Dynamique structurale des îlots de forêt claire à Anogeissus leiocarpa (DC.) Guill. et Perr. dans le Sud-Ouest du Burkina Faso

Les forêts claires résultent de la dégradation des forêts denses sèches. Elles sont soumises aux facteurs climatiques et anthropiques. Cette étude vise à analyser la diversité floristique et la  dynamique des principales espèces dans la forêt classée de Koulbi. Les données ont été collectées dans 27 placeaux de 900 m2. Le diamètre (Dbh1,30 m) >5 cm et la hauteur des individus ont été mesurés. La régénération a été comptée et l’état sanitaire apprécié. Les indices de Shannon et de Piélou, la valeur d’importance écologique de l’espèce (IVI), la densité et la surface terrière ont été calculés. La distribution de Weibull a été appliquée à la structure des principales espèces. L’indice de Shanonn = 3,01 bits montre une diversité moyenne et l’indice de Pielou = 0,49 traduit la dominance de quelques espèces. Les espèces ayant un IVI significatif sont Anogeissus leiocarpa (DC.) Guill. Et Perr. (116,19), Pterocarpus erinaceus Poir. (21,66), Lannea barteri Oliv. Engl. (13,40), Adansonia digitata L. (12,92) et Vitellaria paradoxa Gaertn. (11,80). La principale espèce, A. leiocarpa présente une bonne densité tant au niveau des adultes (316 pieds/ha) que des juvéniles (667 pieds/ha). Sa structure diamétrique en «J renversé» est synonyme d’une bonne dynamique. Cependant, elle est menacée par la mortalité (9,27%) par endroit des sujets.Mots clés : Diversité floristique, régénération, mortalité, forêt classée de Koulbi

Pession anthropique et dynamique végétale dans la Forêt Classée de Tiogo au Burkina Faso: apport de la Télédétection

Anthropogenic Pressure and Vegetation dynamics in the Classified Forest of Tiogo in Burkina Faso: Contribution of Remote Sensing. In Burkina Faso, the area of protected areas decreases yearly under the effect of anthropogenic pressure and climate change. In order to understand this extreme degradation of vegetation, a study was initiated in the Classified Forest of Tiogo. It aims at highlighting the forest dynamics between 1986 and 2014 using remote sensing and geographic information systems. To do this, Landsat images of 1986 and 2014 were analysed. Digital processing of satellite images was coupled with floristic data (dendrometric data) collected on the field. This allowed to identify gallery forests, wooded savannas (dense and clear), shrubby savannas (dense and clear) and fields. The cartographic results reveal a regression of forest canopy of about 0.49% per year between 1986 and 2014. This regression of vegetation is made to the benefit of agricultural fields that have increased by 3,347 ha. These results suggest the development of an effective policy of sustainable management of Tiogo Forest to prevent its disappearance in the medium term

Rhizosphere microbiota interfers with plant-plant interactions

Diversity, structure and productivity of above-ground compartment of terrestrial ecosystems have been generally considered as the main drivers of the relationships between diversity and ecosystem functioning. More recently it has been suggested that plant population dynamics may be linked with the development of the below-ground community. The biologically active soil zone where root-root and root-microbe communications occur is named "Rhizosphere" where root exudates play active roles in regulating rhizosphere interactions. Root exudation can regulate the soil microbial community, withstand herbivory, facilitate beneficial symbioses, modify the chemical and physical soil properties and inhibit the growth of competing plant species. In this review, we explore the current knowledge assessing the importance of root exudates in plant interactions, in communications between parasitic plants and their hosts and how some soil microbial components could regulate plant species coexistence and change relationships between plants. This review will be focussed on several well documented biological processes regulating plant-plant communications such as exotic plant species invasions, negative root-root communication (allelopathy) and parasitic plant / host plant interactions and how some soil microbial components can interfere with signal traffic between roots. The reported data show that the overall effect of one plant to another results from multiple interacting mechanisms where soil microbiota can be considered as a key component

Biological activity and persistence of four essential oils towards the main pest of stored cowpeas, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

International audienceThe use of essential oils extracted from native aromatic plants is perceived as a promising alternative to protect stored cowpeas in West Africa. However the optimal conditions for their efficiency remain to be determined. A study was therefore carried out to compare the biological activity and temperature-related persistence of four selected essential oils towards Callosobruchus maculatus, the main pest of stored cowpeas. Essential oil extracted from Ocimum americanum proved to be very toxic towards C. maculatus adults (LC50 = 0.23 μl/l) while the oils from Hyptis suaveolens, Hyptis spicigera and Lippia multiflora exhibited higher LC50 values (1.30 μl/l; 5.53 μl/l and 6.44 μl/l respectively). The persistence of the biological activity of the four oils was variable and that from O. americanum was most persistent. Fourteen days post-application, this oil was still as active on C. maculatus adults as it was immediately after its application. Exposure of this oil to a high temperature, close to temperatures occurring during storage in Burkina Faso in the dry season, however, resulted in a rapid decrease in its efficacy. Our results emphasize the need to take into account environmental factors such as temperature to optimize the use of promising essential oils for controlling stored-product pests in West Africa

Influence of host origin on host choice of the parasitoid [i]Dinarmus basalis[/i]: Does upbringing influence choices later in life?

International audienceThe aim of this study was to investigate the influence of volatile compounds from four secondary host plants on the ability of [i]Dinarmus basalis[/i] Rond. (Hymenoptera: Pteromalidae) to locate, recognize, and parasitize its host, 4th instar larvae or pupae of [i]Callosobruchus maculatus[/i] F. ([i]Coleoptera: Chrysomelidae[/i]). To examine this, strains of [i]D. basalis[/i] were transferred from cowpea seeds [i](Vigna unguiculata[/i] (L.) Walp. (Fabales: [i]Fabaceae[/i])) to pigeon pea ([i]Cajanus cajan[/i] (L.) Millsp.) and two varieties of Bambara groundnut ([i]Vigna subterranea[/i] (L.) Verdc.) seeds. The ability of D. [i]basalis[/i] females to recognize the volatile compounds emanating from their complex host plant was tested by using a Y-tube olfactometer and a three-dimensional device. The results suggest that when females have a choice between pure air and the air emanating from their complex host of origin, they are attracted to the air tainted by the volatile compounds they have become accustomed to. They spent significantly more time (p < 0.0001) in the branch of the tube leading to the odorous air than in the tube leading to the pure air. When females from pigeon pea seed hosts were offered a choice between cowpea and pigeon pea seeds, all containing 4th instar larvae, the familiar odor of pigeon pea seeds were most attractive. When females from Bambara groundnut (white and striped) seed hosts were offered a choice between cowpea and pigeon pea seeds, all containing 4th instar larvae, they were significantly attracted to the odour of cowpea seeds. In the three-dimensional system, the females from the four strains did not appear to have any preference for a given type of seed containing 4th instar larvae or pupae. The parasitism rate remained high on all four types of seeds used. These results show that the use of D. [i]basalis[/i] as a biological control agent is possible in host changing situations where C. maculatus starts to attack other legumes. The results of this study also provide information supporting the behavioral plasticity of D. [i]basalis[/i]. Understanding the mechanisms involved in the adaptive phenomena of biological control agents is discussed in the context of the development of adequate methods of pest control