Spécificité des champignons pathogènes imparfaits [Hyphomycètes] pour les larves de coléoptères [Scarabaeidae etChrysomelidae]

Résumé L'étude de la spécificité des Hyphomycètes pathogènes de larves de Coléoptères a été effectuée avec diverses souches deBeauveria bassiana (Bals.) Vuill. B. tenella (Delacr.) Siem. Metarrhizium anisopliae (Metsch.) Sor. etNomuraea rileyi (Farl.) Sams. par contamination tégumentaire deCetonia aurata L.,Oryctes rhinoceros L.,Melolontha melolontha L. etLeptinotarsa decemlineata Say. Les essais ont été complétés par une contamination intrahémocoelienne dans le cas particulier des larves de Scarabeides. L'adaptation des pathotypes à leur h?te d'origine est confirmée chez les larves de Scarabeides et démontrée également après injection chezC. aurata etO. rhinoceros. Par contre, les larves de doryphore se révèlent sensibles à de nombreuses espèces et souches de champignons. Les résultats sont discutés par rapport aux travaux sur les relations h?teparasite en Phytopathologie et en Pathologie des Invertébrés.

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Summary Some strains ofBeauveria bassiana, B. tenella, Metarrhizium anisopliae andNomuraea rileyi were tested for specificity toCetonia aurata, Oryctes rhinoceros, Melolontha melolontha andLeptinotarsa decemlineata larvae. The contaminations were carried out by surface spray on larvae or by injection in the haemolymph with titrated spores suspensions. The experiments were conducted in blocks, each sequence of biossays was repeated 4 times. The results obtained were statistically interpreted after transformation of the mortality rates into angular values, which allowed the two-way analysis of variance and the comparison of the means by theDuncan & Staude's test. In the case of larvae ofL. decemlineata we have considered the time-mortality curves. By spraying it has been shown thatC. aurata, O. rhinoceros orM. melolontha larvae were susceptible only to the fungus strain isolated from insects of the same species. In the same conditions all twenty isolates were active on larvae ofL. decemlineata, but at a different degree. The host specialization of entomogenous Hyphomycetes strains cannot be considered as alone taxonomic criterion. According to epidemic works in plant infection it was appeared that host resistance of larvae ofScarabaeidae was vertical and that Colorado beetle larvae showed a horizontal susceptibility. After injection in the haemolymph ofC. aurata orO. rhinoceros larvae, the cryptogamic pathotypes were active only on their original host. The role of the defense reaction was discussed. Such investigations provided informations about the different modalities of the specificity of Hyphomycetes on insects.

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Avec la collaboration technique deP. H. Robert.