Specific detection of strains of Beauveria brongniartii pathogen towards Hoplochelus marginalis

The strain Bt96 of the entomopathogenous fungus Beauveria brongniartii was introduced in La Réunion Island in order to control the populations of the white grub Hoplochelus marginalis, a new pest of sugar cane crops. Molecular analyses of 32 strains of B. brongniartii from various biological and geographical origins revealed the specificity of the host-pathogen relation between H. marginalis and B. brongniartii. A thorough characterization of different strains pathogen towards Hoplochelus allowed to develop a specific detection method of the strain Bt96. By studying the 28S rDNA, different group I introns were found with variable distribution among the 32 studied strains. All strains of B. brongniartii isolated from H. marginalis contain a specific group I intron which is absent in the strains isolated from other hosts. A nucleotide sequence was determined in this specific intron as primer for polymerase chain reaction (PCR), allowing specific amplification of strains isolated froin Hoplochelus. Moreover, the size of the amplified product is original in the strain Bt96 because all other studied strains possess an additional intron in this fragment. This detection method which is sensitive, fiable and specific allowed the ecological monitoring of this strain in experimentation fields. We present on one hand, the repartition within the island of this strain and of indigenous strains, and on an other hand, the results of a laboratory competition test conducted on Hoplochelus larvae. This last experimentation is currently performed in field. (Résumé d'auteur