Stemborers are a major constraint to the production of rice in the Kou Valley, Burkina Faso. Biological control is a good alternative to the use of agrochemicals that are harmful to human and animal health, and the environment. A survey of natural enemies of stemborers was conducted during the 2014 rice-cropping season across three transplanting periods (P1, P2 and P3). Plant and insect samples were collected by mowing and trapping at weekly intervals until harvest, starting 21 days after transplanting, and examined microscopically. Immature stages of the parasitized stemborers were reared to maturity for a positive identification of the parasitoids. Three genera of stemborers were identified: Chilo (Lepidoptera: Pyralidae), Maliarpha (Lepidoptera: Pyralidae) and Sesamia (Lepidoptera: Noctuidae). The Chilo genus was the most important with an average percentage of 41.4% of the pre-imaginal population in P2 followed by Marliarpha (1.1%) and Sesamia (0%). A total of 15 hymenopteran parasitoid species that included nine genera and seven families were identified. All the parasitoids were associated with Chilo and only two of the species parasitized Maliarpha. The most frequent parasitoids encountered were Bracon testacerofatus, Goniozus indicus, Dolichogenidea oryzae and Bracon spp. A total of 28 predator species were recorded from 22 genera, 6 orders and 15 families. Leucauge sp., Agriocnemis sp., Lycosa pseudoannulata and Lycosa sp. were the most important predators with frequencies reaching 15% of the arthropods caught in some fields. These results will be employed to develop a sustainable system to manage rice stemborers.

Cotesia flavipes Cameron (Hymenoptera: Braconidae) was introduced in Uganda in 1998 for the biological control of the old association cereal stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). However there is little information on whether this parasitoid will attack new association Lepidoptera, which in turn may have implications on its efficacy on Ch. partellus. This study investigated the incidence of introduced Co. flavipes on Ch. partellus, and new association lepidopteran species and associated effects on its efficacy. Parasitism levels for Co. flavipes in several locations varied between 13.7–34.8% and 1.5–18.8% on Ch. partellus and new association hosts, respectively. Implications for biological control of stemborers in Uganda are discussed.

Genetically-engineered (GE) crops such as those expressing insecticidal Bacillus thuringiensis (Bt) toxin genes have the potential to greatly reduce the use of broad spectrum insecticides and increase crop productivity. However, development of resistance by the target insect species is an important consideration in the deployment of this strategy. In areas where GE crops are deployed on a large scale, current resistance management strategies rely on a ‘refuge strategy’, comprising the incorporation of a certain proportion of non-GE plants in the agro-ecosystems, to conserve susceptible individuals of the target pests. In the USA, simulation models indicate that at least 20% of the crop should be non-Bt plants. In Africa, the target lepidopteran stemborers attack a wide range of wild grass species as well as cultivated cereal crops. Wild grasses generally occur in the vicinity of maize and other cereal fields, and may provide a refuge if GE crops are in the farming systems. To assess the quality of these grasses as refuges, it is critical to obtain information about their size and spatial distribution. In this study, we have assessed the abundance and diversity of alternative refuge of stemborers, mainly wild grasses occurring in the proximity of maize fields, in Trans-Nzoia district, one of the most important maize growing areas in Kenya. The proportion of wild host plants relative to maize was found to decline from 100% during the non-cropping season to <8% during the maize-growing season. The Shannon-Weaver diversity index indicated high variation in the diversity of wild hosts of stemborers between agro-ecological zones in the district. The results of this study are discussed in light of the possible role that wild host plant species might play in stemborer resistance management following the introduction of Bt maize.

Three hundred and ninety-two maize fields in the southern arable zone of Kenya were sampled for lepidopteran cereal stemborers from 1996–2000. Chilo partellus (Swinhoe) was the most abundant stemborer, and was found at all locations with elevations below 1500 m, and at some locations between 1500 and 2300 m. The highest density of C. partellus was in the semi-arid ecological zone of eastern Kenya. Chilo orichalcociliellus (Strand) was found in the lowland southern coastal area, and a few inland sites on the border of Tanzania in southeastern Kenya. Busseola fusca Fuller was dominant in highland areas. In the Lake Victoria Basin, which has an elevation of about 1100 m, B. fusca was dominant at some sites, but overall, C. partellus was more abundant. Sesamia calamistis Hampson was present at all elevations and all locations, but typically at low densities. Eldana saccharina (Walker) was found in two-thirds of the fields sampled in the Lake Victoria Basin. These results are compared with the distributions of the various stemborers in the 1950s to 1960s, as reported in the literature.

Surveys of the cereal stemborers and their natural enemies in Zambia were initiated in 1997. The surveys verified the presence of three stemborer species on maize, sorghum and pearl millet. These were the maize stalk borer, Busseola fusca Fuller (Lepidoptera: Noctuidae), the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and the African pink borer, Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Occasionally, the sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) was also recovered especially around areas near the sugarcane plantation at Mazabuka, Southern province. Chilo partellus was the predominant stemborer in region I (areas with less than 600 mm of rainfall per annum). Three ‘hot spot’ areas, namely Luangwa, Buleya Malima and Kalobolelwa, were identified based on the abundance of Ch. partellus. The exotic parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae) was released in the three areas for the control of Ch. partellus. However, post-release surveys in these areas have not revealed any recoveries of Co. flavipes. Three indigenous natural enemies, namely Cotesia sp., Dentichasmias sp. and Dolichogenidea sp. emerged from the field-collected larvae.

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.

Field surveys carried out in Mozambique showed that two indigenous cereal stemborers, Busseola fusca Fuller (Lepidoptera: Noctuidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and one exotic stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), are the main pests of maize and sorghum in the country. Busseola fusca was abundant at high altitudes (> 800 m) and Ch. partellus was abundant at low altitudes (< 800 m). Sesamia calamistis occurred at all elevations but in low numbers. Of the three stemborers, Ch. partellus was the most widespread and abundant pest of maize followed by B. fusca. Therefore, a programme was initiated to introduce the exotic parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae) to increase natural suppression of Ch. partellus populations. Cotesia flavipes was introduced into southern Mozambique for the first time in November 1996. Additional releases were subsequently carried out in several places in southern and central Moz imbique from 1998–2000. The parasitoid was recovered from all localities sampled 1 to 3 years after its introduction, indicating that this exotic parasitoid had established in the southern and central regions of Mozambique.

Maize is the principal food and cash crop for millions of people in the predominantly mixed crop-livestock farming systems in Kenya. Stemborers and striga (Striga hermonthica) are major constraints to increased maize production in eastern Africa. An intercropping and trap crop system has been developed, using a ‘push-pull’ strategy, for the control of stemborers in small scale maize farming systems. The ‘push-pull’ strategy involves trapping stemborers on highly susceptible trap plants (pull) and driving them away from the crop using repellent intercrops (push). Napier grass (Pennisetum purpureum Schumach) and Sudan grass (Sorghum vulgare sudanense Stapf.) are used as trap plants, whereas molasses grass (Melinis minutiflora Beauv.) and two species of desmodium (Desmodium uncinatum Jacq. and Desmodium intortum Urb.) repel ovipositing stemborers. The integrated ‘push-pull’ strategies were shown to increase parasitism of stemborers through attraction of parasitoids to one of the intercrops, molasses grass. The leguminous intercrop, silver leaf desmodium, drastically reduced damage to maize by the parasitic weed, striga. This aspect was further investigated and developed for integration with stemborer control. On-farm trials with farmers in Kenya have shown significant yield increases in maize farming.

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.

Cotesia flavipes Cameron (Hymenoptera: Braconidae), a gregarious larval endoparasitoid of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and other stemborers in the Indo-Australian region, was released in Mozambique for the first time in 1996. Before its release, countrywide surveys on stemborers and their natural enemies were conducted in several places. However, all led to the same conclusion: that Ch. partellus was the most abundant stemborer at the majority of locations, and that the rate of larval parasitism was very low (< 5 %). To evaluate the effect of stemborer species composition on the establishment of Co. flavipes, two releases were made at two agroecologically different sites during the 1998/1999 and 1999/2000 growing seasons. Cotesia flavipes was recovered from all the three stemborer species found at each site during the season of release and a year later. However, the rates of parasitism were very low, ranging from 0.6 to 1.9 % on Ch. partellus, 3.2 % on Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and 2.6 % on Busseola fusca Fuller (Lepidoptera: Noctuidae). The native natural enemy, Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) was the most common larval parasitoid at the two sites. The recoveries of Co. flavipes during the release period and a year later indicate that this exotic parasitoid has become established at the two locations in the southern and central regipns of Mozambique, in spite of differences in stemborer species composition. However, it is too early to evaluate the impact of Co. flavipes on the stemborer populations.

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 stemborers Busseola fusca (Lepidoptera: Noctuidae) and Chilo partellus (Lepidoptera: Crambidae) are important pests of maize and sorghum in South Africa. A habitat management system for these pests is being developed in the Northern Province of South Africa. This management system is similar to the one used in eastern Africa, where host and non-host plants of stemborers are used to repel moths away from the main crop and attract them to highly attractive trap plants. To identify possible trap crops, a survey of wild host plants of stemborers was undertaken in the Northern Province of South Africa and several new host plants were recorded. As a possible trap crop for stemborers, various Napier grass (Pennisetum purpureum) varieties were evaluated for oviposition preference by Ch. partellus moths and subsequent larval survival on those varieties. Few larvae survived longer than 15 days after inoculation onto Napier grass plants. A survey was conducted of farming practices that would affect the adoption of habitat management strategies. The high usage of tractors for ploughing may have a negative effect on adoption of perennial intercrops in a habitat management system. The common practice of free grazing animals also reduced the fodder value and benefit of trap crops. The value of Napier grass does not only lie in its use as trap crop but also as a measure to limit soil erosion and as animal feed.

A field survey on maize stemborers, stemborer damage, maize plant physical conditions, and maize yield was conducted in eastern Kenya under natural conditions. Chilo partellus was the dominant stemborer accounting for 89.5 % of all borers. Stemborer damage greatly reduced maize yield, with tunnel lengths greater than 20 cm causing a 40 % reduction of potential yield. A 33 % yield loss was found in plants with more than one stemborer exit hole. Each stemborer (at harvest time) was correlated with a 8–10 % yield loss. Good plant physical characteristics significantly increased grain yield. Principle component analysis showed that stemborer damage, plant height and stem diameter were key factors affecting maize grain yield. Regression analysis indicated that one centimetre of stemborer tunnel reduced yield by 3 g/plant. Multiple regression analysis implied a 13.3 ± 1.5 g yield loss (8–10 % of potential yield) due to the damage of a single stemborer. Comparison with average yields in the study area suggested that our results were representative of losses on farmers' fields.

A survey among 240 resource-poor farmers at the Kenya coast indicated that insect pests were considered to be the main production constraint. Over 70% of respondents mentioned stemborers to be the most important insect pest. Unlike the eggs and adults, stemborer larvae and pupae were frequently seen by farmers. Alternative gramineous host plants for pests were common near maize fields and were often not destroyed until after the first rains. Nearly all farmers left dry stems and stubble in the field after harvest. Farmers knew of many methods for controlling stemborers, but only 32 and 56% of farmers in Kilifi and Kwale Districts, respectively, used any of the methods. Chemical control was the most popular control method, being applied regularly by 19 and 38% of farmers in Kilifi and Kwale Districts, respectively. Traditional methods and cultural control methods were seldom used. Approximately 50% of farmers had heard of beneficial insects, with farmers collectively mentioning 17 predators of stemborers. Cocoons of the parasitoids Cotesia flavipes, released in a biological control programme in the study area in 1993, and the indigenous Cotesia sesamiae had been seen by 33% of respondents, but none knew what these were. The results of the present study stress the need to educate farmers about the biology and ecology of stemborers and the role of natural enemies. Also, after effective control methods suitable for resource-poor farmers have been identified, both groups should be trained in pest management methods, for example through the Farmers Field School approach.

The effect of potassium application to maize plants on the development, survival and fecundity as well as larval and pupal weight of Sesamia calamistis and Eldana saccharina were studied in the laboratory. Six different potassium treatments corresponding to 0, 30, 60, 60, 90, 120 and 150 kg K2O/ha were used. Potassium had no influence on larval and pupal developmental time or longevity of adult S. calamistis. The highest larval mortality was observed at 0 and at 150 kg K2O/ha. Increased doses (> 60 kg K2O/ha.) tended to reduce pupal survival. The lowest pupal weight was obtained at 150 kg/ha whereas fecundity was negatively related with potassium. The highest values of intrinsic rate of increase (rm) and net reproductive rate (Ro) were obtained with 60 kg K2O/ha and lowest with 150 kg K2O/ha. For E. saccharina, potassium had no significant effect on larval and pupal developmental time, larval survival, and pupal weight. The highest larval weight, pupal survival and fecundity as well as rm and Ro values were observed at 90 kg K2O/ha.

A ‘rice garden’ with monthly plantings of rice was established in an irrigated lowland area in April 1993 and continued for 3 years. Populations of the most common insects, the stalk-eyed flies, Diopsis spp., and the green leafhoppers, Nephotettix spp., and spiders and stemborer damage varied distinctly in relation to month of transplanting. Arthropod populations also exhibited distinct patterns in relation to crop growth stage. Grain yields varied with month of transplanting but there was no distinct trend from one year to the next. This study indicated that continuous cropping of the same fields over a 3-year period did not result in a build-up of insect pests or a decline in grain yield.

A 2-year study was conducted to determine the abundance of rice arthropods as affected by weeding regimes and toposequence sites, from upland to lowland, in an inland valley in Côte d'Ivoire, West Africa. Toposequence site had an effect on insect populations. Most insects were found in the moist, lower portion of the slope (hydromorphic or phreatic zone) and in the valley bottom (irrigated lowland). Among these were the white leafhoppers Cofana spectra and C. unimaciilata (Hemiptera: Cicadellidae), the green leafhoppers Nephotettix spp. (Hemiptera: Cicadellidae), and the diopsids Diopsis longicornis and D. apicalis (Diptera: Diopsidae). Stemborer damage was generally most severe in the lowland ecology. Weed dry weights and weed species composition were affected by toposequence site. Cyperns difformis L. was most abundant in the lowland and Digitarla horizontalis Willd. in the upland sites. Weeding regime had an effect on the abundance of insect pests and natural enemies (spiders and damselflies) and on the extent of stemborer damage, the effect varying with toposequence site. Implications of the results for the integrated management of weeds and insects are discussed.

Lepidopteran stemborers are major limiting factors in the production of maize and sorghum in Africa and Asia. Host-plant resistance and biological control are important components of an IPM programme and can effectively maintain pest populations below economic threshold levels, especially in low-input subsistence farming systems. When damaged by herbivores, plants produce allelochemicals which can attract natural enemies of the pest. These volatiles occur systematically throughout the plant and are different from those emitted in response to mechanical damage. We report evidence of plant volatiles-mediated differential reaction of parasitoid activity to sorghum genotypes. These volatiles could have a positive impact on the efficacy of stemborer parasitoids, leading to increased host finding or increased searching efficiency, thereby enhancing the suppression of stemborer populations. In a single-season case study, parasitoid activity was higher in stemborer-resistant genotypes than in susceptible ones and varied with crop age. Knowledge of such interactions should be explored and intensified by plant breeders and chemical ecologiste aiming at producing plant materials possessing appreciable levels of resistance to stemborers and able to encourage natural enemy activity in cereal-based ecosystems.