Screening of semio-chemical molecules and entomopathogenic fungi for an auto-dissemination control strategy against Frankliniella occidentalis

Abstract: With the aim of creating an auto-inoculation trap of entomopathogenic fungi against Frankliniella occidentalis, three thysanopteran populations originated from field samples, were reared in microcosms in climatic chambers and genetically identified as belonging to the species F. occidentalis. Simultaneously, a fungal bioassay on the cadavers collected in the thrips rearing allowed the isolation of a strain (Bb1), further identified as Lecanicillium lecanii, a species of interest for this study. Subsequently, the entomopathogenicity of a local proprietary collection of 11 Beauveria and Metarhizium spp. strains was screened on an egg-laying sample of F. occidentalis. The Lecanicillium lecanii strain Bb1 caused the greatest population decrease at 75 %, and was the only one to be statistically significant from the negative control. In comparison, the Beauveria bassiana strain contained in the commercial product Naturalis-L® caused only 12 % mortality. In parallel, the fungistatic capacities of 7 attractive molecules of F. occidentalis (attraction pheromone and kairomones) were screened on the same fungal isolates at two different concentrations, namely 1 % and 10 %. All treatments showed a fungistatic action as they were statistically significant compared to the negative control. However, linalool, nerol and geraniol at a concentration of 10 % especially impacted the growth of the fungal isolates
and were statistically significant compared to the other treatments. This work therefore allowed the selection of thrips semiochemical molecules with a weak fungistatic effect against the fungal strains of interest for the control of F. occidentalis, as well as the isolation, identification, demonstration of the virulence potential and sensitivity of a fungal strain potentially useful for controlling this thrips species.