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Accueil du site → Doctorat → Canada → Fièvre comportementale des acridiens (Orthoptera acrididoidae) Rôle de la thermorégulation dans la défense immunitairecontre les mycoses induites par les champignons entomopathogènes (Hyphomycètes)

Université Laval (2002)

Fièvre comportementale des acridiens (Orthoptera acrididoidae) Rôle de la thermorégulation dans la défense immunitairecontre les mycoses induites par les champignons entomopathogènes (Hyphomycètes)

Ouedraogo, Robert Maneguedo

Titre : Fièvre comportementale des acridiens (Orthoptera acrididoidae) Rôle de la thermorégulation dans la défense immunitairecontre les mycoses induites par les champignons entomopathogènes (Hyphomycètes)

Auteur : Ouedraogo, Robert Maneguedo

Université de soutenance : Université Laval

Grade : Doctor of Philosophy (Ph.D.) 2002

Résumé
Fungi are among the most important pathogens of grasshoppers and locusts, and present great potential for development as biological control agents. They are safer than the conventional chemical pesticides and may offer an environmentally sound method for insect pest management. However, behavioural fever mediated by thermoregulation in infected individuals, may restrict the use of those pathogens because fever is detrimental to pathogenesis. We assessed the occurrence of behavioural fever in seven acridid species from different ecological habitats, using three entomopathogenic fungi : ’ Beauveria bassiana, Metarhizium anisopliae’ var ’acridum’ and ’Verticillium lecanii’. Fever occurred in species from both temperate and tropical climates. However, species differed in their response to pathogens. One species, ’M.  femurrubrum’ did not develop a fever towards any of the pathogens tested. All pathogens were found to induce fever in at least some species. We used the association between ’Locusta migratoria’ and ’M. anisopliae’ to further study the implication of such behaviour on both the host and the pathogen. The analysis of the behavioural response of ’L. migratoria’ infected with the fungus revealed that the locust changed its thermoregulatory behaviour pattern, confirming its preference for higher temperatures. The frequency of food consumption however, was not altered. Variations of thermoregulation regimes affected insect mortality : mortality rates decreased with increasing duration of thermoregulation, and vice versa. Also, a delayed onset of thermoregulation increased mortality rates. Thermoregulation did not eliminate infection as its interruption was followed by resumption of mycosis. A study of hemocyte and blastospore kinetics gave new insights into the influence of thermoregulation on mycosis. In locusts allowed to thermoregulate, hemocyte concentrations were similar to those of control individuals. In contrast, in the absence of thermoregulation, hemocyte concentrations decreased dramatically, along with a heavy colonization of hemolymph by blastospores. Supporting these findings, the phagocytic activity was hampered in locusts that were not allowed to thermoregulate. In insects allowed to thermoregulate, our results suggest an enhanced phagocytic activity. The mechanisms involved are not known. We demonstrated that infection was followed by the synthesis of new hemolymph proteins. This is the first evidence for changes in the composition of protein in acridid hemolymph induced by infection with a fungus. Our results also showed a differential protein expression between thermoregulating and non-thermoregulating locusts. Whether and how these proteins account for the increased survival is not known. Thermoregulation plays an important role in host-pathogeninteractions. Its impact on the fungus may be direct through fungal growth inhibition by elevated temperatures or indirect through an enhanced immune defence. One consequence of such an influence is the enhanced survival of infected insects. The ultimate impact on the fungal potential to control grasshoppers and locusts needs further investigation.

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Page publiée le 12 février 2004, mise à jour le 15 septembre 2019