Host-feeding patterns of Aedes (Aedimorphus) vexans arabiensis, a Rift Valley Fever virus vector in the Ferlo pastoral ecosystem of Senegal

Background: Host-vector contact is a key factor in vectorial capacity assessment and thus the transmission of mosquito-borne viruses such as Rift Valley Fever (RVF), an emerging zoonotic disease of interest in West Africa. The knowledge of the host-feeding patterns of vector species constitutes a key element in the assessment of their epidemiological importance in a given environment. The aim of this work was to identify the blood meal origins of the mosquito Aedes vexans arabiensis, the main vector of RVF virus in the Ferlo pastoral ecosystem of Senegal. Methodology/principal findings: Engorged female mosquitoes were collected in Younoufe´re´ in the pastoral ecosystem in the Ferlo region during the 2014 rainy season. CO2-baited CDC light traps were set at six points for two consecutive nights every month from July to November. Domestic animals present around traps were identified and counted for each trapping session. Blood meal sources of engorged mosquitoes were identified using a vertebrate-specific multiplexed primer set based on cytochrome b. Blood meal sources were successfully identified for 319 out of 416 blood-fed females (76.68%), of which 163 (51.1%) were single meals, 146 (45.77%) mixed meals from two different hosts and 10 (3.13%) mixed meals from three different hosts. Aedes vexans arabiensis fed preferentially on mammals especially on horse compared to other hosts (FR = 46.83). Proportions of single and mixed meals showed significant temporal and spatial variations according to the availability of the hosts. Conclusion: Aedes vexans arabiensis shows an opportunistic feeding behavior depending on the host availability. This species fed preferentially on mammals especially on horses (primary hosts) and ruminants (secondary hosts)

A model-based approach to assess the effectiveness of pest biocontrol by natural enemies

Main goal: The aim of this note is to propose a modeling approach for assessing the effectiveness of pest biocontrol by natural enemies in diversified agricultural landscapes including several pesticide-based management strategies. Our approach combines a stochastic landscape model with a spatially-explicit model of population dynamics. It enables us to analyze the effect of the landscape composition (proportion of semi-natural habitat, non-treated crops, slightly treated crops and conventionally treated crops) on the effectiveness of pest biocontrol. Effectiveness is measured through environmental and agronomical descriptors, measuring respectively the impact of the pesticides on the environment and the average agronomic productivity of the whole landscape taking into account losses caused by pests. Conclusions: The effectiveness of the pesticide, the intensity of the treatment and the pest intrinsic growth rate are found to be the main drivers of landscape productivity. The loss in productivity due to a reduced use of pesticide can be partly compensated by biocontrol. However, the model suggests that it is not possible to maintain a constant level of productivity while reducing the use of pesticides, even with highly efficient natural enemies. Fragmentation of the semi-natural habitats and increased crop rotation tend to slightly enhance the effectiveness of biocontrol but have a marginal effect compared to the predation rate by natural enemies. This note was written in the framework of the ANR project PEERLESS "Predictive Ecological Engineering for Landscape Ecosystem Services and Sustainability"(ANR-12-AGRO-0006)

Etude Phénotypique des Taurins Ndama du Centre de Recherches Zootechniques de Kolda (Sénégal)

Au Sud du Sénégal, du fait de la présence de glossines, le taurin Ndama ou Bos taurus taurus est la principale race bovine élevée par les agropasteurs. L’importance indéniable de ces bovins dans la vie socio-économique a conduit à la création du Centre de Recherches zootechniques de Kolda (CRZ-K) et l’initiation d’un programme de sélection à noyau fermé dès 1972 pour améliorer les performances des taurins. L’actuel noyau de sélection ouvert est constitué par des animaux appartenant au CRZ-K et ceux de la Coopérative des Agro-éleveurs Sélectionneurs de la Ndama (CASE-Ndama). L’objectif de cette étude est de caractériser phénotypiquement les taurins Ndama du noyau de sélection. La collecte des données phénotypiques composées de 15 variables qualitatives et 17 quantitatives a été réalisée sur 118 taurins adultes agés d’au moins quatre ans. L’évaluation des performances pondérales a été réalisée grâce à l’analyse des données longitudinales de 1970 bovins durant la période de 1973 à 2016. Les variables qualitatives ont été exprimées en pourcentages et pour les variables quantitatives, une analyse descriptive et une comparaison des moyennes ont été faites. Les résultats ont montré que la majorité des animaux présentait la même apparence avec une robe fauve uniforme, des cornes bicolores en lyre, des muqueuses peu pigmentées. Avec un dimorphisme marqué chez les bovins, les animaux adultes ont une hauteur au garrot moyenne de 106,9 ± 3,5 cm et un poids moyen de 230,9 ± 40,6 kg. Les moyennes de la longueur du corps et du périmètre thoracique étaient de 112,0 ± 7,9 cm et 150,0 ± 8,4 cm respectivement. Cette étude tout en montrant la hausse des mensurations corporelles des animaux par rapport à leurs congénères élevés dans les exploitations rurales souligne la baisse des performances pondérales survenue pendant certaines périodes durant lesquelles le programme a connu des contraintes. In southern Senegal, because of tsetse flies, Ndama taurine or Bos taurus taurus is the main bovine breed raised by farmers. The undeniable importance of these cattle in the socio-economic life led to the creation of the Centre de Recherches Zootechniques of Kolda (CRZ-K) and the initiation of a selection program since 1972 to improve animal productivity. The current open breeding nucleus is composed by animals belonging to the CRZ-K and those of farmers Ndama Agro-Breeders' Cooperative (CASE-Ndama). The aim of this study is to phenotypically characterize Ndama taurins of the selection nucleus. The phenotypic data collected for 15 qualitative and 17 quantitative variables was carried out on 118 adult bulls at least four years old. Longitudinal data from 1970 cattle during the period 1973 to 2016 were used to evaluate weight performances. The results showed that the majority of animals had the same appearance with a uniform fawn color, black and white lyre horns and fairly pigmented mucous membranes. Sexual dimorphism was marked. Adult animals had an average height of 106.9 ± 3.5 cm and average weight of 230.9 ± 40.6 kg. The mean of body length and chest perimeter were 112.0 ± 7.9 cm and 150.0 ± 8.4 cm respectively. This study showed the increase in body measurements of animals compared to those in rural farms and highlighted the decline in weight performances occurred during certain periods where the program had constraints

Animal trypanosomosis eliminated in a major livestock production region in Senegal following the eradication of a tsetse population

African animal trypanosomosis (AAT) was one of the main disease-related constraints to the development of intensive livestock production systems in the Niayes region of Senegal, a 30 km wide strip of land along the coast between Dakar and Saint-Louis. To overcome this constraint, the Government of Senegal initiated an area-wide integrated pest management programme combining chemical control tactics with the sterile insect technique to eradicate a population of the tsetse fly Glossina palpalis gambiensis Vanderplank, 1949 (Diptera, Glossinidae) in this area. The project was implemented following a phased conditional approach, and the target area was divided into three blocks treated sequentially. This study aims to assess the temporal dynamics of the prevalence of Trypanosoma spp. during the implementation of this programme. Between 2009 and 2022, 4,359 blood samples were collected from cattle and screened for trypanosomes using both the buffy coat and ELISA techniques, and PCR tests since 2020. The seroprevalence decreased from 18.9% (95%CI: 11.2–26.5) in 2009 to 0% in 2017–2022 in block 1, and from 92.9% (95%CI: 88.2–97) in 2010 to 0% in 2021 in block 2. The parasitological and serological data confirm the entomological monitoring results, i.e., that there is a high probability that the population of G. p. gambiensis has been eradicated from the Niayes and that the transmission of AAT has been interrupted in the treated area. These results indicate the effectiveness of the adopted approach and show that AAT can be sustainably removed through the creation of a zone free of G. p. gambiensis

Understanding flying insect dispersion: Multiscale analyses of fragmented landscapes

International audienceA multiscale model was developed to simulate the rate of landing of a winged insect, the grain aphid, Sitobion avenae F. At a large scale (kilometric scale), it is convenient to use a deterministic model of their dispersion, based upon diffusion-advection-reaction partial derivative equations. At a small scale (hectometric scale), the process of site selection ('landing') is only partially understood, but is known to include the perception of field colour and landscape characteristics. Several hypotheses on aphids' behaviour were tested to simulate the rate of landing: the simulation was done by a cellular automata submodel under five different hypotheses on the precise organisation of the landing behaviour. We found a strong interaction between the effect of the proportion of wheat crops in the landscape and their spatial organisation. The spatial correlation between the places occupied by wheat crops appears crucial to determine the global rate of landing of the aerial insect stock. The shape of the response surface of landing rate against the proportion of surface occupied by wheat, and the spatial autocorrelation of wheat plots, appears very regular and relatively simple to model by ad hoc mathematical functions. Large scale simulations using the results of the small scale model in a diffusion-reaction equation solved numerically, showed that, on a real landscape extracted from a GIS on the whole Brittany region (western France), the spatial pattern of the aphid landing is sensitive to the hypothesis tested on their landing behaviour. This hierarchical modelling combining two different approaches at two different scales (mathematical deterministic equations on a large multi-kilometric scale, and partly stochastic cellular automata on a small hectometric scale), requires methods to validate its results in the field, in the framework of a decision support system. Such amultiscalemodel has a wide field of application including not only plant protection but also management and conservancy of animal species dispersing by flight

A spatiotemporal model for predicting grain aphid population dynamics and optimizing insecticide sprays at the scale of continental France

International audienceWe expose here a detailed spatially explicit model of aphid population dynamics at the scale of a whole country (Metropolitan France). It is based on convection-diffusionreaction equations, driven by abiotic and biotic factors. The target species is the grain aphid, Sitobion avenae F., considering both its winged and apterousmorphs. In this preliminary work, simulations for year 2004 (an outbreak case) produced realistic aphid densities, and showed that both spatial and temporal S. avenae population dynamics can be represented as an irregular wave of population peak densities from southwest to northeast of the country, driven by gradients or differences in temperature, wheat phenology, and wheat surfaces. This wave pattern fits well to our knowledge of S. avenae phenology. The effects of three insecticide spray regimes were simulated in five different sites and showed that insecticide sprays were ineffective in terms of yield increase after wheat flowering. After suitable validation, which will require some further years of observations, the model will be used to forecast aphid densities in real time at any date or growth stage of the crop anywhere in the country. It will be the backbone of a decision support system, forecasting yield losses at the level of a field. The model intends then to complete the punctual forecasting provided by older models by a comprehensive spatial view on a large area and leads to the diminution of insecticide sprayings in wheat crops

A model-based approach to assess the effectiveness of pest biocontrol by natural enemies

The aim of this note is to propose a modeling approach for assessing the effectiveness of pest biocontrol by natural enemies in diversified agricultural landscapes including several pesticide-based management strategies. Our approach combines a stochastic landscape model with a spatially-explicit model of population dynamics. It enables us to analyze the effect of the landscape composition (proportion of semi-natural habitat, non-treated crops, slightly treated crops and conventionally treated crops) on the effectiveness of pest biocontrol. Effectiveness is measured through environmental and agronomical descriptors, measuring respectively the impact of the pesticides on the environment and the average agronomic productivity of the whole landscape taking into account losses caused by pests.The effectiveness of the pesticide, the intensity of the treatment and the pest intrinsic growth rate are found to be the main drivers of landscape productivity. The loss in productivity due to a reduced use of pesticide can be partly compensated by biocontrol. However, the model suggests that it is not possible to maintain a constant level of productivity while reducing the use of pesticides, even with highly efficient natural enemies. Fragmentation of the semi-natural habitats and increased crop rotation tend to slightly enhance the effectiveness of biocontrol but have a marginal effect compared to the predation rate by natural enemies

Response of insect relative growth rate to temperature and host-plant phenology: estimation and validation from field data.

Between 1975 to 2011, aphid Relative Growth Rates (RGR) were modelled as a function of mean outdoor temperature and host plant phenology. The model was applied to the grain aphid Sitobion avenae using data on aphid counts in winter wheat at two different climate regions in France (oceanic climate, Rennes (western France); continental climate, Paris). Mean observed aphid RGR was higher in Paris compared to the Rennes region. RGR increased with mean temperature, which is explained by aphid reproduction, growth and development being dependent on ambient temperature. From the stem extension to the heading stage in wheat, there was either a plateau in RGR values (Rennes) or an increase with a maximum at heading (Paris) due to high intrinsic rates of increase in aphids and also to aphid immigration. From the wheat flowering to the ripening stage, RGR decreased in both regions due to the low intrinsic rate of increase in aphids and high emigration rate linked to reduced nutrient quality in maturing wheat. The model validation process showed that the fitted models have more predictive power in the Paris region than in the Rennes region