S. R. Singh

The Legume Pod-Borer, Maruca Testulalis (Geyer): Past, Present and Future Research

The legume pod-borer, Maruca testulalis, continues to be a major limitation to successful cowpea cultivation in many countries. During the past decade, research on this insect has increased in scope and intensity at international agricultural research centres and a number of universities. The work that has been done on the biology and control of this pest at the International Institute of Tropical Agriculture (IITA) is briefly discussed with emphasis on the development of a management strategy centred around host plant resistance, and some suggestions for future research direction are given.RésuméLe rongeur de cosse de légume, Maruca testulalis, continue d’être une contrainte majeure de la culture de petit pois (cowpea) dans beaucoup de pays. Au cours de la dernière décennie, la recherche sur cet insecte ravageur a augmenté d’intensité dans les centres de recherche agricole internationaux et dans plusieurs universités. Le travail qui a été effectue sur la biologie et le contrôle de cet insecte ravageur à l’Institut International d’Agriculture Tropicale (IITA) est brièvement discuté, l’accent étant placé sur le développement d’une stratégie de contrôle basée sur la résistance de la plante hôte, et quelques suggestions sur l’orientation future de la recherche sont données.

Host plant resistance for cowpea insect pest management

Insect pests are major constraints in cowpea production. Breeding for insect resistance is a major objective of cowpea improvement programme at IITA. Resistance to leafhoppers and aphids has been incorporated in advanced breeding lines thus eliminating the need for other control measures. Similarly, a moderate level of resistance to thrips and cowpea storage weevil has also been incorporated thus reducing the damage due to these two pests. A moderate level of resistance to legume pod-borer and pod sucking bugs has also been identified and is being incorporated in advanced breeding lines. The long term strategy is to develop cowpea cultivars with multiple resistance to insect and diseases with superior agronomic characters and local adaptability.RésuméLes ravageurs constituent le principal facteur limitant dans le cadre de la production du niébé. C’est pourquoi le programme d’amélioration du niébé de l’Tita a placé la sélection pour la résistance aux insectes nuisibles au premier rang de ses priorités. Ainsi, il est parvenu à incorporer la résistance aux jassides et aux aphides à certaines lignées de sélection avancées, écartant de la sorte le recours à d’autres mesures de lutte. De même, on a pu réduire les dégâts imputables aux thrips et aux bruches des magasins en conférant au matériel de sélection un niveau modéré de résistance à ces deux insectes. Une source de résistance modérée aux foreuses des gousses et au complexe de punaises a également été identifiée, et l’on procède à l’heure actuelle à son incorporation dans des lignées de sélection avancées. La stratégie à long terme du programme consiste à mettre au point des cultivars du niébé dotés d’une résistance multiple aux ravageurs et aux maladies, dotés de caractères agronomiques supérieurs, et adaptés aux conditions locales.

SUITABILITY OF SELECTED LEGUMINOUS PLANTS FOR DEVELOPMENT OF MARUCA TESTULALIS LARVAE

Flowers of eight plant species were evaluated under laboratory conditions for their suitability as larval growth media for the cowpea pod borer, Maruca testulalis. The plants tested were Crotalaria retusa, C. juncea, C. saltiana, C. misereniensis, C. amazonas, Cajanus cajan and the principal host of the borer, Vigna unguiculata (cowpea), was included for comparison. Based on the data obtained on larval mortality and growth indices (GI) the plants were divided into 3 categories namely: I: Those causing 0–30% mortality and having GI value ≥ 60% form suitable host plants. This group only included V. unguiculata. — II: Those plant species causing 30 ≤ 50% larval mortality and having GI value 30% ≤ 60% of the principal host plant (Cajanus cajan, Crotalaria amazonas, C. saltiana, C. mucronata). This group of species is marginally suitable as hosts. — III: Plants causing 50–100% larval mortality and having GI value ≤ 30% of principal host plant (C. retusa, C. juncea and C. misereniensis).

Varietal resistance in the integrated pest management of cowpea pests

Control of cowpea insect pests has been almost entirely achieved through the use of chemicals by progressive farmers. However, the peasant farmer has traditionally tended to rely on chance and has often been unable to obtain yields that would be profitable. This paper examines the farmer’s dilemma and the jrossibility of using host plant resistance (HPR) as an adjunct to other control methods in developing a sound integrated pest management of cowpea pests. The status of HPR in cowpea is reviewed with a view to identifying the areas where progress has been made with respect to the measurement and identification of resistance to formulate an effective integrated pest control program. The difficulties in achieving this are discussed in the light of our present data bank and the diversity of cowpea pests.

Pod hairs as a factor in Vigna vexillata resistance to the pod-sucking bug, Clavigralla tomentosicollis

Two varieties of Vigna vexillata Benth proved more highly resistant, both under field (free‐choice) and screen‐house (no‐choice) conditions, to infestation and damage by the pod‐sucking bug Clavigralla tomentosicollis (Stål.) (Hemiptera: Coreidae) than cowpea (Vigna unguiculata Walp.) varieties. Trichomes on the pod of V. vexillata partly accounted for the resistance. However, other factors in the pod or seeds are involved in the resistance. Because the pod wall of V. vexillata is not tougher than that of cowpeas, biochemical characteristics of pods and seeds of V. vexillata will be further investigated.

Varietal resistance of cowpea to cowpea aphid, Aphis craccivora Koch.

As part of an extensive and systematic programme to find genetic sources of resistance to Aphis craccivora, a major pest of cowpea, Vigna unguiculata, a total of 181 accessions from the germpiasm collection at the International Institute of Tropical Agriculture were screened in glasshouse tests using a simple visual damage scale. Twenty-four accessions showed considerably reduced damage. To confirm these results on IS selected accessions, aphid population growth over 10 days was recorded. Zero aphids were found on three accessions (310,408-P2 and 801); another six accessions had populations of less than 30, compared with 200–400 on susceptible varieties. The other accessions showed only partial antibiosis and/or tolerance.RésuméRésistance variétale de la dolique au puceron de la dolique, Aphis craccivora Koch. Dans le cadre d’un vaste et systématique programme visant à trouver des sources génétiques de résistance à Aphis craccivora, parasite majeur de la dolique, Vigna unguiculata, un total de 181 acquisitions provenant de la collection de plasmes germinatifs de l’Institut International d’Agriculture Tropicale ont été criblées sous serre en utilisant une simple échelle visuelle des dommages causés. Vingt-quatre acquisitions ont montré une réduction considérable des dommages. Pour confirmer ces résultats sur 15 acquisitions sélectionnées, la croissance de la population de pucerons a été mesurée après dix jours. Zéro pucerons ont été trouvés sur trois acquisitions, autres six acquisitions ont montrées populations inférieures à 30, comparées aux populations de 200–400 observées sur les variétés sensibles. Les autres acquisitions montrèrent seulement une antibiose partielle ou/et tolérance.

Presence and effects of chemical toxin on feeding of cowpea aphid, Aphis craccivora Koch (Homoptera: Aphididae) on six highly resistant varieties of cowpea Vigna unguiculata (L.) Walp, (Leguminosae)

Cowpea, Vigna unguiculata (L.) Walp is one of the most important grain legumes produced in Nigeria. It is mostly grown as a mixed crop with cereals in a traditional cereal/legume farming system. Cowpea aphid, Aphis craccivora Koch is the main aphid pest of cowpea. In view of the importance and serious damage caused by aphids, a total of 613 varieties of cowpeas were screened for resistance in International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. During the screening it was found that aphids died faster without reproducing and their longevity was very short on six varieties (Tvu 408 - P2, 801, 310, 266 - P1 2845 and 337-3F0 with high antibiotic properties. These varieties along with one susceptible variety (Tvu.76(Prima) were used for conducting two experiments together to find out the presence of a chemical and their role in aphids feeding and survival. Comparative studies of the number of honey dew drops produced on varieties used in the experiment, and the reaction of the aphids in terms of probing time, longevity and number of nymphs produced on prima painted with the juice of the above mentioned highly resistant varieties, suggested that the resistance factor exists in the form of a toxin or a feeding deterrent. UNISWA Research Journal of Agriculture, Science and Technology Vol. 4 (1) 2000: pp 100-105