eastern, northern, southern and western Ethiopia. The six species of stemborers found attacking maize and sorghum were Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), Busseola fusca Fuller, Sesamia calamistis Hampson (Lepidoptera: Noctuidae), S. nonagrioides botanephaga Tarns & Bowden (Lepidoptera: Noctuidae), Rhynchaenus niger (Horn) (Coleoptera: Rhynchophoridae) and Pissodes dubious (Ström) (Coleoptera: Rhynchophoridae). Twenty species of primary parasitoids of eggs, larvae and pupae of Ch. partellus, B. fusca and S. calamistis were recorded. Other natural enemies, including predators, fungi and nematodes, were also found. Cotesia flavipes Cameron (Hymenoptera: Braconidae) was the dominant and the most widely distributed parasitoid of stemborers in Ethiopia, and was reared from field-collected Ch. partellus, B. fusca and S. calamistis.

Studies were conducted in two districts of eastern Uganda from 1997 to 1999 to introduce and monitor the establishment of an exotic parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae), for the control of the stemborer Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), and also to determine the stemborer species complex in maize and sorghum. The study confirmed the presence of four important stemborers, two pyralids Ch. partellus and Eldana saccharina Walker and two noctuids, Busseola fusca Fuller and Sesamia calamistis Hampson. Chilo partellus was dominant, constituting 53–88% of stemborers four d followed by B. fusca at 8–37 %. The most abundant local parasitoid was the larval parasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae). The pupal parasitoids Pediobius furvus Gahan (Hymenoptera: Eulophidae) and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) were also recorded. Parasitism of Co. sesamiae on Ch. partellus ranged between 0 and 13.1 %. The introduced Co. flavipes was recovered from all sites in four consecutive seasons (between 1998 and 1999) causing parasitism of between 4 and 32.9 % on Ch. partellus. Cotesia flavipes was also recovered from the indigenous stemborers B. fusca and S. calamistis. This study indicates that Co. flavipes has established in eastern Uganda.

During foraging, parasitoids of insect herbivores are aided by chemical compounds generally termed ‘infochemicals’, to locate their hosts. The origin of the infochemicals varies; they may be derived from the herbivore itself or activities related to the biology of the herbivore, the host plant, or from interactions between the plant and the herbivore. This paper reviews the status of research in this area, and presents an account of the infochemicals used by African stemborer parasitoids during foraging, as well as recommending possible areas for further investigation. The information generated has potential for application in behaviour modification of parasitoids species in biological control programmes.

The stemborers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) cause the highest economic damage to maize and sorghum in Zimbabwe. A number of studies on stemborer bioecology and management in Zimbabwe have been conducted, but most are still incomplete. The more important of these are studies on life history, incidence and distribution patterns, host plants, yield losses, chemical control, cultural control, host plant resistance, the use of sex pheromones, and biological control. These are discussed here in detail, and areas where further research is needed are pointed out. As part of an integrated strategy for managing stemborers in Zimbabwe, an exotic braconid larval parasitoid, Cotesia flavipes Cameron, has been released in the lowveld area and prospects for its establishment appear to be good. However, this establishment might be curtailed mainly by the inability of Co. flavipes to adapt to the seasonal carryover mechanisms utilised by the indigenous Cotesia sesamiae (Cameron).

The development, life table and intrinsic rate of natural increase of the reduviid predator Rhynocoris fuscipes (Fabricius) on Spodoptera litura Fab., Earias vittella Fab. and Corcyra cephalonica Stainton under laboratory conditions were constructed. Fecundity, longevity and minimum developmental period of the predator were dependent on the prey diet and decreased in the order: S. litura, E. vittella and C. cephalonica. The mean number of female progeny produced over the entire period (the gross reproductive rate) was 43.0, 37.5 and 32.5 on S. litura, E. vittella and C. cephalonica respectively. The net reproductive rate (Ro), intrinsic rate of increase (rc) and weekly multiplication rate were also highest on S. litura followed by E. vittella and C. cephalonica.

Cowpea, Vigna unguiculata (Walp) and beans, Phaseolus vulgaris are attacked by several insect pests worldwide. The pests include economically important borers, the control of which often requires the use of more than one tactic. In Africa, the major borer species of cowpea is Manica vitrata Fab. (syn. M. testulalis [Geyer]); in Southeast Asia and eastern Africa the beanfly or bean stem maggot complex, Ophiomyia spp., is important on beans. The bean borer, Etiella zinckenella (Treitschke), is also of considerable importance in Asia. In South America Epinotia apotema (Wals) and Cydia fabivora (Meyrick) are the most important borers on beans, while Helicoverpa armigera (Hïbner) and M. vitrata to a lesser degree are important on beans in some parts of Africa. Presently, only chemical control provides complete protection against crop borers, but despite its usually favourable cost-to-benefit ratio, insecticide use is not a sustainable option. Other tactics such as cultural control, host plant resistance and the use of beneficial organisms are more dependable in the long-term. They form the core of the new vision for environmentally friendly pest management, or bio-intensive pest management, which minimises the use of synthetic insecticides. In recent times, research efforts directed at these measures have been intensified. This paper discusses the various interventions and presents different IPM models on how they can be combined to optimise the control of borers. Suggestions are made on the future outlook of IPM on cowpea and beans.

Several strains of Hyphomycetes fungi were assayed in the laboratory to determine their pathogenicity against second instar Chilo partellus Swinhoe larvae and fifth–sixth instar Busseola fusca Fuller larvae. Pathogenic activity to both stem borers was demonstrated with Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin. B. bassiana isolates caused mortality of 3–100% of mortality in C. partellus larvae, and 30–84% in B.fusca. Strains of M.anisopliae showed a high level of virulence for both insect pests, causing mortality levels of 65–100%. Development of fungal infection appeared to take longer in B. fusca larvae (LT50 of 6.2–13.2 days) than in C. partellus (LT50 of 1.9–5.4 days). B. bassiana isolate ICIPE 4, and M. anisopliae isolates ICIPE 18 and 30, which were effective against both stem borers, outperformed the other pathogens tested. They appear to have potential for use asmicrobial agents in the control of C. partellus and B. fusca.