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TROPICAL ROOT CROPS: RESEARCH STRATEGIES FOR THE 1980s

PROCEEDINGS OF THE FIRST TRIENNIAL ROOT CROPS SYMPOSIUM OF THE INTERNATIONAL SOCIETY FOR TROPICAL ROOT CROPS AFRICA BRANCH, 8-12 SEPTEMBER 1980, IBADAN,

EDITORS: E.R. TERRY, K.A. ODURO, AND F. CAVENESS

Although the editorial chores for these proceedings were the sole responsibility of the editors, the International Society for Tropical Root Crops - Africa Branch has a full Editorial Board comprising E.R. Terry, OB. Arene, E.V. Doku, K.A. Oduro, W.N. Ezeilo, J. Mabanza, and F. Nweke. This Board serves the Society in various editorial capacities at all times. The International Development Research Centre is a public corporation created by the Parliament of Canada in 1970 to support research designed to adapt science and technology to the needs of developing countries. The Centre's activity is concentrated in five sectors: agriculture, food and nutrition sciences; health sciences; information sciences; social sciences; and communications. IDRC is financed solely by the Parliament of Canada; its policies, however, are set by an international Board of Governors. The Centre's headquarters are in Ottawa, Canada. Regional offices are located in Africa, Asia, Latin America, and the Middle East.

I The International Society for Tropical Root Crops - Africa Branch was created in 1978 to stimulate research. oroduction. and utili7tinn (If rn(It nd tiihrernn in Africa and the adjacent islands. The activities include encouragement f training and extension, organization of workshops and symposia, exchange of genetic materials, and facilitation of contacts between personnel working with i root and tuber crops. The Society's headquarters is at the International Institute I of Tropical Agriculture in Ibadan, Nigeria, but its executive council comprises I eminent root and tuber researchers from national programs throughout the continent.

© 198 1 International Development Research Centre Postal Address: Box 8500, Ottawa, Canada K1G 3H9 Head Office: 60 Queen Street, Ottawa

Terry, E.R. Oduro, K.A. Caveness, F. International Society for Tropical Root Crops. Africa Branch, Ibadan NG IDRC-l63e Tropical root crops: research strategies for the 1980s. Ottawa, Ont., IDRC, 1981. 279 p. : ill.

/IDRC publication!, /root crops!, !agricultural research! !plant breeding!, !plant - diseases!, !cassava!, /sweet potatoes! , !pests of plants! , !plant production! !weed , control! !intercropping! , !harvesting! , !crop yield! , !conference report! , !list of participants! , !agricultural statistics!.

UDC: 633.4 (213) ISBN: 088936285 8

Microfiche edition available Cooperating institutions

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LE CANADA CONTENTS

Foreword E.R. Terry 7 Participants Welcoming Addresses Bede N. Okigho, President, International Society for Tropical Root Crops - Africa Branch 15 Alhaji Ibrahim Gusau, Minister of Agriculture, Nigeria 17 S. Olajuwon Olayide, Vice-Chancellor, University of Ibadan, Nigeria 19 E. Hartmans, Director-General, International Institute of Tropical Agricul- ture, Nigeria 22 Cassava Cassava Improvement Strategies for Resistance to Major Economic Diseases and Pests in Africa S.K. Hahn, E.R. Terry, K. Leuschner, and T.P Singh 25 Cassava Improvement in the Programme National Manioc in Zaire: Objectives and Achievements up to 1978 H.C. Ezumah 29 Assessment of Cassava Cultivars for Extension Work C. Oyolu 35 Breeding Cassava Resistant to Pests and Diseases in Zaire T.P. Singh 37 Selection of Cassava for Disease and Pest Resistance in the Congo Joseph Mabanza 40 Some Characteristics of Yellow-Pigmented Cassava K.A. Oduro 42 - Cassava: Ecology, Diseases, and Productivity: Strategies for Future Research E.R. Terry 45 Field Screening of Cassava Clones for Resistance to Cercospora hennin gsii J.B.K. Kasirivu, O.F. Esuruoso, and E.R. Terry 49 Properties of a Severe Strain of Cassava Latent Virus Isolated from Field- Grown Tobacco in Nigeria E.C.K. Igwegbe 58 Cassava Bacterial Blight Disease in G.W. Otim-Nape and T Sengooba 61 Dissemination of Xanthomonas manihotis to Cassava in the People's Republic of Congo J.F. Daniel, B. Boher, and N. Nkouka 66 Cassava Root Rot due to Armillariella tabescens in the People's Republic of Congo Casimir Makambila 69 Screening for Resistance Against the Green Spider Mite K. Leuschner 75 Biological Control of the Cassava Hans R. Herren 79 Entomophagous Associated with the Cassava Mealybug in the People's Republic of Congo G. Fabres 81 Dynamics of Cassava Mealybug Populations in the People's Republic of Congo G. Fabres 84 Consumption Patterns and Their Implications for Research and Production in Tropical Africa Felix I. Nweke 88

3 Problems of Cassava Production in R.F. Nembozanga Sauti 95 Evaluation of Some Major Soils from Southern Nigeria for Cassava Produc- tion J.E.OkekeandB.T.Kang 99 Effects of Soil Moisture and Bulk Density on Growth and Development of Two Cassava Cultivars R. LaI 104 Performance of Cassava in Relation to Time of Planting and Harvesting F.0.C. Ezedinma, D.G. Ibe, and A.I. Onwuchuruba 111 The Effects of Previous Cropping on Yields of Yam, Cassava, and Maize S.0. Odurukwe and U.I. Oji 116 Intercropping of Plantains, Cocoyams, and Cassava S.K. Karikari 120 Weed Control in MaizeCassava Intercrop I. Okezie Akobundu 124 Effect of Maize Plant Population and Nitrogen Application on MaizeCassava Intercrop B.T. Kang and G.F. Wilson 129 Cassava Leaf Harvesting in Zaire N.B. Lutaladio and H.C. Ezumah 134 Effects of Leaf Harvests and Detopping on the Yield of Leaves and Roots of Cassava and Sweet Potato M.T. Dahniya 137 Metabolism, Synthetic Site, and Translocation of Cyanogenic Glycosides in Cassava M.K.B. Bediako, B.A. Tapper, and G.G. Pritchard 143 Loss of Hydrocyanic Acid and Its Derivatives During Sun Drying of Cassava Emmanuel N. Maduagwu and Aderemi F. Adewale 149 The Role of Palm Oil in Cassava-Based Rations Ruby T. Fomunyam, A.A. Adegbola, and 0.L. Oke 152 Comparison of Pressed and Unpressed Cassava Pulp for Gari Making M.A.N. Ejiofor and N. Okafor 154 Gari Yield from Cassava: Is it a Function of Root Yield? D.G. Ibe and F.0.C. Ezedinma 159

Yams Parameters for Selecting Parents for Yam Hybridization Obinani 0. Okoli 163 Anthracnose of Water Yam in Nigeria Okechukwu Alphonso Nwankiti and E.U. Okpala 166 Strategies for Progress in Yam Research in Africa I.C. Onwueme 173 Study of the Variability Created by the Characteristics of the Organ of Vegetative Multiplication in Dioscorea alata N. Ahoussou and B. Toure 177 Growth Pattern and Growth Analysis of the White Yam Raised from Seed C.E. Okezie, S.N.C. Okonkwo, and F.!. Nweke 180 Artificial Pollination, Pollen Viability, and Storage in White Yam M.0 Akoroda, J.E. Wilson, and H.R. Chheda 189 Improving the In-Situ Stem Support System for Yams G.F. Wilson and K Akapa 195 Yield and Shelf-Life of White Yam as Influenced by Fertilizer K.D Kpeglo, G.0. Obigbesan, and i.E. Wilson 198 Weed Interference in White Yam R.P.A Unamma, 1.0. Akobundu, and A.A.A.Fayemi 203 The Economics of Yam Cultivation in S.N. Lyonga 208 Effect of Traditional Food Processing Methods on the Nutritional Value of Yams in Cameroon Alice Bell and Jean-Claude Favier 214 Cocoyams Strategies for Progress in Cocoyam Research E.V. Doku 227 Root and Storage-Rot Disease of Cocoyam in Nigeria G.C. Okeke 231

4 Fungal Rotting of Cocoyams in Storage in Nigeria J.N.C. Maduewesi and Rose C.!. Onyike 235 A Disease of Cocoyam in Nigeria Caused by Corticium rolfsii O.B. Arene and E.U. Okpala 239 Cocoyam Farming Systems in Nigeria H.C. Knipscheer and i.E. Wilson 247 Yield and Nitrogen Uptake by Cocoyam as Affected by Nitrogen Application and Spacing M.C. Igbokwe and J.C. Ogbannaya 255

Abstracts Cassava Research Program in Mallik A-As-Saqui 259 Effects of Cassava Mosaic on Yield of Cassava Godfrey Chapola 259 Effects of Green Manure on Cassava Yield James S. Squire 260 Alleviating the Labour Problem in Yam Production: Cultivation without Stakes or Manual Weeding !.C. Onwueme 260

Discussion Summary Strategies for the 1980s 263

References 265

5 ENTOMOPHAGOUS INSECTS ASSOCIATED WITH THE CASSAVA MEALYBUG IN THE PEOPLE'S REPUBLIC OF CONGO

G. FABRES

OFFICE DE LA RECHERCHE SCIENTIFIQUE ET TECHNIQUE OUTRE-MER, BRAZZA VILLE, PEOPLE'S REPUBLIC OF CONGO

The study reported here is a contribution to the knowledge of the entomophagous insects associated with the cassava mealybug in Congo. It must be considered as a step toward the development of a reliable pest management strategy. The occurrence of several predators, parasites, and hyperparasites is reported and their relationship is studied in detail. A new species of the genus Anagyrus is recorded. Several Coccinellids (Exochomus fiaviventris, Exochoinus concavus, Hperaspis senegalensis), Cecidomyiids (Coccodiplosis citri, Dicrodiplosis sp.), Lycaenid ( 1ers aiea), and Anthocorid (Cardiasthetus exiguus) are involved in the natural regulation of the pest population. Hyperparasites (Xyphigaster pseudococci, Homalotylus fiaminius, Prochiloneurus pulchellus) have been found attacking Anagyrus, Exochomus, and Coccodipiosis species. An additional Encyrtid (Cheiloneurus evanonotus) develops upon the hyperparasite Homalotyius. Data are given on the dynamics of the entomophagous insect populations, the time of their intervention, and the rates of parasitism and predatism.

La présente étude a apporté des lumières aux connaissances sur les insectes entomophages susceptibles d'être employés au Congo dans la lutte contre la cochenille du manioc. Elle constitue un progrès pour le développement d'une stratégie sûre de lutte contre les ennemis du manioc. Elle contient les recherches détaillées effectuées sur l'apparition de plusieurs prédateurs, parasites et hyperparasites et l'action qu'ils exercent les uns sur les autres. Une nouvelle espèce du gène Anagvrus est mentionnée. Plusieurs coccinellidés (Exochoniu.c fia viventris, Exochoinus conca vus, Hyperaspis senegalensis), cecidomyidés (Coccodiplosis citri, Dicrodiplosis sp.), lycaenidés (Spaigis leinolea), et anthocoridés (Cardiasthetus exiguus) jouent un rôle dans le contrôle naturel de la population des ennemis du manioc. Les hyperparasites (Xyphigaster pseudococci, Honiaiotvlus jiaminius. Prochiloneurus pulchellus) attaquent les espèces Anagyrus, Exochoinus et Coccodipiosis. Et une autre encyrtidé (Cheiloneurus cyanonotus) parasite et hyperparasite Hornalotylus. Le document fournit des données sur la dynamique des populations d'insectes entomophages, la période de leur action et le taux de parasitisme et de destruction. man ihoti appeared in cassava The problem presented by P. manihoti, there- plantations in the Congo in 1973 (Sylvestre 1973). fore, is the presence of a pest in a new biogeo- The rapid increase in this crop-destroyer's popula- graphic area away from its natural biological con- tions and the intensity of its ravages during the dry trols. In this case, experts are considering applying seasons in 1974 and 1975 led to a mission by the biological control techniques by introducing National Museum of Natural History (Matile-Fer- entomophagous insects (Greathead 1978). To this rero 1976) and to a detailed morphologic study of end, the laboratories of the Commonwealth Insti- this Pseudococcidae (Matile-Ferrero 1977). tute for Biological Control in Trinidad have under- P. manihoti is a new species, morphologically taken an inventory of the entomophagous insects of related to the Caribbean P. surinamensis (Williams Phenacoc cus in South America and the breeding of in Bennett and Greathead 1978). Its neotropical a number of species that appear interesting in this affinities were confirmed by Matile-Ferrero (1977) regard. A campaign for the introduction and release who found P. manihoti in samples from Brazil and of parasites originating in the New World was by Bennett and Greathead (1978) who attribute the already organized in Zaire in 1978 (Girling 1978). recent pullulations of pseudococcins on cassava in For the Congo, where an identical operation is at Amazonia to this species (Albuquerque 1977). the project stage (Girling 1979), my colleagues and The presence of P. manihoti in Central Africa I judged it indispensable to begin with a study of and its rapid spread and sudden increase in popula- the local entomofauna associated with the lion are due to a recent accidental introduction from mealybug and an analysis of the biocenotic South America. equilibrium established following the pest's intro-

81 duction. Following a year of collections, field of gradation. E. concavus is found mostly at the observations, and laboratory studies, we can now beginning of the retrogradation; its numbers are provide the first quantitative report giving a fairly smaller and its appearance very short-lived. H. complete, faithful picture of P. manihoti's senegalensis appears at the end of the gradation biocenosis. and, like the preceding species, remains in the plantations for only 4 or 5 weeks. During one dry season, the prevalences for the three species ENTOMOCENOSIS COMPONENTS gathered by various methods were E. fiaviventris, 38.1%, E. concavus, 23.5%, andH. senegalensis, PRIMARY ENTOMOPHAGOUS INSECTS 38.4%. In the absence The primary entomophagous insects belong to of data on the biology and five main orders: the Hymenoptera Chalcididae behaviour of these species, it is difficult to estimate (Encyrtidae), which are internal parasites of the these predators' control potential. Our first quan- mealybug, and the Coleoptera (Coccinellidae), titative report shows that when the host is in the Diptera (Cecidomyiidae), (Anthocori- pullulation phase, and for a total density of 1000 dae), and (), which are per shoot apex, it is possible to collect on predators of the mealybug. each apical colony an average of 12-15 E. fia viventris or The parasites recorded to date in Zaire and the H. senegalensis adults. Congo belong to the genus Anagyrus, which com- Other species less closely associated with the prises many species that are primary parasites of mealybug are also collected on the colonies. Thus, Pseudococcidae. In Zaire there are two species, one we have inventoried Scymnus rufifrons, S. of which is related to A. bugandaensis (Girling plebejus, Sthethorus endruedyi, Serangium giffar- 1979); in the Congo, only one species appears to be di, Nephus derroni, and Platynaspis sp. interesting from an ecological point of view. It does Three species of Cecidomyiid predators were not correspond to any description made to date, and obtained in hatchers by Matile-Ferrero in 1976: a morphological study is at present under way. Coccodiplosis citri, Dicrodiplosis sp., and Les- Anagyrus n.sp. prefers to parasitize the todiplosis related to the Aonidiella. During the mealybug's third larval stages and the young 1978 and 1979 campaigns, on samples of old larvae females. Its attack is usually limited to a few taken in colonies of P. manihoti, I found only the sections of the colony; thus, there appears to be first two species. The second is probably a predator little host-seeking activity for egg-laying. The of F. virgata, like L. aonidiellae in the Congo highest rates of parasitism are observed at the peak (Harris 1968). The genera Dicrodiplosis and Coc- of gradation of P. manihoti populations (Septem- codiplosis are represented in by many ber October 1979). They then fluctuate between 3 species, all of which are predators of Pseudococ- and 5% of potential hosts. A paper on the interven- cidae. C. citri is known in South Africa on tion of Anagyrus n.sp. during the mealybug's citri (Barnes 1935). period of pullulation is in preparation. The most numerous species on mealybug popu- Of the Coccinellidae predators, Exochomus lations in the Congo is C. citri, which alone flaviventris, E. concavus, and Hyperaspis comprises 90% of the individuals raised in hatch- senegalensis are the three dominant species. ers. Fluctuations in this predator's numbers show Although all three have been described in Ethiopia two maxima at the beginning and end of the and observed in many countries of intertropical gradation of the pest's populations. As with Coc- Africa, little work has been done on their biology or cinellidae, I can only give a rough estimate of the control potential (Annecke 1969; Brown 1972, relationship between the density of the host and that 1974). Species belonging to these two genera are of the predator. An apex harbouring 1000 or 1200 very polyphagous and prey on the Homoptera mealybugs in all stages holds a maximum count of Pseudococcidae, Diaspididae, Lecanidae, 50-60 old C. citri larvae (August and November Aphididae, and Aleyrodidae (Thompson and Sim- 1979). monds 1965). The Lycaenidae is whose cater- The intervention of these three species within P. pillars prey on the eggs and all development stages manihoti's biocenosis is complementary. E. of some Pseudococcidae and Lecanidae. This fiaviventris appears in JuneJuly at the beginning species is already known for attacks on F. virgata of the mealybug's population gradation, and it can and several species of of Central still be found at the onset of the first rains when the Africa (Stempffer 1957). The onisciform caterpil- mealybug becomes scarce. Its maximum popula- lars, covered with waxy debris from Phenacoccus, tion density is observed in September, at the peak hide among their prey. The originality of the

82 biology and morphology of this species' larval and manihoti's biocenosis, it behaves in fact as a nymphal stages has sparked many studies, the latest parasite of Anagyrus n.sp. It intervenes very late in being that of Hinton (1974). The presence of this the gradation mechanism (end November) and, on species is constant, regardless of the size of the very low populations of Anagyrus n.sp., may reach mealybug population, but its numbers remain low rates of parasitism of about 30%. and there are no noticeable fluctuations in relation to the host's population dynamics. CONCLUSIONS With regard to Anthocoridae predators, when the host is in the pullulation phase, isolated individuals The entomocenosis associated with P. manihoti of Cardiasthetus exiguus are regularly found, in populations in the Congo is very diversified, in hatchers and on limed traps. Very little is known of regard to both the organisms it comprises and their this species' biology and predatory behaviour, but behaviour within mealybug colonies. Five orders of it is reputed to be extremely polyphagous. Locally, insects represented by at least 12 different species it should be noted within P. manihoti's biocenosis. participate in the same ecosystem and contribute to the control of the pest's populations. The entomo- SECONDARY AND TERTIARY PARASITES phagous parasites prey on all the Homoptera's stages of development one after the other. The The secondary and tertiary parasites are the Coccinellidae and the Lycaenidae eat the eggs and Hymenoptera Encyrtidae who parasitize the prim- the females before the secretion of the ovisac; the ary entomophagous insects, behaving as hyperpara- Cecidomyiidae eat the eggs and the young larvae; sites. the Anthocoridae feed on later stages of develop- Collected for the first time in Zaire (Risbec 1958) ment and the Ana gyrus parasitize third stages and on populations of , Xyphigaster young females. There is no doubt that their simul- pseudococci was found again in 1974 in Sao Tomé taneous or successive action throughout the pest's as a parasite of Coccodiplosis coffea (Prinsloo population gradation helps to reduce the impact of 1979). I found it parasitizing C. citri larvae within the mealybug on its host plant. A study of the P. manihoti colonies and can, therefore, confirm its control potential of the primary entomophagous status as a parasite of Cecidomyiids while recording parasites, together with an analysis of the depres- its first appearance in the Congo and on a new host. sive role of the hyperparasites, is at present under Its presence in the biocenosis is very discreet. way. Homalotylusfiaminius is a cosmopolitan species In the face of the uncontrolled development of parasitizing Coccinellidae (Tachikawa 1974). It has this exotic mealybug, researchers are thus witnes- been found in Africa on numerous hosts, among sing the spectacular adaptation of a great variety of them H. senegalensis (Tachikawa 1963). I have not entomophagous insects, with a relay action that found any mention of its parasitizing E. concavus continues throughout the pest's evolution cycle. or flaviventris. Yet it has been observed only on However, the phenomenon is largely one of these two hosts in the Congo. It is a gregarious polyphagous or oliphagous organismsin this case parasite, attacking mainly old Exochomus larvae of predatorswhile the parasite fauna, which has a (three or four adults per host). It intervenes fairly generally more specific, even monophagous, diet, popula- late in the development of the predator's is extremely scarce. tions (OctoberNovember 1975), and its rates of This fact underlies the move toward the intro- parasitism are about 7 10%. duction of parasites originating in the New World. H. flaminius is in turn parasitized by This enrichment of the biocenosis with specific Cheiloneurus cyanonotus. Species of this genus are elements cannot but result in the reinforcement of frequently recorded in Africa as primary parasites the control potential of the indigenous of cochineal insects or coccinellas (Annecke 1971). entomophagous insects. Yet their status is that of a hyperparasite (with a few exceptions, Tachikawa 1974) and C. orbitalis is My thanks to the specialists who kindly identified most known to parasitize the genus Homalotylus. of the entomophagi mentioned above. Prochiloneurus puichellus is known in Ethiopia This paper was originally French; with the author's as a hyperparasite of Pseudococcidae through permission, it was translated into English for inclusion in species of the genus Pseudococcus. Within P. these proceedings.

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