Since taking over as Editor-in-Chief of Insect Science and its Application with Volume 16, major changes have been undertaken by the editorial and production teams to improve the journal's quality, presentation, format, timeliness and overall coverage. In Volume 17, these changes are more visible, with the new cover design and layout. In terms of quality, the relevance and originality of the content of the accepted articles is being constantly improved. Inevitably, this has led to increased rejection of papers which no longer meet the new standards. On the editorial side, we have set in place a broadened team of scientific editors and given additional training to existing staff. The process of regionalising the editorial activities in Latin America, Asia and Africa is also progressing and we hope to have the regional offices in place in the not too distant future.

Several species of stemborers attack sorghum and pearl millet in Africa and Asia. The commonest species on sorghum are Chilo partellus (Swinhoe) and Busseola fusca (Fuller) and on pearl millet, Contesta ignefusalis (Hampson). This paper discusses control options and the extent to which farmer perceptions of stemborers and associated crop losses have been considered. Examples of research aimed at developing IPM strategies are presented in the context of their impact or lack of it, on the farming community. Research efforts have traditionally focused on the development of resistant cultivare and only recently are they being targeted towards a combination with cultural and biological tactics. Conventional breeding procedures have not produced adequate levels of resistance to stemborers and natural enemies are not effective in regulating borer populations. The prospects of applied biological control and improved intercropping configurations are discussed. Reference is also made to progress in the role of semiochemicals in parasitoid activity on Ch. partellus and sex pheromones in the control of Con. ignefusalis. Unless resistance levels to stemborers are increased through biotechnological approaches, optimisation of the yield potential in existing cultivars requires that IPM research should focus on the improvement of cultural and biological components and should incorporate farmers' perceptions and an assessment of traditional pest management practices.

A systematic account of the lepidopterous cereal stemborers in Africa is presented. The identification and distribution of the economically important species is discussed. Systematic problems are pointed out.

Stemborers in Africa are attacked by a complex of about 120 species of hymenopteran parasitoids, including about 15 species which are either facultative or obligatory hyperparasitoids. Several dipteran parasitoids also attack stemborers. An overview of hymenopteran stemborer parasitoids is here presented by superfamily and family, giving numbers of genera and species involved, their biologies (where known) and distributions.

The noctuids Busseola fusca and Sesamia calamistis and the pyraloids Chilo partellus, Chilo orichalcociliellus and Eldana saccharina are the most important stemborers of maize in East Africa. A wide range of egg, larval and pupal parasitoids of stemborers have been identified, but information on predators, nematodes and microbial pathogens is less extensive. The most abundant and widespread parasitoids in the East African region are the egg parasitoids Telenomus spp. and Trichogramma spp., the larval parasitoids Cotesia sesamiae and Sturmiopsis parasitica and the pupal parasitoids Pediobius furvus and Dentichasmias busseolae. Predators, such as ants, spiders and earwigs can cause high mortality of eggs and young larvae in some areas. Nematodes and microbial pathogens have been reported to infect all life stages, but their impact is low under natural conditions. The abundance of natural enemies can vary considerably between locations and seasons. In general, indigenous natural enemies are not able to keep stemborer populations below economic injury levels. This paper summarises what is currently known of the natural enemies of cereal stemborers in East Africa.

Patterns of stemborer life history and the foraging patterns exhibited by a taxonomically diverse array of stemborer parasites are described. Foraging strategies provide functional descriptions of natural parasite groupings and include elements of the guild concept plus ecological, behavioural, and morphological adaptations that enable a parasite to locate and exploit a particular host effectively. Elements of the foraging strategy include: host stage attacked, microhabitat of the host, cues employed to locate and identify the host, and method of host attack. Possible constraints presented by the crop plants to the success of different foraging strategies exhibited by groups of parasites are explored.

One tactic of importation of natural enemies for biological control of stemborers and other pests is the use of parasite species that have had no previous association with the pest. This ‘novel association’ approach offers the possibility of using parasites that have proven effective against a stemborer species other than the target stemborer pest. Nevertheless, creation of a novel host-parasite association requires that the novel host be ecologically and physiologically equivalent to the ancestral host. Selecting natural enemies based on ecological and physiological equivalence offers the best possibility of temporal, behavioural, nutritional and immunological compatibility in the host-parasite interaction, and reduces the chances of failure with the imported parasite species.

The stemborers Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), are the most important pests of maize and grain sorghum in South Africa. Parasitoids, pathogens and predators curtailed populations of B. fusca and C. partellus on the crops but their activity was not enough to reduce pest populations to below-economic-damage levels. They also could not prevent the dispersal and subsequent widespread distribution of C. partellus after its introduction into South Africa. Nine parasitoids and hyperparasitoids have been recorded attacking both borer species. These parasitoids are probably more habitat-specific with regard to foraging for hosts than they are host-specific, as they appear to have moved from their indigenous hosts to use C. partellus as a new alternative host. Between 1977 and 1993 three braconids, one eulophid, three ichneumonids, two trichogrammatids and four tachinids were introduced into South Africa from 11 countries for biological control of stemborers. Recoveries of parasitoids were made only short periods after releases and in the vicinity of the release sites. Cold and dry winters, with night temperatures often falling to below freezing, prevail in the Highveld Region which is the major summer-grain-producing area of South Africa. These conditions, and the fact that borers enter diapause in the dry stalks for 7 months in winter, when the crops or other alternative host plants such as grasses do not grow, hamper the establishment of exotic natural enemies in the Highveld Region.

The progress of the South African Sugar Association Experiment Station's 15-year-old biological control programme against Eldana saccharina Walker is reviewed. Two approaches at controlling this borer, a ‘new association’ and a ‘modified’ classical biological approach are summarised. Constraints identified as limiting the successful establishment of 10 egg, 12 larval and 2 pupal ‘new association’ parasitoids include host incompatibility, climatic incompatibility, poor ecological and biological life history knowledge, incorrect parasitoid searching ability and hyperparasitic tendencies. The 3 egg and 7 larval ‘modified’ classical biocontrol parasitoids which could be reared in the laboratory had constraints such as parasitising ability, different host habitat, differing host behaviours in different habitats and initial host identification difficulties to overcome. Difficulties encountered in this biological control programme against an indigenous pest insect show that biological control is not easy. Knowledge of constraints identified during this programme will hopefully be of use to others embarking on similar projects.

Chilo partellus Swinhoe (Lepidoptera: Pyralidae) is an exotic stemborer of cereal crops in Africa which invaded the continent from Asia earlier this century. In addition to Ch. partellus, several indigenous stemborers are found in Africa. In 1991, Cotesia flavipes Cameron (Hymenoptera: Braconidae), a gregarious endoparasitoid of stemborers in Asia, was introduced into Kenya for biological control of Ch. partellus. Laboratory studies revealed that the parasitoid could successfully parasitise not only the target stemborer, but also two native stemborers that occur sympatrically with Ch. partellus in some locations. Interbreeding studies demonstrated the Co. flavipes would mate with a native congener, Cotesia sesamiae (Cameron), but no female offspring resulted from these matings. Investigations on competition between the two Cotesia spp. indicated that when Ch. partellus was the host, Co. flavipes appeared to be a superior parasitoid. Releases of Co. flavipes were made in 1993 in Kenya. Recoveries in 1994,1995 and 1996 demonstrated that the parasitoid was firmly established in two regions of Kenya and in northern Tanzania. Preliminary observations suggest that the parasitoid is causing greater mortality to stemborers in southwestern Kenya than in the coastal area.

The palaeotropical, gregarious, endoparasitic braconids Cotesia sesamiae, Cotesia flavipes and Cotesia chilonis were recently imported into Benin as candidates for biological control of stem and cob borers of maize. Host acceptability and host suitability of six gramineous borers occurring in western Africa, namely the noctuids Sesamia calamistis, Sesamia poephaga, Busseola fusca and the pyralids Coniesta ignefusalis, Eldana saccharina andMussidia nigrivenella, to these candidate parasitoids was evaluated in order to gain insight into the physiological suitability of the natural and factitious hosts. All hosts were accepted by all Cotesia spp., except M. nigrivenella which was not attacked by Co. chilonis. Parasitoid progeny development was successful in S. calamistis, S. poephaga and Con. ignefusalis. Sesamia calamistis was the most suitable host for Cotesia spp. development, in terms of duration of developmental time, brood size and mortality of parasitoid progeny.

Difficulties of identification of natural enemies of cereal stemborers for ‘redistribution’ in Africa are discussed. Tritrophic level studies on wild and cultivated habitats of borers and beneficial species are needed to judge the impact of a natural enemy species in the cropping system. Areas with low pest pressure which are climatically favorable for pest development may be selected for study. Based on the results of various countrywide surveys to map the relative importance of Sesamia calamistis Hampson, Eldana saccharina (Walker) and Busseola frisca (Fuller) in western Africa, recommendations are given for sites for tritrophic level studies. It is hypothesised that because maize is not always present in the field and because of its high susceptibility, natural biological control has to come from wild habitats. This emphasises the importance of the knowledge on the wild host-plant range. Survey results complemented with oviposition and life-table studies in the laboratory showed that, rather than being reservoirs for pests, most wild grass species act as trap plants causing mortalities of 100%. A comparison of light trap catches with pupae found on wild hosts and the scarcity of known wild hosts in areas with high pest pressure suggest gaps in our knowledge of the range of host plant species. Based on comparison of known natural enemy complexes in East and West Africa, the scelionid egg parasitoid Telenomus isis and an East African strain of the braconid larval parasitoid Cotesia sesamiae (Cameron) are proposed for redistribution against B. fusca and S. calamistis, respectively. Telenomus isis has never been reported from East Africa whereas G sesamiae is common in East and southern Africa and scarce in western Africa, suggesting that G sesamiae is probably not adapted to S. calamistis and B. fusca in this region.

Cotesia flavipes (Hymenoptera: Braconidae) is a braconid larval parasitoid that has been used in the biological control of tropical stemborers in gramineous plants. The current research status on the behavioural ecology of this parasitoid is reviewed. The stimuli involved in the location of the host-microhabitat and the behaviour on infested plants and inside stemborer tunnels are discussed. Several aspects of the host foraging behaviour on C. flavipes are discussed in relation to the ecology of the parasitoid, such as the role of learning in foraging and clutch size allocation decisions. Variation in behaviour can be an obstacle in the effective use of natural enemies in biological control. Behavioural variation may exist because individuals differ genetically in their propensity to find or accept different hosts. Individuals may also differ because they have experienced different environments (i.e. learning). The second part of this paper focuses on the intraspecific variability in G flavipes behaviour and discusses to what extent the reported plant and host specificity in C. flavipes has a genetic basis or is due to phenotypic plasticity through learning.

The biosystematics of species in the Cotesia flavipes complex is reviewed with reference to studies conducted on their morphology, morphometrics, enzyme electrophoresis and hybridisation. A survey of 5 morphological characters scored from 17 populations indicated that the scuto-scutellar sulcus and the rugosity on the propodeum could be used to separate the species. The shape of the male genitalia was valid for separating the populations of C. flavipes from those of C. sesamiae and C. chilonis. Canonical variate analysis separated the complex into three distinct clusters with populations from Africa together, populations from Asia and the neotropics forming a second cluster, and material from China and Japan forming the third cluster. Electrophoretic studies showed that esterase, glucosephosphate isomerase, hexokinase, sorbital dehydrogenase and phosphogluconate dehydrogenase, among others, had fixed alelles and could be used to distinguish the species. Cladistic analysis of the allozyme data indicated that allopatric populations currently included in C. flavipes may not be a monophyletic group. Interspecific crosses revealed that males of C. sesamiae could mate with females of C. chilonis and produce viable females.

Laboratory experiments using a glass tube arena were conducted to determine the effects of aggressive behaviour of the stemborer, Chilo partellus Swinhoe (Lepidoptera: Pyralidae), on oviposition success and mortality of the parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae). On contacting unparasitised hosts, female parasitoids rapidly oviposited and then retreated from the experimental arena. Hosts exhibited no aggressive behaviour prior to oviposition. However, soon after being attacked, host larvae became more aggressive, spitting at and biting the parasitoids. When Co. flavipes females were introduced toward the head of the stemborer, the parasitoids stung the host near the head and were frequently bitten and killed by the hosts. Parasitoids that were introduced to the host from the posterior end of the abdomen, stung the abdomen and were often able to escape from the host without being bitten. Regardless of whether parasitoids were introduced near the head or the abdomen, they were more often killed by older hosts than younger hosts. Parasitised hosts were more aggressive than unparasitised hosts one hour after the initial parasitisation, but not after 24 hours. Larval saliva of Chilo partellus was found to reduce survival of adult female parasitoids. The aggressive behaviour of Ch. partellus was not effective as a self-defense against Co. flavipes, but is likely to be an important mortality factor of Co. flavipes in nature.

Progeny production and sex ratios of the parasitoids Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) and its exotic congener Cotesia flavipes Cameron (Hymenoptera: Braconidae) emerging from three species of field-collected stemborers were compared. There were no significant differences in numbers of progeny of the two parasitoids from the African stemborers, Chilo orichalcociliellus (Strand) (Lepidoptera: Pyralidae) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Cotesia flavipes produced more progeny than C. sesamiae on large larvae of its coevolved Asian host, Chilo partellus (Swinhoe). No significant differences in the number of parasitoid progeny were observed for different-sized Ch. orichalcociliellus or S. calamistis larvae. These data suggest that under field conditions, Co. flavipes may be superior to Co. sesamiae as a parasitoid of its co-evolved host, Ch. partellus.

Field trials in Kenya demonstrated that the forage grass, Sorghum vulgare sudanense (Sudan grass) attracted greater oviposition by stemborers than cultivated maize, resulting in significant increase in maize yield. On the other hand, the non-host forage plant, Melinis minutiflora (molasses grass), when inter-cropped with maize, repelled gravid stemborer females from ovipositing on maize, resulting in significant reduction in stemborer infestation. Using these trap- and repellent gramineous plants, a novel pest management approach based on a ‘push-pull’ or stimulo-deterrent diversionary strategy is being developed where stemborers are repelled from the food crop and are simultaneously attracted to a discard or trap crop. The plant composition and permanence of habitat surrounding maize fields also influence the abundance of natural enemies that invade agroecosy stems once a pest population is present. It may be advantageous to promote the growth of native Gramineae and other wild plants which minimise, or even suppress, population growth of pests during non-cropping seasons, but still provide a suitable habitat for natural enemies.

Two field experiments were conducted over two seasons to assess the effect of resistance levels of sorghum varieties on follow-up generations of Chilo partellus. Sorghum varieties, released by the Southern African Development Community/International Crops Research Institute for the Semi-Arid Tropics (SADC/ICRISAT) through the Sorghum and Millet Improvement Program (SMIP) in the southern African region, were evaluated for their ability to provide for larvae to complete development in stalks and emerge as moths. Plants were naturally infested by C. partellus. The number of moth exit holes per stem was used to calculate survival of larvae to the adult stage. A moth production index was calculated to estimate the role of each sorghum variety in area-wide suppression of stemborer abundance. Between 97,500 and 213,125 moths per hectare emerged from the different sorghum varieties in trial 1 while between 0 and 77,500 emerged per hectare in trail 2. Resistant sorghum varieties may help suppress pest population build-up and be of considerable value in development of IPM systems for resource-poor farmers.

Transgenic plants expressing Bacillus thuringiensis δ-endotoxins are now being used commercially in several crop species. These toxins have demonstrated good control of temperate (Ostrinia nubilalis) and tropical (Diatraea grandiosella and D. saccharalis) stemborers in maize. Resistance to B. thuringiensis toxins has been reported in over 11 species in both field and laboratory studies, demonstrating the need for resistance management strategies to prolong the efficacy of this valuable pest management tool within an integrated control programme. Resistance involves reduced binding of toxins to midgut epithelial cells and is generally considered to be a recessive trait. Resistance management will require the use of spatial and temporal refugia which may require unique schemes for each pest complex. Information is presented on the mode of action of cry toxins, resistance mechanisms, interaction of transgenic plants and biocontrol agents, and management/deployment strategies for transgenic maize in tropical ecologies.

Recent studies on the identification and evaluation of the millet stemborer Contesta ignefusalis female sex pheromone have shown that pheromone technology is promising as a management component. A review of research shows that an effective pheromone trap has been developed and successfully tested in eight countries in West Africa, through the West and Central African Millet Research Network (WCAMRN/ROCAFREMI). A regional wide-scale stemborer monitoring network has been developed and is being implemented. Studies on mass trapping and mating disruption indicate that the two techniques have much potential in C. ignefusalis management. Prospects for the implementation of pheromone technology to manage C. ignefusalis in the context of an IPM scheme are discussed.