| dc.contributor.author | Mahot, H.C. |
| dc.date.accessioned | 2022-10-26T10:34:58Z |
| dc.date.available | 2022-10-26T10:34:58Z |
| dc.date.issued | 2019 |
| dc.identifier.citation | Mahot, H.C. (2019). Utilisation des champignons entomopathogenes et des pieges a pheromones dans la lutte contre Sahlbergella singularis Haglund, 1895 (Hemiptera : Miridae), bio-agresseur du cacaoyer au Cameroun. Yaounde, Cameroon: University of Yaounde, (25p.). |
| dc.identifier.uri | https://hdl.handle.net/20.500.12478/7909 |
| dc.description.abstract | Le cacao fait partie des produits qui font vivre plus de 3 millions de personnes au Cameroun. Malgré l’objectif gouvernemental qui vise 600.000 tonnes de fèves de cacao par an à l’horizon 2020, la production cacaoyère reste faible en raison de la pression des maladies et des ravageurs. Dans l’entomofaune nuisible associée au cacaoyer, les hémiptères et précisément les Miridae constituent le groupe d’insectes le plus préjudiciable. De nos jours, la recherche des alternatives à la lutte chimique contre les mirides est un challenge. Les champignons Beauveria bassiana et Metarhizium anisopliae et les pièges à phéromones suscitent de plus en plus d’espoirs et constituent des issues importantes en lutte biologique et en lutte semiochimique. Ce travail a évalué le pouvoir insecticide des isolats de B. bassiana et de M. anisopliae vis-à-vis de Sahlbergella singularis dans le but de mettre au point et sélectionner des formulations de biopesticides. Il a essentiellement évalué l’attractivité des pièges de differentes couleurs, appâtés aux phéromones, vis-à-vis de S. singularis et déterminé l’impact de ces pièges à phéromones sur sa densité et ses dégâts en milieu réel. Les isolats de Beauveria bassiana et Metarhizium anisopliae testés avec la méthode par immersion et celle par ingestion ont montré un potentiel insecticide intéressant au laboratoire contre les larves de S. singularis. Ils ont causé des mortalités pouvant atteindre des taux de 100%. Les épreuves biologiques ont permis de retenir quatre des six isolats fongiques sur la base des concentrations létales 50 (CL50) ; des temps létaux 50 (TL50) et 90 (TL90) et deux isolats BIITAC6.2.2 et MIITAC11.3.4, après le test de transmission horizontale. Les paramètres croissance végétative, sporulation, germination et biomasse fongiques ont démontré que le glycérol, l’huile de soja, l’huile de palme raffinée et l’huile de coton ont une bonne compatibilité avec les souches de champignons selectionnées. Ces mêmes paramètres ont servi à sélectionner la formulation de type Emulsion Inverse (EI), qui a mieux conservé la viabilité des spores de B. bassiana et de M. anisopliae pendant 18 semaines d’une part et, d’autre part, la température de 25oC qui est la plus favorable à la conservation des formulations. Les toxicités des conidies de B. bassiana et de M. anisopliae formulées en laboratoire avec l’huile de soja et avec l’huile de palme raffinée ont été avérées avec des taux moyens de mortalité des mirides compris entre 76% et 84%. L’espèce B. bassiana a montré un effect insecticide relativement plus élevé que M. anisopliae; la pathogénicité de ses conidies formulées a indiqué, en cacaoyère, une efficacité certaine. Ainsi, l’insecticide de B. bassiana formulé à base d’huile de soja a significativement réduit les populations de mirides comparé au témoin. Cette réduction a atteint un taux de 100% au bout du trente-sixième jour d’essai. La viabilité des conidies de B. bassiana sur les feuilles de cacaoyer se maintient et ne se perd considérablement qu’après un mois post-application, soit une perte de 72% au bout de deux mois. La persistance de l’activité insecticide de B. bassiana sur les cabosses de cacaoyer, au bout de deux mois post-application, a été induite malgré les conditions abiotiques. Le type de formulation influence l’efficacité du champignon comme agent de bio-contrôle, sa facilité d'application et sa durée de conservation. Ces atouts, à prendre en compte dans la mise au point d’une formulation fongique, sont importants dans une stratégie phytosanitaire de contrôle de populations des insectes ravageurs. Parallèlement à l’investigation d’une stratégie de lutte biologique par ces champignons, l’optimisation de l’utilisation des pièges par l’intégration du paramètre « couleurs » a été menée à Ayos et à Konye. D'après les réactions comportementales des mirides, toutes les couleurs de pièges utilisées ont été attractives avec une préférence pour le piège vert. La préférence pour les pièges verts s’est expliquée par le mimétisme de la couleur du matériel végétal. En tout, 4191 mirides ont été échantillonnés dans les deux localités d’étude soit 3826 dans les parcelles avec pièges et 368 dans les parcelles sans pièges (témoin). Les profils des courbes de pluviométrie, de température et d’humidité relative n’ont pas toujours coïncidé avec celui de la dynamique de population de S. singularis qui n’a pas trouvé une explication directe par ces facteurs abiotiques. Ces derniers semblent influencer plutôt l’état physiologique du cacaoyer qui, à son tour, détermine la dynamique spatio-temporelle de S. singularis dans les plantations cacaoyères. La prévalence des dégâts sur la plante hôte (cabosses) dus à S. singularis a été moins élevée dans les parcelles avec pièges (essai) comparées aux parcelles témoins. Dans la localité d’Ayos, le taux moyen de cabosses affectées a été de 1,7 % dans les parcelles essais contre 3,6% dans les témoins tandis qu’à Konye, il a été de 1,3 % contre 5,5% respectivement. La sévérité des dégâts de S. singularis chez la plante hôte (cabosses) dans les parcelles témoins a été plus importante que celle dans les parcelles essais, soit 1,06% et 0,53% à Ayos contre 1,63% et 0,42% à Konye respectivement. Les niveaux élevés de prévalence des dégâts et de sévérité dans les parcelles témoins comparées aux parcelles traitées suggèrent que l’utilisation du piégeage réduit les dommages causés par les mirides sur les cabosses bien que le niveau de captures de S. singularis mâles dans les pièges appâtés, n'a pas montré une réduction considérable des dégâts sur les cabosses de cacaoyer. Cocoa is one of the products that provide important incomes for more than 3 million people in Cameroon. Despite the government's target yield of 600,000 tons by 2020, cocoa production remains low due to diseases and pests. In the insect wildlife pest associated with cocoa trees, Hemiptera specially Miridae are the most damaging group of insects. Research for alternatives to chemical control of mirids has today become a challenge. The use of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae and pheromone traps are increasingly of interest and are important output in biological and semiochemical control. This work has assessed the insecticidal potential of fungal isolates of B. bassiana and M. anisopliae against Sahlbergella singularis to develop and select biopesticide formulations. It has specially evaluated the attractiveness of the baited colored traps by S. singularis and determined the impact of these pheromone traps on their density and their damages in natural environments. Beauveria bassiana and Metarhizium anisopliae isolates tested through immersion and ingestion methods showed interesting insecticidal potential in the laboratory against S. singularis larvae. They have caused mirid death that could reach the average rates of 100%. Bioassays tests and the evaluation of lethal concentrations 50 (LC50) and lethal times 50 (TL50) and 90 (TL90) allowed the screening of four fungal isolates between the six tested. However, only two strains, namely BIITAC6.2.2 and MIITAC11.3.4 were transmitted horizontally. Fungal vegetative growth, sporulation, germination and biomass have shown that glycerol, soybean oil, refined palm oil and cottonseed oil have good compatibility with fungi. These same parameters also helped to select the Reverse Emulsion (EI) formulation, which better preserved the viability of B. bassiana and M. anisopliae spores for 18 weeks in one hand and in the other hand to choose the temperature of 25ºC, which is the most favourable for the conservation of the formulations. Toxicity of B. bassiana and M. anisopliae conidia formulated in the laboratory with soybean oil and refined palm oil have been proven with the mirid mortality average rates ranged from 76% to 84%. B. bassiana was relatively more toxic to mirids than M. anisopliae; the pathogenicity of its formulated conidia has indicated an incontestable efficacy in cocoa field. The mycoinsecticide of B. bassiana, formulated with soybean oil, significantly reduced mirid populations compared to the control. This reduction reached an average rate of 100% after thirty-six days of product application. The viability of B. bassiana conidia on cocoa leaves is maintained and it is significantly lost only a month after application; either a losses of 72% after two months. The persistence of insecticidal activity of B. bassiana on cocoa pods two months after application was induced despite abiotic conditions. The type of formulation affects the efficacy of the fungus as a bio-control agent, its safe application and its shelf life. These assets are to be considered in the development of fungal formulation as it is essential in a phytosanitary strategy of insect pests population control. Beside the investigation of a biological control strategy by B. bassiana and M. anisopliae, the optimization of trap using by color integration was also carried out in the localities of Ayos and Konye. According to the behavioral reactions of the mirids, all trap colours were attractive with preference for the green trap. The preference for green traps was explained by the imitation of the colour of the plant material. A total of 4191 mirids were sampled in the two study sites, 3826 in the plots with traps (treated) and 368 in the plots without traps (control). The profiles of the rainfall, temperature and relative humidity curves did not always coincided with those of the S. singularis population’s dynamics which have not found a direct explanation in these abiotic factors variation. These abiotic factors seem to influence the physiological state of the cocoa tree, which could determine the spatio-temporal dynamics of S. singularis in cocoa plantations. The prevalence of host plant damage (pods) caused by S. singularis was lower in trap plots (treated) compared to control plots. In Ayos, the average rate of affected pods was 1.7% in treated plots compared to 3.6% in controls, while in Konye, it was 1.3% compared to 5.5% respectively. The severity of damage of S. singularis in the pods in control plots was greater than the one in treated plots, i.e. 1.06% and 0.53% in Ayos against 1.63% and 0.42% in Konye respectively. The high levels of damage prevalence and severity in the control plots compared to treated plots suggest that the use of trapping method reduce the damage caused by mirids on pods despite the fact that the level of catches of S. singularis male by pheromone traps did not shown a considerable reduction in damage of cocoa pods. |
| dc.language.iso | fr |
| dc.publisher | University of Yaounde |
| dc.subject | Beauveria Bassiana |
| dc.subject | Metarhizium Anisopliae |
| dc.subject | Biological Control |
| dc.subject | Pathogenicity |
| dc.subject | Cocoa Pods |
| dc.subject | Diseases |
| dc.subject | Pests |
| dc.subject | Insecticides |
| dc.subject | Fungi |
| dc.subject | Soybeans |
| dc.subject | Preservation |
| dc.title | Utilisation des champignons entomopathogenes et des pieges a pheromones dans la lutte contre Sahlbergella singularis Haglund, 1895 (Hemiptera : Miridae), bio-agresseur du cacaoyer au Cameroun |
| dc.type | Thesis |
| cg.contributor.affiliation | University of Yaoundé |
| cg.contributor.affiliation | International Institute of Tropical Agriculture |
| cg.coverage.region | Africa |
| cg.coverage.region | Central Africa |
| cg.coverage.country | Cameroon |
| cg.coverage.hub | Central Africa Hub |
| cg.identifier.bibtexciteid | MAHOT:2019 |
| cg.authorship.types | CGIAR and developing country institute |
| cg.iitasubject | Cocoa |
| cg.iitasubject | Disease Control |
| cg.iitasubject | Food Security |
| cg.iitasubject | Handling, Transport, Storage and Protection of Agricultural Products |
| cg.iitasubject | Pests of Plants |
| cg.iitasubject | Plant Breeding |
| cg.iitasubject | Plant Diseases |
| cg.iitasubject | Plant Production |
| cg.iitasubject | Soybean |
| cg.notes | IITA supervisor: Dr. Hanna, R., Fotso Kuate, A. |
| cg.publicationplace | Yaounde, Cameroon |
| cg.accessibilitystatus | Limited Access |
| cg.reviewstatus | Peer Review |
| cg.usagerightslicense | Copyrighted; all rights reserved |
| cg.targetaudience | Scientists |
| cg.futureupdate.required | No |
| cg.contributor.acknowledgements | This work would not have seen its completion without the opportunities offered by a certain number of laboratories and projects. I am thinking in particular of the Laboratories of Entomology and Pathology of the International Institute of Tropical Agriculture (IITA), Biological Control and
Applied Microbiology from the Institute of Agricultural Research for Development (IRAD), finally of Parasitology and Ecology of the University of Yaoundé I. The project for the increase of productivity of small producers and the reduction of deforestation and degradation of ecosystems, called Cocoa-Eco, and the Program of Green Innovation Centers for the Agro-food sector, called Procisa, have by the financing granted to me been of an unwavering support. The completion of this work was only possible thanks to the contribution of the people to whom I must express my deep gratitude and gratitude.
So I extend my sincere thanks to:
- to Doctor HANNA Rachid, Director of Research at IITA, for having participated in the conception and supervision of this work. That its financial and technical support, its encouragement and advice throughout my internship at IITA find here the expression of my sincere and distinguished thanks;
- to Professor BILONG BILONG Charles Félix, Head of the Parasitology Laboratory and of Ecology and Head of the Department of Animal Biology and Physiology at the Faculty of Sciences of the University of Yaoundé I, for having accepted, despite his many concerns, to supervise this work. I would like to express to him all my gratitude and my deep respect for the attention he paid to the realization of this thesis and for his constructive criticism;
- to Doctors BEGOUDE BOYOGUENO Aimé-Didier, Director of Research at IRAD, FOTSO KUATE Apollin, Visiting Scientist at IITA, MAHOB Raymond and YEDE, both Teacher-Researchers at the Department of Animal Biology and Physiology of the Faculty of sciences of the University of Yaoundé I, for agreeing to follow this work closely. Their technical assistance, their availability as well as their many advices and encouragements were instrumental in the completion of this thesis. I sincerely thank them for everything;
- to Doctor BAGNY BEILHE Leïla, researcher at the Center for International Cooperation in Agronomic Research for Development (CIRAD), for his enthusiasm, his availability and especially his advice during the initial phase of this work;
- to all teachers of the Department of Animal Biology and Physiology of the Faculty of Sciences of the University of Yaoundé I, for teaching, advice and supervision that they gave me;
- to my Laboratory colleagues, Ladies MEJANE EKANE Carole, MEMBANG Gertrude and NGO NGAMBI Anne Flore; Messrs. TONYE III Stéphane Daves, NANGA Samuel and DONGMO Arnaud Michel, for their various contributions and/or their permanent criticisms;
- To Messrs. NYIAWUNG Richard, BIYAGA Stéphane, ANDOUBA Javis Etoh for their support in the collection of data in the field;
- to my family in the broad sense and in particular to my son MAHOT Ange Roland, my daughters
MAHOT Suzanne Rolande Florenda and NGO MOOH Suzanne Marlyse, for their love, their presence at my side and especially for their patience; my sisters MAHOT Marguerite and MAHOT Suzanne and my brothers SIMB Bertrand Flavien and MAHOT Marcellin for their attention, their multifaceted and unwavering support;
- to all staff of the Institute's Entomology and Pathology Laboratories Institute of Tropical Agriculture (IITA), Parasitology and Ecology of the University of Yaoundé I, finally Biological Control and Applied Microbiology of the Research Institute Agriculture for Development (IRAD);
- to all the teams of the Cocoa-Eco and Procisa projects for the technical support and the good atmosphere that has always reigned in the group. The many descents we made on the field have edified me on life in general and on teamwork;
I give thanks to Almighty and Merciful God for giving us good health, courage, will and patience to carry out this work. |
