Efficacité comparée des insecticides de natures différentes dans la gestion des insectes ravageurs du niébé au Centre du Bénin

Objectif: Le niébé est une importante plante alimentaire dont la production et la valorisation sont d’une grande priorité pour l’amélioration de la sécurité alimentaire de la population. L’objectif de cette étude est de comparer en milieu paysan, l'efficacité du champignon entomopathogène Beauveria bassiana (isolat Bb 115), du mélange Neem (Topbio) - virus MaviMNPV et de l’insecticide chimique Decis (deltaméthrine) dans la gestion des insectes ravageurs du niébé.Méthodologie et résultats: L'essai a été conduit dans trois villages de la zone cotonnière du centre du Bénin (commune de Glazoué). C’est en effet, une zone de grande production du niébé. L’essai a été conduit suivant un dispositif de bloc aléatoire complet avec quatre traitements et trois répétitions par village de la zone. Les traitements comprennent 1) témoin (niébé non traité), 2) mélange Topbio - MaviMNPV, 3) B. bassiana et 4) Decis. L’application du champignon B. bassiana a été faite à la dose de 75 g m.a. (matière active)/ha. Le Décis et le TopBio à 1L /ha. Quant à la suspension virale, la dose de 2.109 OB/ha a été utilisée. Les effets des différents pesticides utilisés sur les densités de populations de M. vitrata, Megalurothrips sjostedti, Clavigralla tomentosicollis, que sur leur dégâts sur les organes reproductifs (boutons floraux, fleurs, gousses) ont été évalués. Des organes fructifères ont été prélevés hebdomadairement pour évaluer le nombre de larves mortes ou vivantes et aussi leurs dégâts sur les boutons floraux, fleurs et gousses. Les rendements en grains ont été également évalués. Bien qu’il y ait une grande variation dans les effets occasionnés par les biopesticides testés, ils ont considérablement réduit la densité de population de Maruca vitrata et des autres espèces d'insectes, Megalurothrips sjostedti et Clavigralla tomentosicollis ainsi que le niveau de dommages sur les organes fructifères. Comparativement au témoin, le rendement global en grains a été amélioré dans le niébé traité. Ainsi, à Glazoué, dans la zone centrale, des rendements meilleurs de 933,03±8,7Kg/ha ont été obtenus avec le champignon B. bassiana.Conclusion et applications des résultats: Ces résultats révèlent clairement que les biopesticides utilisés dans notre étude peuvent réduire significativement les densités des ravageurs ciblés. Cette étude suggère la possibilité de l'utilisation de biopesticides comme des alternatives aux insecticides chimiques dans la lutte contre les ravageurs du niébé.Mots clés : Niébé, insectes ravageurs, insecticide chimique, insecticide biologique, lutte intégré

Elaboration of a biotic index of pollution using macroinvertebrates for the monitoring of Lake Nokoué in Benin

A study on the relationships between the physicochemical parameters and of the macroinvertebrates of the Lake Nokoué was carried out for the purpose of developing a biotic index of pollution. A total of 96 stations were prospected twice during the flooding and the dry seasons from September 2004 to February 2006. At each station, seven physicochemical parameters were measured and macroinvertebrates were collected. Canonical analyses of correspondence were used to show the relations between the parameters of the environment and the macroinvertebrates. A self-organizing map (SOM) of Kohonen allows the categorization of the studied stations into four groups according to different degrees of pollution. Rough scores were allotted to each taxon according to its abundance in the various groups of stations determined by the SOM for each campaign. A synthesis of the data obtained from the four field surveys allows the assignment of a score to each taxon according to its abundance in the different groups of stations. A biotic index was developed and used for the evaluation of the level of pollution of the stations studied. It then emerged that the borders of the lake present a «poor quality» of water; however, during the dry season there is slight improvement.© 2015 International Formulae Group. All rights reserved.Keywords: Biotic index, pollution, invertebrates, lagoons, Benin, West Afric

Variation in biological parameters of cypermethrin resistant and susceptible strains of Helicoverpa armigera from Benin Republic, West Africa

The aim of this survey was to assess the costs of cypermethrin resistance in Helicoverpa armigera strains by using variation in their biological parameters such as fecundity, number of larval slough, development time, weight and survival at each stage of insect development in comparison with susceptible strains. AGB01 and AGB03 are the resistant strains compared respectively with BK77 and OKP01 as susceptible strains. Fecundity, fertility and survival from egg to adult emergence of AGB03 strain were significantly (P < 0.001) lower than those observed in OKP01 strain. No difference (P > 0.05) was observed with time of pre-adult development, survival at each stage of insect development, fecundity and number of larval slough in comparison with AGB01 and BK77 strains. Larvae of AGB01 strain took significantly (P < 0.01) longer time to develop and were significantly (P < 0.01) lighter than BK77 at the same age, but the slower development of larvae of AGB01 strain was counteracted by the shorter times of egg and pupae stages. The lower fecundity, fertility and survival from egg to adult emergence should represent the main costs for the AGB03 strain resistant to cypermethrin.Keywords: Cypermethrin resistance, resistance cost, fecundity, fertility, development tim

A study on <i>Maruca vitrata</i> infestation of Yard-long beans <i>(Vigna unguiculata </i>subspecies <i>sesquipedalis</i>)

AbstractGlobally, Maruca vitrata (Geyer) is a serious yield constraint on food legumes including Yard-long bean (Vigna unguiculata subspecies sesquipedalis). However, there is a dearth of information on its damage potential, distribution and population dynamics in Yard-long beans. In the present study, the level of M. vitrata larval infestation on flowers and pods of Yard-long beans in Sri Lanka was determined with respect to three consecutive cropping seasons, Yala, Off and Maha. Results indicated that larval infestation and abundance varied with developmental stage of flowers and pods, cropping season and their combined interactive effects. Flowers of Yard-long beans were more prone to M. vitrata larval attack compared to pods. Abundance and level of infestation of M. vitrata varied with plant parts, having a ranking of flower buds (highest)>open flowers>mature pods>immature pods (lowest). Peak infestation was observed six and eight weeks after planting on flowers and pods, respectively. Among the three cropping seasons, M. vitrata infestation was found to be higher during Maha and Off seasons compared to Yala. The findings of this study contribute to the identified knowledge gap regarding the field biology of an acknowledged important pest, M. vitrata, in a previously understudied crop in Sri Lanka

Potential use of the Bushmint, Hyptis suaveolens, for the Control of Infestation by the Pink Stalk Borer, Sesamia calamistis on Maize in Southern Benin, West Africa

Maize production in Benin, especially in resource-poor farmers' fields, is constrained by stemborers among other factors. One of the major stemborers in southern Benin is Sesamia calamistis Hampson (Lepidoptera: Noctuidae). African farmers cannot afford to use commercial insecticides for controlling stemborers - they are expensive and unsuitable for durable pest management systems due to eco-toxicity. There is therefore a need for cheaper and environmentally friendly methods and botanicals offer an attractive alternative. The bushmint, Hyptis suaveolens (L.) Poit. (Lamiales: Lamiaceae), was compared with the commercial insecticide Furadan (carbofuran) for the control of S. calamistis on maize Zea mays L. (Poales: Poaceae). Trials were conducted in the screenhouse and in the field during the minor cropping season in 2004 at the International Institute of Tropical Agriculture (IITA)-Benin station. The variables measured included numbers of egg masses per plant, eggs per egg mass (in the screenhouse study), population density of S. calamistis, percentage of infested plants and/or ears, and deadhearts in the field. Irrespective of the variable considered, the aqueous extract of H. suaveolens compared favorably with Furadan while maize surrounded by live H. suaveolens plants had lower S. calamistis densities

Annual cycle of the legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) in southwestern Burkina Faso

Maruca vitrata is an economically significant insect pest of cowpea in sub-Saharan Africa. Understanding the seasonal population patterns of M. vitrata is essential for the establishment of effective pest management strategies. M. vitrata larval populations on cultivated cowpea and adult flying activities were monitored in addition to scouting for host plants and parasitoids during 2 consecutive years in 2010 and 2011 in southwestern Burkina Faso. Our data suggest that M. vitrata populations overlapped on cultivated cowpea and alternate host plants during the rainy season. During the cowpea off-season, M. vitrata maintained a permanent population on the wild host plants Mucuna poggei and Daniella oliveri. The parasitoid fauna include three species, Phanerotoma leucobasis Kri., Braunsia kriegeri End. and Bracon sp. Implications of these finding for pest management strategies are discussed

An assessment of the risk of Bt-cowpea to non-target organisms in West Africa

Cowpea (Vigna unguiculata Walp.) is the most economically important legume crop in arid regions of sub-Saharan Africa. Cowpea is grown primarily by subsistence farmers who consume the leaves, pods and grain on farm or sell grain in local markets. Processed cowpea foods such as akara (a deep-fat fried fritter) are popular in the rapidly expanding urban areas. Demand far exceeds production due, in part, to a variety of insect pests including, in particular, the lepidopteran legume pod borer (LPB) Maruca vitrata. Genetically engineered Bt-cowpea, based on cry1Ab (Event 709) and cry2Ab transgenes, is being developed for use in sub-Saharan Africa to address losses from the LBP. Before environmental release of transgenic cowpeas, the Bt Cry proteins they express need to be assessed for potential effects on non-target organisms, particularly arthropods. Presented here is an assessment of the potential effects of those Cry proteins expressed in cowpea for control of LPB. Based on the history of safe use of Bt proteins, as well as the fauna associated with cultivated and wild cowpea in sub-Saharan Africa results indicate negligible effects on non-target organisms

Elevage en laboratoire de Maruca testulalis (Geyer) sur milieu artificiel simple (Lepidoptera, Pyralidae)

The authors describe the method thanks to which they successfully reared in laboratory the Pyralid pest species Maruca testulalis (Geyer), with very low death rate, the aim of this study was to product suitable entomophagous organisms.Les auteurs décrivent la méthode qui leur a permis d'élever, avec une mortalité larvaire très faible, la pyrale nuisible Maruca testulalis (Geyer), en vue de production d'entomophages appropriés.Atachi Pierre, Ahounou Mathias. Elevage en laboratoire de Maruca testulalis (Geyer) sur milieu artificiel simple (Lepidoptera, Pyralidae). In: Bulletin de la Société entomologique de France, volume 100 (1), mars 1995. pp. 25-28

Developpement de coelaenomenodera lameensis berti (coleoptera : chrysomelidae - hispinae) sur diverses provenances de palmier a huile

Des travaux conduits sur la Station de Recherche sur le Palmier à Huile de Pobè au Bénin ont permis de déterminer les facteurs physico-chimiques qui influencent la mortalité des oeufs et des larves de Coelaenomenodera lameensis sur différents croisements de palmier à huile. Les résultats obtenus ont montré que l’évolution des différents stades larvaires, des nymphes et d’adultes internes de C. lameensis est influencée par les 4 origines en comparant les populations sur Yocoboué et sur Deli et Yangambi. Le taux de mortalité des stades larvaires est plus important sur les deux Backcross (PO6271 et PO6322) que sur le C1001F. Les durées de développement des deuxième et troisième stades larvaires sont les plus affectées avec un taux de mortalité 3 à 5 fois supérieur à celui observé sur C1001F. Cette mortalité ne serait pas liée à la concentration en phénols totaux présents dans les folioles des différents croisements car le croisement Yocoboué, avec la concentration la plus élevée soit 3mg/L a présenté la plus forte sensibilité. Les attaques de C. lameensis sur lesdifférents croisements semblent être plus favorisées par les épaisseurs d’épiderme et de cuticule de la face inférieure des folioles. En effet, les plus fortes attaques ont été enregistrées sur les croisements ayant les plus faibles épaisseurs comme Yocoboué et La Mé tandis que ceux les moins attaqués (Deli, les Yangambi et les Backcross) possèdent unépiderme et une cuticule plus épais.Mots clés : Coelaenomenodera lameensis, coléoptère, Mineuse de feuille, palmier à huile, barrières physico-chimiques, Bénin