Evaluation de l’efficacité d’un bio-fongicide à base de Lecanicillium lecanii (Zimmerm) sur les cercosporioses de l’arachide (Arachis hypogaea L.) en milieu réel

La lutte biologique est une méthode alternative à la lutte chimique ayant des effets néfastes sur la santé des producteurs, des consommateurs et de l’environnement. Les maladies foliaires, en l’occurrence les cercosporioses causées par Cercospora arachidicola et Phaeoisariopsis personata handicapent la production arachidière dans le monde en général, et particulièrement au Burkina Faso. Cette étude a consisté à utiliser une souche A de Lecanicillium lecanii, à des traitements différents contre le développement des cercosporioses. Pour ce faire, quatre traitements, T1, T2, T3 et T4, ont été appliqués sur deux variétés, la TS32-1 et la PC79-79 respectivement chaque deux jour, chaque semaine, chaque dix jour et chaque deux semaine. Le dispositif expérimental est un bloc de Fisher complètement randomisé à trois répétitions, constituée chacune de 5 blocs dont 4 blocs correspondant chacun à un traitement et un bloc constituant le témoin. L’étude, conduite à Gampèla, au Burkina Faso a permis de mesurer les paramètres tels que la levée au 21ème JAS, la densité de peuplement au 32ème JAS, l’incidence des cercosporioses et l’envahissement foliaire, le taux de survie, le pourcentage de défoliation et les composantes de rendement. L’étude a permis de montrer que les traitements ont eu un effet réductif sur le développement des cercosporioses au niveau des deux variétés, surtout sur la variété sensible TS32-1. Le traitement effectué chaque deux jour a donné le meilleur contrôle des cercosporioses avec une note moyenne de 3,5 sur TS32- 1 et de 2,75 sur PC79-79. Sur les composantes du rendement, les traitements ont également permis d’obtenir de bons résultats comparés aux résultats du témoin pour les deux variétés. En effet, le témoin a enregistré de 318,7 et 402,3 kg/ha respectivement pour les variétés TS32-1 et PC79-79 et les autres traitements ont obtenu des rendements compris entre 507,7 et 1656,7 kg/ha. Biological control is an alternative method to chemical control, which has adverse effects on the health of producers, consumers and the environment. Foliar diseases, in this case cercosporioses caused by Cercospora arachidicola and Phaeoisariopsis personata, handicap peanut production in the world in general, and particularly in Burkina Faso. This study consisted in using a Lecanicillium lecanii strain A, with different treatments against the development of cercosporioses. To do this, four treatments, T1, T2, T3 and T4, were applied to two varieties, TS32-1 and PC79-79 respectively every two days, every week, every ten days and every two weeks. The experimental set-up was a completely randomised Fisher block with three replicates, each consisting of five blocks, four of which corresponded to a treatment and one to a control. The study, conducted in Gampèla, Burkina Faso, measured parameters such as emergence at 21 days after planting, stand density at 32 days after planting, incidence of cercosporiosis and leaf invasion, survival rate, defoliation percentage and yield components. The study showed that the treatments had a reducing effect on cercosporium development in both varieties, especially in the susceptible variety TS32-1. The treatment applied every second day gave the best cercospora control with an average score of 3.5 on TS32-1 and 2.75 on PC79- 79. On the output components, the treatments also performed well compared to the control for both varieties. Indeed, the control recorded 318.7 and 402.3 kg/ha for TS32-1 and PC79-79 respectively and the other treatments obtained yields between 507.7 and 1656.7 kg/ha

Methods to collect Anopheles mosquitoes and evaluate malaria transmission: A comparative study in two villages in Senegal

<p>Abstract</p> <p>Background</p> <p>Various methods have been studied as replacement of human landing catches (HLC) for mosquito sampling in entomological studies on malaria transmission. Conflicting results have been obtained in comparing relative efficiency of alternative methods, according to the area, the species present and their density. The aim of this study was to compare the number and characteristics of mosquitoes sampled in two areas of Senegal by three different methods: HLC, light traps adjacent to an occupied bed net (LT/N), pyrethrum spray catches (PSC).</p> <p>Methods</p> <p>Collections were performed in two villages: Dielmo (Soudan savanna) and Bandafassi (Soudan Guinean savanna), two or three nights per month for a 4-5 months period during the maximal transmission season in 2001-2002. Species were identified and <it>Plasmodium </it>infection determined by ELISA. The specific composition, circumsporozoite protein rate and entomological inoculation rate were calculated.</p> <p>Results</p> <p>The diversity of mosquito species captured was maximal with LT/N, minimal with PSC. The mean number of anopheles captures each night was significantly different according to the method used and the species. PSC displayed a significantly lower anopheles density. HLC was the most efficient sampling method when <it>Anopheles gambiae </it>was the main vector (in Bandafassi); LT/N when it was <it>Anopheles funestus </it>(in Dielmo). A significant correlation was found between HLC and LT/M but correlation parameters were different according to the species. Circumsporozoite protein rates were not significantly different between methods or species. The entomological inoculation rate varied along with vector density and thus with methods and species.</p> <p>Conclusions</p> <p>The choice of sampling method influenced entomological data recorded. Therefore, the sampling technique has to be chosen according to the vector studied and the aim of the study. Only HLC must be considered as the reference method, but in some conditions LT/N can be used as an alternative method.</p

Dynamics of transmission of Plasmodium falciparum by Anopheles arabiensis and the molecular forms M and S of Anopheles gambiae in Dielmo, Senegal

<p>Abstract</p> <p>Background</p> <p>The adaptation of <it>Anopheles gambiae </it>to humans and its environment involves an ongoing speciation process that can be best demonstrated by the existence of various chromosomal forms adapted to different environments and of two molecular forms known as incipient taxonomic units.</p> <p>Methods</p> <p>The aim of this study was to compare the epidemiologic role of <it>Anopheles arabiens </it>is and the molecular forms M and S of <it>Anopheles gambiae </it>in the transmission of Plasmodium in a rural areas of southern Senegal, Dielmo. The sampling of mosquitoes was carried out monthly between July and December 2004, during the rainy season, by human volunteers and pyrethrum spray catches.</p> <p>Results</p> <p><it>Anopheles arabiensis</it>, <it>An. gambiae </it>M and S forms coexisted during the rainy season with a predominance of the M form in September and the peak of density being observed in August for the S form. Similar parity rates were observed in <it>An. arabiensis </it>[70.9%] (n = 86), <it>An</it>. <it>gambiae </it>M form [68.7%] (n = 64) and <it>An</it>. <it>gambiae </it>S form [81.1%] (n = 156). The circumsporozoite protein (CSP) rates were 2.82% (n = 177), 3.17% (n = 315) and 3.45% (n = 405), with the mean anthropophilic rates being 71.4% (n = 14), 86.3% (n = 22) and 91.6% (n = 24) respectively for <it>An</it>. <it>arabiensis </it>and <it>An</it>. <it>gambiae </it>M and S forms. No significant difference was observed either in host preference or in <it>Plasmodium falciparum </it>infection rates between sympatric M and S populations.</p> <p>Conclusion</p> <p>No difference was observed either in host preference or in <it>Plasmodium falciparum </it>infection rates between sympatric M and S populations, but they present different dynamics of population. These variations are probably attributable to different breeding conditions.</p

Comparative susceptibility to <it>Plasmodium falciparum </it>of the molecular forms M and S of <it>Anopheles gambiae </it>and <it>Anopheles arabiensis</it>

<p>Abstract</p> <p>Background</p> <p>The different taxa belonging to <it>Anopheles gambiae </it>complex display phenotypic differences that may impact their contribution to malaria transmission. More specifically, their susceptibility to infection, resulting from a co-evolution between parasite and vector, might be different. The aim of this study was to compare the susceptibility of M and S molecular forms of <it>Anopheles gambiae </it>and <it>Anopheles arabiensis </it>to infection by <it>Plasmodium falciparum</it>.</p> <p>Methods</p> <p>F3 progenies of <it>Anopheles gambiae s.l</it>. collected in Senegal were infected, using direct membrane feeding, with <it>P. falciparum </it>gametocyte-containing blood sampled on volunteer patients. The presence of oocysts was determined by light microscopy after 7 days, and the presence of sporozoite by ELISA after 14 days. Mosquito species and molecular forms were identified by PCR.</p> <p>Results</p> <p>The oocyst rate was significantly higher in the molecular S form (79.07%) than in the M form (57.81%, Fisher's exact test p < 0.001) and in <it>Anopheles arabiensis </it>(55.38%, Fisher's exact test vs. S group p < 0.001). Mean ± s.e.m. number of oocyst was greater in the <it>An. gambiae </it>S form (1.72 ± 0.26) than in the <it>An. gambiae </it>M form (0.64 ± 0.04, p < 0.0001) and in the <it>An. arabiensis </it>group (0.58 ± 0.04, vs. S group, p < 0.0001). Sporozoite rate was also higher in the molecular form S (83.52%) than in form M (50.98%, Fisher's exact test p < 0.001) and <it>Anopheles arabiensis </it>50.85%, Fisher's exact test vs. S group p < 0.001).</p> <p>Conclusion</p> <p>Infected in the same experimental conditions, the molecular form S of <it>An. gambiae </it>is more susceptible to infection by <it>P. falciparum </it>than the molecular form M of <it>An</it>. <it>gambiae </it>and <it>An. arabiensis</it>.</p