Kanayo F. Nwanze

Identification and utilization of resistance to sorghum midge, Contarinia sorghicola (Coquillet), in India

Sorghum midge, Contarinia sorghicola (Coquillet), is a most important and widespread pest of grain sorghum. Over 15 000 germplasm accessions and several thousand breeding lines have been screened for resistance to sorghum midge under field infestation and no-choice headcage conditions in India. Twenty-seven germplasm accessions showing resistance across seasons and locations have been identified, of which TAM 2566, AF 28, DJ 6514, IS 3461, IS 8918, IS 10712, IS 21871 and IS 27103 are diverse sources of resistance to sorghum midge. Substantial progress has been made in developing improved midge-resistant breeding lines with reasonable yield and grain quality. Forty-four lines improved for plant type and grain yield have been developed. ICSV 197, ICSV 745, ICSV 843, ICSV 88013 and ICSV 88032 have high levels of midge resistance and their yield potential is comparable to that of commercial cultivars. PM 7068, ICSV 690, ICSV 563, and ICSV 388 have been identified as non-restorers. ICSV 563 and PM 7068 have been converted into male-sterile hybrid parents. Sorghum lines with midge resistance are genetically and morphologically diverse, and can be adapted per se or used in sorghum improvement in different sorghum-growing regions.

Effect of cytoplasmic male-sterility in sorghum on host plant interaction with sorghum midge, Contarinia sorghicola

SummarySorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is one of the most important pests of grain sorghum worldwide. We studied the reaction of midge-resistant and midge-susceptible genic-cytoplasmic male-sterile (A-lines) and their maintainers (B-lines), and the effect of resistant and susceptible restorers on sorghum midge. Midge damage and adult emergence were significantly lower on the B-lines of midge-resistant genotypes (PM 7061 and PM 7068) than their corresponding A-lines, while the reverse was true for the midge-susceptible genotypes (296A and ICSA 42). Differences in midge damage and the number of midges emerged were not significant between the midge-resistant and midge-susceptible A-lines when infested without pollination (except midge emergence on PM 7061A). Pollination with a midge-resistant restorer (DJ6541) reduced midge emergence significantly in one of two seasons. Source of pollen did not influence midge emergence on the highly-resistant A-line, PM 7061A. The implications of these observations in the development of midge-resistant hybrids were discussed.

Insect pests of pearl millet in Sahelian West Africa—II. Raghuva albipunctella De Joannis (Noctuidae, Lepidoptera): Distribution, population dynamics and assessment of crop damage

Abstract Pest surveys in farmers’ fields were conducted for Raghuva albipunctella infestations on pearl millet in Burkina Faso, Niger and northern Nigeria in 1980–1983. Field studies on the seasonal fluctuations of moths and diapausing pupae, assessment of crop damage and grain yield loss were conducted in Niger. The results indicated that R. albipunctella occurred between latitudes 11° N and 15 ° N, within the Southern Sahel and Sudan bioclimatic zones. R. albipunctella is a univoltine species, and off‐season carryover is through diapausing pupae in the soil. The majority of diapausing pupae (51%) were found at 10–20 cm of soil depth. The onset and continuity of rains, favourable soil moisture and temperature conditions were key factors in diapause termination, duration of post‐diapause development and adult emergence. Crop damage and grain yield loss were a function of sowing date, time of panicle exsertion and the occurrence of critical numbers of adult moths. Percentage crop lost varied from 1% to 41%...

Insect pests of pearl millet in Sahelian West Africa I. Acigona ignefusalis (Pyralidae, Lepidoptera): Distribution, population dynamics and assessment of crop damage†

Pests were surveyed in farmers’ fields in Burkina Faso, Niger and northern Nigeria from 1980 to 1983, and field trials at research stations in Burkina Faso (1980 and 1981) and at the ICRISAT Sahelian Center in Niger (1984 and 1985). Acigona ignefusalis is widely distributed in West Africa but its predominance as the major stem borer of millet varies with location. There are two generations of the pest annually, with peaks in moth population in July and September. Diapausing larval population declines during the dry season from November to May. A progressive decline in borer infestation was recorded between 1983 and 1985 in Niger. Damage to early‐sown millet was usually low while late sowing resulted in severe stem tunnelling and unproductive tillers. However, under low levels of borer infestation an unprotected crop gave higher grain yield than one which was protected with insecticide.

Some aspects of pest management and host plant resistance in pearl millet in the Sahel

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.RésuméDe nombreuses espèces d’insectes s’attaquent aux cultures de mil. La mineuse de l’épi, Raghuva albipunctella Joannis, et le foreur des tiges Acigona ignefusalis Hmps, sont considérés comme les deux plus importants, nous faisons état des principales contraintes rencontrées lors de l’établissement d’un programme de lutte intégrée contre ces insectes. Nous comparons le potentiel et l’importance de la résistance de la plante hôte aux autres composantes d’un tel programme.L’utilisation d’insecticides n’est pas réalisable actuellement compte tenu de la très faible rentabilité de cette pratique, des problèmes d’approvisionnement en eau, du niveau de formation des utilisateurs et des carences du système de livraison. Les pratiques culturales de lutte telle la synchronisation de semis hâtifs, l’enlèvement des résidus de récoltes et le labour de fin de campagne permettraient de réduire les populations diapausantes. Cependant, les problèmes rencontrés sont les suivants: formation des paysans, problèmes rencontrés sont les suivants: formation des paysans, problèmes rencontrés sont les suivants: formation des paysans, problèmes rencontrés lors de l’adoption de techniques nouvelles et introduction après la récolte de nouvelles opérations requérant beaucoup de travail. Les ennemis naturels sont de plus en plus efficaces contre Raghuva albipunctella, mais non dans le cas de Acigona ignefusalis. Plusieurs caractères de résistance ont été identifiés: le tallage de certaines variétés augmenterait la tolérance aux foreurs; certains cycles de maturation permettraient d’échapper (pseudorésistance) aux attaques de Raghuva; la pilosité des plantes pourrait servir en fonction des sites préférés pour la ponte; les chandelles compactes entraveraient la pénétration des larves dnas l’épi. La plupart de ces caractères sont présents dans les variétés locales non améliorées. Il reste maintenant à les incorporer dans un matériel génétique agronomiquement supérieur que les paysans accepteront de cultiver. Ce travail ne peut être réalisé que dans le cadre d’un effort de recherche pluridisciplinaire; ce qui est fondamental en lutte intégrée. Dans la plupart des pays d’Afrique, ceux du Sahel plus particulièrement, cette possibilité devient peu à peu réalité.

Integrated Management of Stemborers of Sorghum and Pearl Millet

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, Coniesta 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 cultivars 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.RésuméPlusiers espèces de foreurs de tiges attaquent le sorgho et le petit mil en Afrique et en Asie. Les espèces les plus commones dans le cas du sorgho sont Chilo partellus (Swinhoe) et Busseola fusca (Fuller) et dans le cas du petit mil, Coniesta ignefusalis (Hampson). Le présent document discute des options de contrôle, et de la mesure dans laquelle les perceptions que les agriculteurs ont des foreurs de tiges et des pertes de cultures associées ont été prises en compte. Des exemples de recherche visant à élaborer des stratégies de lutte intégrée sont présentés dans le contexte de leur impact sur la communauté agricole ou en son absence. Les efforts de recherche ont par le passé été axés sur la mise au point de variétés résistants et c’est seulement récemment qu’ils ont été orientés vers une combinaison d’approches culturelles et biologiques. Les procédures conventionnelles de sélection n’ont pas suscité des niveaux adéquats de résistance aux foreurs de tiges, et les ennemis naturels ne sont pas plus en mesure de réguler les populations de foreurs de tiges. Les perspectives du contrôle biologique appliqué et des configurations inter-cultures améliorées font l’objet de discussion. Référence est également faite au progrès réalisé dans le rôle des produits semio-chimiques dans les activités parasitoïdes sur le Ch. partellus et les phéromones du sexe dans la lutte contre Con. ignefusalis. A moins que les niveaux de résistance aux foreurs de tiges ne soient accrus par le biais d’approches biotechnologiques, l’optimisation du potentiel de rendement dans les variétés existants nécessite que la recherche en matière de lutte intégrée soit axée sur l’amélioration des composantes culturelles et biologiques et devraient inclure les perceptions des agriculteurs et une évaluation des pratiques traditionnelles de luttes contre les déprédateurs.

Tritrophic interactions in sorghum, midge (Stenodiplosis sorghicola) and its parasitoid (Aprostocetus spp.)

Abstract Studies on tritrophic interactions involving sorghum genotypes, midge ( Stenodiplosis sorghicola ) and the predominant parasitoids ( Aprostocetus spp.) at ICRISAT Asia Center were conducted using three midge resistant (ICSV 745, ICSV 89058 and IS 10712) and three susceptible (Swarna, CSH 9 and ICSV 112) genotypes during the post-rainy (1992/93) and rainy (1993) seasons. A. coimhatorensis , the predominant parasitoid during post-rainy season, preferred mid-late midge larvae for parasitization, while A. gala, which was predominant during the rainy season, preferred early-mid larval stages. Variations in the preference of A. coimbatorensis and A. gala for the developmental stage of their host larvae indicate good prospects for the biological control of sorghum midge populations. There were significant differences in parasitization level of midge by Aprostocetus spp. between resistant and susceptible sorghum genotypes, and season. Higher parasitization was observed on susceptible genotypes than on resistant ones during both post-rainy and rainy seasons. However, the level of parasitization was greater in post-rainy than in rainy seasons. There was also evidence of higher midge infestation in rainy than in post-rainy seasons. Susceptible genotypes attracted more parasitoids because of high levels of midge infestations. Low parasitoid density in midge resistant sorghum under glasshouse and field conditions was associated with low midge infestations in these genotypes. However, parasitoids were always associated with their host in spite of low midge densities in resistant genotypes. The present study revealed that the interaction between host plant resistance and parasitoids of sorghum midge would thus be synergistic and complementary and could result in successful integration of these two important pest management tactics.

COMPONENTS FOR THE MANAGEMENT OF TWO INSECT PESTS OF PEARL MILLET IN SAHELIAN WEST AFRICA

Pearl millet, Pennisetum glaucum (L.) R. Br. is attacked by over 100 species of insect pests, but only a few of these are of economic importance. The two major ones, the millet stem borer, Contesta ignefusalis Hampson and the earhead caterpillar Heliocheilus albipunctella de Joannis have been the subject of research in the Sahel during the last decade. The various methods that have been suggested for the control of these species are briefly discussed. Generally, the control strategy adopted by farmers involves the use of cultural operations that will reduce insect damage. There are no control measures that have been developed for farmers. The more scientific methods that have been suggested are the results from research trials and experiments. These have several limitations. Future perspectives and considerations for developing sound and practical farmer-oriented practices are discussed.RésuméLe mil, Pennisetum glaucum (L.) R. Br. est susceptible d’être attaqué par plus de 100 espèces d’insectes ravageurs, mais ce n’est quelques espèces qui sont d’une importance économique. Les deux espèces principales, le foreur des tiges du mil, Coniesta ignefusalis Hampson et la chenille des chandelles, Heliocheilus albipunctella de Joannis, ont fait l’objet des travaux de recherche dans le Sahel au cours de la dernière décennie. Les diverses méthodes proposées pour la lutte contre ces insectes sont exposées brièvement dans le présente article. D’une manière générale, la stratégie de lutte adoptée par les paysans consiste à utiliser des opérations culturales permettant de réduire les dégâts causés par les insectes. II n’existe pas de mesures de lutte mises au point pour les paysans en particulier. Les résultats des travaux de recherche et des expériences ont permis de proposer les méthodes plus scientifiques. Mais, celles-ci comportent plusieurs limitations. L’article présente finalement une analyse des perspectives de l’avenir ainsi que des facteurs à prendre en compte pour la mise au point de pratiques valables et efficaces et destinées aux paysans.

Distribution and seasonal incidence of some major insect pests of sorghum in Burkina Faso.

This paper reports the results of extensive pest surveys conducted on farmers’ fields and pest population studies at two national research stations between 1979 and 1981 in Burkina Faso. Major findings indicate that, under normal planting conditions, infestation of the sorghum shootfly, Atherigona soccata is very low in farmers’ fields. This pest appears to be restricted to research stations. Stem borer infestation is caused by a complex of species, and species predominance varies with rainfall. South of latitude 12°N, Busseola fusca is the predominant species but further north it is replaced by Acigona ignefusalis, which is a primary pest of pearl millet. Panicle damage caused by the sorghum midge, Contarinia sorghicola, varies with season; is usually very low in the dry northern Sahelian zone but severe south of latitude 13°N. Maximum midge populations occurred between mid-September and early October.RésuméCet article présente les résultats des enquêtes extensives sur les insectes nuisibles réalisées en champs paysans et dans le cadre des études de population des ravageurs à deux stations de recherche nationales entre 1979 et 1981 au Burkina Faso. La plupart des résultats indiquent que dans des conditions de culture normales, l’infestation de la mouche des pousses du sorgho, Atherigona soccata est très faible en champs paysans. Cet insecte nuisible semble être limité aux stations de recherche. L’infestation par le borer des tige du sorgho est occasionnée par un complexe d’espèces dont la prédominance varie avec la pluviométrie. Au sud de la latitude 12°N, Busseola fusca est l’espèce la plus importante tandis qu’au plus nord elle est remplacée par Acigona ignefusalis, qui est le principal ravageur du mil. Les dégâts causés aux panicules par la cécidomyie du sorgho, Contarinia sorghicola, varient avec la saison. En général, ils sont très faibles dans la région sèche du Sahel du nord mais plus importants au sud de la latitude 13°N. La population de cécidomyies a atteint son niveau maximum entre la mi-septembre et début octobre.

Evidence of shoot fly Atherigona soccata Rondani (Dipt., Muscidae) oviposition response to sorghum seedling volatiles

Abstract: The effects of shoot fly resistant (IS 18551) and susceptible (CSH 5) sorghum seedling volatiles on oviposition of shoot fly were investigated by exposing mated females to various treatments under greenhouse conditions. It is hypothesized that shoot fly susceptible genotype and younger [5–10 days after emergence, (DAE)] seedlings emit different quantities and/or blends of volatiles than resistant or older (14–21 DAE) ones. Shoot fly response was greater to host plant odour alone than to host plant plus fishmeal. Transparent trap with 10 day‐old susceptible seedlings was found to be more effective and efficient for adult attraction than the other two types of traps [live fly trap and black trap]. The present study indicated that shoot fly females are attracted both to the volatiles emitted by the susceptible seedlings, and that phototactic (optical) stimuli that may facilitate orientation to its host for oviposition, but volatile blends associated with adult attraction will be reported in due course to confirm these results.