Preliminary studies of pest constraints to cotton seedlings in a direct seeding mulch-based system in Cameroon

The present study evaluated the pest constraints of an innovative crop management system in Cameroon involving conservation tillage and direct seeding mulch-based strategies. We hypothesized that the presence of mulch (i) would support a higher density of phytophagous arthropods particularly millipedes as well as pathogenic fungi that cause severe damage to cotton seedlings and (ii) would reduce early aphid infestations. The impact of two cover-crop mulches Calopogonium mucunoides and Brachiaria ruziziensis on the vigour of seedling cotton stands and arthropod damage was assessed in two independent field experiments conducted in 2001 and 2002 respectively. In both experiments the presence of mulch negatively affected cotton seedling stand by 13–14% compared to non-mulched plots and the proportion of damaged seedlings was higher in mulched than in non-mulched plots supporting the hypothesis that mulch favoured soil pest damage. In both experiments insecticidal seed dressing increased the seedling stand and the number of dead millipedes collected and fungicide had little or no effect on seedling stand and vigour. It was however observed in 2002 that the fungicide seed dressing had a positive effect on seedling stand in non-mulched plots but not in mulched plots suggesting that fungi may have been naturally inhibited by B. ruziziensis mulch. The dynamics of aphid colonization was not influenced by the presence of mulch. In 2001 taller seedlings were found in mulched than non-mulched plots probably due to greater water and nutrient availability in C. mucunoides-mulched plots than in non-mulched plot

Incidence et regulation naturelle de la chenille mineuse de l’epi de mil, Heliocheilus albipunctella de joannis (Lepidoptera, Noctuidae) a bambey dans le bassin arachidier au Senegal

Au Sénégal, la mineuse de l’épi, Heliocheilus albipunctella (Lepidoptera, Noctuidae) a commencé à causer des dégâts dans les cultures de mil suite à une longue période de sécheresse au début des années 70. Le suivi d’un réseau de 45 parcelles de producteurs à Bambey en 2013, a permis d’évaluer la situation du ravageur : abondance relative (oeuf et larve), parasitisme associé, potentiel de régulation naturelle et pertes de rendement liées aux dégâts. Les résultats ont montré une distribution très hétérogène du ravageur dans la zone avec des moyennes d’infestation des épis en oeufs de 40 % et en larves 76 %. Un taux moyen de parasitisme des oeufs par Trichogrammatoïdea sp estimé à 2 % est noté (n = 2281 oeufs). Le parasitisme larvaire est dominé par des cocons d’endoparasitoïdes de la famille des Ichneumonidae (8,6 %), des larves de Tachinidae (5,2 %) et des morphotypes non encore identifiés (4,6 %). Une faible mortalité larvaire due au Bracon sp. (1,5 %, n = 1567 larves) est observée. Ce faible taux de parasitisme, comparé au potentiel réel de la régulation naturelle observée (59 %, n = 45 parcelles) montre l’importance probable des ennemis naturels dans le contrôle du ravageur. Les pertes en grains sont estimées à 10 %.Mots clés : Heliocheilus albipunctella, mil, régulation écologique, ennemis naturels, dégât

Genetic studies of fall armyworm indicate a new introduction into Africa and identify limits to its migratory behavior

Open Access Journal; Published online: 04 Feb 2022The fall armyworm, Spodoptera frugiperda (J.E. Smith) is native to the Americas and a major pest of corn and several other crops of economic importance. The species has characteristics that make it of particular concern as an invasive pest, including broad host range, long-distance migration behavior, and a propensity for field-evolved pesticide resistance. The discovery of fall armyworm in western Africa in 2016 was followed by what was apparently a remarkably rapid spread throughout sub-Saharan Africa by 2018, causing economic damage estimated in the tens of billions USD and threatening the food security of the continent. Understanding the history of the fall armyworm invasion of Africa and the genetic composition of the African populations is critical to assessing the risk posed to different crop types, the development of effective mitigation strategies, and to make Africa less vulnerable to future invasions of migratory moth pests. This paper tested and expanded on previous studies by combining data from 22 sub-Saharan nations during the period from 2016 to 2019. The results support initial descriptions of the fall armyworm invasion, including the near absence of the strain that prefers rice, millet, and pasture grasses, while providing additional evidence that the magnitude and extent of FAW natural migration on the continent is more limited than expected. The results also show that a second entry of fall armyworm likely occurred in western Africa from a source different than that of the original introduction. These findings indicate that western Africa continues to be at high risk of future introductions of FAW, which could complicate mitigation efforts

First Record of Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae), as a Predator of the Tomato Leaf Miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), in Senegal

The recent detection in Senegal of the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and its rapid geographic spread, is a real concern for tomato production in Africa south of the Sahara. Deployment of effective biological control in the newly invaded area is urgently needed. The predatory species, Nesidiocoris tenuis (Reuter, 1895) (Heteroptera: Miridae), was collected, for the first time in Senegal, from tomato fields infested with T. absoluta. Laboratory feeding bioassay confirmed a potential of N. tenuis as a biocontrol agent of T. absoluta

Fruit flies (Diptera: Tephritidae) on vegetable crops in Reunion Island (Indian Ocean): state of knowledge, control methods and prospects for management

Significance of fruit flies in vegetable crops. Vegetable crops hold a key position in agricultural production in Reunion (Indian Ocean); however, many pests and diseases threaten the profitability of this agricultural sector. Fruit flies (Diptera: Tephritidae) figure among the main pests for solanaceous crops and cucurbits (cucumber, zucchini, melon, etc.). Losses of as much as 80% of tomato and 100% of cucurbit crop harvests have been frequently observed. Inventory and distribution. Four fruit fly species belonging to the Tephritidae family cause major damage to vegetable crops in Reunion: Bactrocera cucurbitae (Coquillet), Dacus ciliatus Loew and D. demmerezi (Bezzi) on Cucurbitaceae, and Neoceratitis cyanescens (Bezzi) on Solanaceae (primarily the tomato). Distribution of each of them is presented. Biology and behavior. A few studies on the biology and behavior of the four fruit flies were conducted in Reunion in the late 1990s. Their main biological characteristics are summarized. Population control methods used in Reunion. Various methods such as chemical control, preventive measures (sanitation), physical control, biotechnical control [colored traps, the Male Annihilation Technique (MAT) and the Bait Application Technique (BAT)], and biological control currently used in Reunion against fruit flies are reported. Other control methods such as Integrated Pest Management and the Sterile Insect Technique are not used in Reunion. Prospects for implementing agro-ecological management of vegetable fruit flies in Reunion. This part presents research actions implemented in fly bio-ecology, research actions into the genetic structure of populations and design of an agro-ecological management scheme for vegetable fruit flies. Conclusions. The control methods used independently have not been successful to effectively control tephritid populations. A more integrated approach is required, also taking into account the landscapescale and its mosaic of habitats, especially wild plants, whose role must be considered within a framework of agro-ecological management of these pest populations

Insecticide use and competition shape the genetic diversity of the aphid Aphis gossypii in a cotton-growing landscape

International audienceField populations of the cotton aphid, Aphis gossypii Glover, are structured into geographically widespread host races. In the cotton-producing regions of West and Central Africa (WCA), two genotypes have been repeatedly detected within the cotton host race, one of which (Burk1) is prevalent (>90%) and resistant to several insecticides, as opposed to the second one (Ivo). Here, we conducted whole plant and field cage experiments to test hypotheses for such low genetic diversity, including selection from insecticide treatments, interclonal competition and adaptation to host plant, or climatic conditions. To assess the genetic diversity of immigrant aphids, alatae were trapped and collected on cotton and relay host plants (okra and roselle) in the early cropping season. Individuals were genotyped at eight specific microsatellite loci and characterized by a multilocus genotype (MLG). When independently transferred from cotton (Gossypium hirustum L.) leaf discs to whole plants (G. hirsutum and G. arboreum, roselle and okra), Ivo and Burk1 performed equally well. When concurrently transferred from cotton leaf discs to the same plant species, Ivo performed better than Burk1, indicating that competition favoured Ivo. This was also the case on G. hirsutum growing outdoors. Conversely, Burk1 prevailed when cotton plants were sprayed with insecticides. In experiments where aphids were allowed to move to neighbouring plants, Burk1 was better represented than Ivo on low-populated plants, suggesting that dispersal may be a way to avoid competition on crowded plants. Most cotton aphids collected on cotton or relay host plants in the early cropping season were Burk1 (>90%), indicating high dispersal ability and, probably reflecting high frequency on host plants from which they dispersed. In the agricultural landscape of WCA, the use of broad-range insecticides on both cotton and relay host plants has led to the prevalence of one genotype of A. gossypii resistant to different classes of insecticides. Deployment of widespread and integrated pest management strategies are needed to restore cotton aphid control

Advanced Space Vehicle Design Taking into Account Multidisciplinary Couplings and Mixed Epistemic/Aleatory Uncertainties

International audienceSpace vehicle design is a complex process involving numerous disciplines such as aerodynamics, structure, propulsion and trajectory. These disciplines are tightly coupled and may involve antagonistic objectives that require the use of specific methodologies in order to assess trade-offs between the disciplines and to obtain the global optimal configuration. Generally, there are two ways to handle the system design. On the one hand, the design may be considered from a disciplinary point of view (a.k.a. Disciplinary Design Optimization): the designer of each discipline has to design its subsystem (e.g. engine) taking the interactions between its discipline and the others (interdisciplinary couplings) into account. On the other hand, the design may also be considered as a whole: the design team addresses the global architecture of the space vehicle, taking all the disciplinary design variables and constraints into account at the same time. This methodology is known as Multidisciplinary Design Optimization (MDO) and requires specific mathematical tools to handle the interdisciplinary coupling consistency. In the first part of this chapter, we present the main classical techniques to efficiently tackle the interdisciplinary coupling satisfaction problem. In particular, an MDO decomposition strategy based on the “Stage-Wise decomposition for Optimal Rocket Design” formulation is described. This method allows the design process to be decentralized according to the different subsystems (e.g. launch vehicle stages) and reduces the computational cost compared to classical MDO methods. In the first part of this chapter, we present the main classical techniques to efficiently tackle the interdisciplinary coupling satisfaction problem. In particular, an MDO decomposition strategy based on the "Stage-Wise decomposition for Optimal Rocket Design" formulation is described. This method allows the design process to be decentralized according to the different subsystems (e.g. launch vehicle stages) and reduces the computational cost compared to classical MDO methods