Résumé:
During the past century, agriculture went through significant ameliorations which resulted in a general yield increase, to which chemical pesticides greatly contributed. However, their negative environmental impacts had been early documented, and it is now established that these chemicals cannot represent a solution for a sustainable agriculture. Chemical residues in food, micro-pollutants in soils and water, selection of resistance of pathogens and pests are all harsh consequences impacting human health and biodiversity. Entomopathogenic fungi represent an interesting alternative to chemicals for crop protection against phytophagous insects and participate to a sustainable phytosanitary control. In this work, new fungal strains were isolated from soils of organic apple tree orchards and natural spaces, in the Canton of Geneva, with a baiting method using larvae of Galleria mellonella. All 71 collected isolates were genetically identified by PCR amplifications and sequencing of the rDNA ITS sequence. Out of these 71 isolates, 40 isolates belonged to entomopathogenic species. The baiting method with Galleria mellonella proved to be very efficient and showed that natural and untreated environments were generally richer in species and isolates. Interesting fungal strains belonging to the genera Beauveria, Metarhizium and Paecilomyces were isolated. Twelve of the most interesting isolates were then tested on the aphid pest Myzus Persicae. In a separate experiment, seven isolates of Metarhizium sp. were tested against the aphid Acyrthosiphon pisum. Experiments on the two aphids showed a strong virulence and entomotoxicity of some of the isolates. A mortality between 86.67% and 100% was recorded on Myzus persicae with 4 strains (2 Beauveria bassiana, 1 Metarhizium sp., 1 Paecilomyces sp.). The filtrates with spores were the most efficient against Myzus persicae. The filtrates without spores of the seven Metharizium sp. strains tested on Acyrthosiphon pisum caused a mortality of 100% after 7 days (control: mortality of 5% after 7 days) highlighting a very interesting potential of entomotoxicity of these fungi.
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