Spatial distribution of the cocoa mirid Sahbergella singularis Hagl. (Hemiptera: Miridae) in relation with shade, in traditional cocoa agroforestry systems

Babin Régis, Ten Hoopen Gerben Martijn, Cilas Christian, Enjalric Frank, Yédé, Gendre Pierre, Lumaret Jean Pierre. 2010. Spatial distribution of the cocoa mirid Sahbergella singularis Hagl. (Hemiptera: Miridae) in relation with shade, in traditional cocoa agroforestry systems. In : 16th International Cocoa Research Conference. Proceedings : towards rational cocoa production and efficient use ofr a sustainable world cocoa economy = 16e Conférence internationale sur la recherche cacaoyère.Actes ; 16 Conferencia Internacional de Pesquisas em Cacau. Actas ; 16 Conferencia Internacional de investigacion en cacao. Actas : vers une économie cacaoyère durable : quelles stratégies d'approche ? ; para uma produção racional de cacau e o seu uso eficiente para uma economia mundial sustentada do cacau ; hacia una produccion racional y un uso eficiente del cacao para la sustentabilitd. Lagos : Cocoa Producers' Alliance, 743-749. ISBN 978-065-959-5 Conférence Internationale sur la Recherche Cacaoyère. 16, Bali, Indonésie, 16 Novembre 2009/21 Novembre 2009.

Titre espagnol : Distribución espacial del mírido del cacao Sahlbergella singularis Hagl. (Hemiptera: Miridae) en relación con la sombra, en los sistemas agroforestales cacaoteros tradicionales / Titre français : Répartition spatiale de la miride du cacaoyer Sahlbergella Singularis Hagl. (Hemiptera: Miridae) en relation avec l'ombrage, dans les systèmes agroforestiers traditionnels à base de cacaoyers / Titre portugais : Distribución espacial del mírido del cacao Sahlbergella singularis Hagl. (Hemiptera: Miridae) en relación con la sombra, en los sistemas agroforestales cacaoteros tradicionales

Résumé : In Cameroon, cocoa (Theobroma cacao L.) is traditionally grown in thick and multi-strata agroforestry systems. In such highly diversified ecosystems, cocoa production is seriously impacted by insect pests, especially by the cocoa mirid Sahlbergella singularis. Shade regulation is an ordinary management strategy for cocoa mirids, yet very few studies were able to assess the real effect of shade on mirid populations in cocoa agroforests. The main objective of this study was the validation of shade management strategies, by measuring the impact of shade on the spatial distribution of populations of S. singularis. For two consecutive years, mirid densities were assessed by a knock-down sampling method, in three 2025 m2 plots, located in three different agroecological zones in the Centre region of Cameroon. Plot shade was characterized by the stand density, the total basal area and the crown cover of shade trees. Moreover, light conditions were assessed using hemispherical photography. Geostatistical and mapping procedures were used to display shade layout and spatial distribution of mirid populations. Populations of S. singularis were highly aggregated in the plots. Semivariance analysis and kriging visualised the spatial dependence of mirid densities. Clearly distinguishable mirid pockets of 20 to 30 adjacent infested cocoa trees were identified in two of the three plots. The high diversity of shade tree species and the large variability in density and size of shade trees resulted in a considerable heterogeneity of plot light conditions. Percentage transmitted light varied from 9.4 % to 80.1 % in the most heterogeneous plot. For two of the three plots, mirid pockets were aggregated in those areas where light transmission was highest. In the third plot, relatively high mirid densities and the presence of alternative host plant resulted in a more homogeneous distribution. For the first time, we established a quantifiable link between light intensity at cocoa canopy level and mirid density. It is not the absolute light intensity but the relative light intensity that determines the spatial distribution of mirid populations. The importance of these findings for improved mirid control is discussed. (Texte intégral)

Mots-clés Agrovoc : Theobroma cacao, Sahlbergella, agroforesterie, ombrage

Mots-clés géographiques Agrovoc : Cameroun

Mots-clés complémentaires : Sahlbergella singularis

Classification Agris : H10 - Ravageurs des plantes
F08 - Systèmes et modes de culture

Auteurs et affiliations

• Babin Régis, CIRAD-BIOS-UPR Bioagresseurs de pérennes (CMR) ORCID: 0000-0002-3753-1193
• Ten Hoopen Gerben Martijn, CIRAD-BIOS-UPR Bioagresseurs de pérennes (CMR) ORCID: 0000-0003-2133-3130
• Cilas Christian, CIRAD-BIOS-UPR Bioagresseurs de pérennes (FRA)
• Enjalric Frank, CIRAD-PERSYST-UPR Couverts permanents (MDG)
• Yédé
• Gendre Pierre, ISTOM (FRA)
• Lumaret Jean Pierre, Centre national de la recherche scientifique (FRA)

Source : Cirad - Agritrop (https://agritrop.cirad.fr/554232/)

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