Virulence of Beauveria bassiana Strains Isolated from Cadavers of Colorado Potato Beetle, Leptinotarsa decemlineata

SIMPLE SUMMARY: The Colorado potato beetle is a serious insect pest, attacking mainly potato. This pest causes severe yield loss all over the world and it is difficult to control by chemical pesticides because it quickly develops resistance to them. In our study we investigated the potential of the fungus Beauveria bassiana, a natural pathogen of insects, to kill adults of the Colorado potato beetle. The novelty of this study is that strains of the fungus were isolated from naturally infected adults of the pest which were collected in potato fields in the Czech Republic. A suspension of B. bassiana spores was applied to test beetles and their survival was observed under constant conditions. Obtained results revealed that some strains of the fungus were able to kill almost all treated beetles in 21 days and can be therefore recommended for the development of a new biopesticide. The results of this study can thus be applied in effective biological control of the most serious pest of potato. ABSTRACT: The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a serious, widely distributed pest of potato and other crops. This pest is able to defoliate the host plant and cause severe yield loss. Moreover, the pest quickly becomes resistant to many chemical pesticides. Therefore, the development of novel biopesticides targeting this pest is urgently needed. The purpose of this study was to obtain new strains of the entomopathogenic fungus Beauveria bassiana and assess their efficacy against L. decemlineata adults under laboratory conditions. Twelve strains were isolated from cadavers of Colorado potato beetles collected in potato fields in the Czech Republic. Test beetles were treated by suspensions of conidia at the concentration of 1 × 10(7) spores per milliliter and their survival was recorded daily for three weeks. The results of the bioassays revealed that all new native strains were pathogenic to L. decemlineata adults and caused mortality up to 100% at the end of the trial period with an LT(50) of about 7 days. These strains were more virulent than a reference strain GHA and some of them can be recommended for the development of a new mycoinsecticide against L. decemlineata. Our findings also highlight the importance of searching for perspective strains of entomopathogenic fungi among naturally infected hosts.