122418 research outputs found
Sort by
Distribution of larval habitats and efficiency of various trap settings to monitor sympatric Aedes albopictus and Aedes aegypti in La Reunion
Get PDFTo prepare for a boosted sterile insect technique (SIT) field trial in Saint-Joseph, Reunion island, we compared the attractiveness of two adult mosquito traps for Aedes albopictus and Aedes aegypti. In addition, we explored the co-occurrence of these species in their usual larval habitats. Two traps were compared with two conditions each using a Latin square design: BG Sentinel trap baited with carbon dioxide (CO2) with/without addition of BG Lure and ovi-sticky trap with/without hay. The ovi-sticky traps proved ineffective. For both Aedes species, CO2-baited traps were equally effective at catching females when baited with the lure or not. In contrast, they were more attractive to males than for females with the lure. Aedes aegypti larvae were found in four of six vacoas (Pandanus utilis), and one of four anthropogenic breeding sites. In vacoas, the densities of Aedes albopictus and Aedes aegypti larvae were negatively correlated, whereas the correlation was positive between chironomids and Aedes aegypti. The abundance of adults and larvae varied according to weather conditions. Finally, CO2-baited traps were used without lure for the entomological monitoring to assess the effectiveness of the area-wide boosted SIT intervention to reduce costs and logistics
Cacao stand rehabilitation practices affect long-term cocoa production in agroforestry systems in Cameroon
Get PDFPrevious studies suggest that the density and diversity of associated trees stabilises cocoa agroforestry systems (cAFS) production in the long term. However, the impact of cocoa rejuvenation practices on this stabilisation process remains unclear. This study investigated how farmers' practices, particularly cocoa stand management, influence long-term cocoa yields, considering the production area's history and current management. Cocoa plantations aged from 7 to over 60 years were selected in two areas: an old cocoa production area (Bakoa) and a cocoa pioneer front in the forested land (Talba) in Cameroon's Centre region. Measurements included cocoa and associated tree diameters, shade tree cover and accessible cocoa yield. We also identified architectural types of cocoa trees representing various development stages. Results showed no effect of plantation age on associated tree parameters at either site. In Talba, cocoa tree density and accessible yield decreased with plantation age. This decline was associated with an increase in senescent cocoa trees and few regenerated multi-stem trees over time. This indicates poor rejuvenation of existing plantations in Talba, where forest reserves are available to create new ones. Conversely, in Bakoa, an area with no available forest reserves, rejuvenation of existing plantations, evidenced by the increasing density of multi-stem cocoa trees and new seedlings over time, was associated with stable yields in the long term. Providing farmers with training and incentives to rejuvenate old cocoa stands should be part of an overall strategy to increase production, improve farmers' incomes, protect forests and comply with the commercial rules of consumer countries
Identifying reservoirs hosting Eldana saccharina (Lepidoptera: Pyralidae), a pest of sugarcane in Senegal
No full textThe Senegal River Delta Valley is characterized by flat ground, high daily temperatures, and a short rainy season. In Richard Toll, the Compagnie Sucrière du Sénégal (CSS) grows 12,000 ha of sugarcane but suffers with variability of pest infestation among years. In this area, wherever the soil surface is moist enough, it is favourable to the development of natural vegetation. This dynamic led to a question as to whether this spontaneous natural vegetation can host key pests such as the sugarcane borer, Eldana saccharina Walker. Potential host plant species were first listed using the Decision Support System DECIPEST. Then, sites with a sufficient density of potential host plants were identified using drone images taken at a 100-m height over the farmland and its edges at three periods of the year (middle of the dry season, beginning of the rainy season, end of the rainy season). Preliminary results suggest that a potential E. saccharina host at CSS is Typha domingensis located in the water collection drains and the water tanks
Multiyear drought strengthens positive and negative functional diversity effects on tree growth response
Get PDFMixed-species forests are proposed to enhance tree resistance and resilience to drought. However, growing evidence shows that tree species richness does not consistently improve tree growth responses to drought. The underlying mechanisms remain uncertain, especially under unprecedented multiyear droughts. We used a network of planted tree diversity experiments to investigate how neighborhood tree diversity and species' functional traits influence individual tree responses to drought. We analyzed tree cores (948 trees across 16 species) from nine young experiments across Europe featuring tree species richness gradients (1–6 species), which experienced recent severe droughts. Radial growth response to drought was quantified as tree-ring biomass increment using X-ray computed tomography. We applied hydraulic trait-based growth models to analyze single-year drought responses across all sites and site-specific responses during consecutive drought years. Growth responses to a single-year drought were partially explained by the focal species' hydraulic safety margin (representing species' drought tolerance) and drought intensity, but were independent of neighborhood species richness. The effects of neighborhood functional diversity on growth responses shifted from positive to negative with increasing drought duration during a single growing season. Tree diversity effects on growth responses strengthened during consecutive drought years and were site-specific with contrasting directions (both positive and negative). This indicates opposing diversity effects pathways under consecutive drought events, possibly resulting from competitive release or greater water consumption in diverse mixtures. We conclude that tree diversity effects on growth under single-year droughts may differ considerably from responses to consecutive drought years. Our study highlights the need to consider trait-based approaches (specifically, hydraulic traits) and neighborhood scale processes to understand the multifaceted responses of tree mixtures under prolonged drought stress. This experimental approach provides a robust framework to test biodiversity-ecosystem functioning (BEF) relationships relevant for young, planted forests under increased drought stress
Marché européen de la banane. La banane dollar se taille la part du lion
No full textL'approvisionnement de l'UE27 en banane dessert progresse fortement en 2024. Le taux de croissance est de 3.7 %, pour atteindre un volume net (réexportations décomptées) de 5 989 000 tonnes. Après les années 2021 et 2022 où l'approvisionnement a baissé, 2023 et 2024 ont vu une augmentation des mises en marché de 421 000 tonnes. Ce chiffre traduit la vitalité du marché européen post-Covid. Les effets, notamment sur le prix des matières premières, de l'agression russe sur son voisin ukrainien, les perturbations logistiques (passage des canaux, retards logistiques, difficulté à repositionner les conteneurs, grèves portuaires, etc.) et bien évidemment les effets tangibles du changement climatique dans nombre de pays producteurs n'ont paradoxalement pas eu d'impacts dépressifs sur les flux de banane dédiés au marché de l'UE. En revanche, on peut dire que ces événements continuent de déstabiliser grandement les chaînes d'approvisionnement. Si la tendance globale est donc fortement haussière, l'analyse par groupe d'origines montre de notables différences
Transcriptomic analysis reveals genetic factors underlying impaired symbiotic nitrogen fixation in lines derived from crosses between cultivated peanut (Arachis hypogaea L.) and its wild ancestors
Get PDFBackground : Symbiotic nitrogen fixation (SNF) is a complex process regulated by numerous genes extensively studied in legumes that undergo intracellular infection, such as Lotus japonicus, Medicago truncatula, and Glycine max. However, the molecular and genetic mechanisms of SNF in legumes that rely on the intercellular infection pathway, such as peanut (Arachis hypogaea L.), remain poorly understood. In a previous study, we identified two chromosome segment substitution lines (CSSLs), 12CS_051 and 12CS_044, each contains a wild segment on homeologous regions of chromosomes A02 and B02 respectively, that are severely impaired in nitrogen fixation. In this study, we have compared the transcriptomes of those lines with that of their recurrent parent, Fleur11, in roots inoculated with the effective Bradyrhizobium vignae strain ISRA400 to identify candidate genes associated with the reduced nitrogen fixation observed in these CSSLs. Results : A comparative analysis of the transcriptome profiles of the CSSLs and Fleur11 revealed significant changes in the expression of genes involved in plant immune signaling and key symbiotic genes, such as NIN, EFD, FEN1 or SNF-related transporters. These results align with the phenotypic differences observed during the symbiotic process in the CSSLs. When focusing on each QTL region, we found that only the orthologs of the symbiotic gene FEN1, which is responsible for the failure in the enlargement of infected cells in L. japonicus, exhibited a lack of expression in the two CSSLs compared to Fleur11. FEN1 encodes a homocitrate synthase that is essential for the nitrogenase activity. We hypothesize that changes in the expression of FEN1 could affect the nitrogenase activity, potentially leading to the unfair SNF observed in these lines. Conclusions : In this study, we analyzed the expression profiles of two ineffective nitrogen-fixing chromosome segment substitution lines and identified FEN1 as a suitable candidate gene involved in peanut symbiosis. This research provides valuable insights into understanding and improving SNF in peanut
Formation à la méthode d'enquête 12mo, à l'analyse et l'interprétation des données de productivité - Mission Tchad du 31/03/2025 au 14/04/2025
No full textUsing a low-cost drone to assess herbaceous biomass and quality in the Sahelian Rangeland ecosystems
Get PDFExisting ways of assessing rangeland plant biomass and nutritional quality mostly rely on field surveys, which are difficult to generalise across plots, along with laboratory-based techniques that entail lengthy pre-processing procedures. As a solution, drones have emerged as a promising tool capable of collecting low-altitude images over expansive areas with minimal effort and cost. Here, we explore the potential of low-cost drone images to estimate the rangeland biomass, and quality of the Sahelian rangeland ecosystem. Model calibration and validation were conducted using a random forest machine learning algorithm, where the response variables were field vegetation samples, and the explanatory variables were derived from drone image outputs. A principal component analysis (PCA) was conducted to explore the multivariate relationships between drone-derived vegetation indices and field-measured biomass and quality attributes. In the validation datasets, the random forest model exhibited relative root mean squared errors (RRMSE) of 31% for fresh mass and 37% for dry mass. The random forest model demonstrated a relatively high prediction accuracy, yielding RRMSE values of 32% for crude protein, 9% for neutral detergent fibre, 8% for acid detergent fibre, and 17% for organic matter digestibility contents. The PCA revealed that the first two components explained 53.3% of the total variance. Overall, these results showed that red, green and blue (RGB) images acquired from low-cost drones can be used to estimate rangeland biomass and quality
Diversity and profitability of oil palm smallholders in the southeastern Mexican states of Campeche and Tabasco
Get PDFSmallholders in southeastern Mexico face significant pedoclimatic constraints, including an uneven annual rainfall distribution and poorly workable soils. Consequently, they originally focused on extensive cattle rearing and food crops. Oil palm cultivation was introduced in the states of Campeche and Tabasco in the late 1990s via a federal rural development programme targeting family farmers. This article examines how smallholders have adopted oil palm cultivation and assesses the economic impacts of this shift. Technical-economic surveys were conducted in these states involving 47 oil palm producers and 8 interested farmers. Coexisting with agro-industrial estates and large cattle farms in the process of diversification, we differentiated two main types of smallholders: those specialising in oil palm cultivation and larger producers (>50 ha) who diversified into oil palm while remaining cattle ranchers. Our results show that oil palm cultivation is economically more attractive than alternatives such as cattle rearing, maize cultivation or agricultural wage labour. The study area can be divided into three agroecological zones with varying palm oil production potentials, influencing technical practices and economic performance. We identified three types of oil palm cropping systems based on input and labour use: the “extensive”, the “intermediate”, and the “intensive” ones. In a context of volatile palm oil prices, our results indicate that the “intermediate” system yielded the highest labour and per-hectare productivity, in all agroecological zones. All smallholder oil palm farms generated high revenues and positive cash balances, enabling self-financed expansion of at least two hectares annually