Preliminary Screening of Entomopathogenic Fungi and Semiochemical Compatibility for a Potential Auto-Inoculation Strategy Against Frankliniella occidentalis

Abstract

Frankliniella occidentalis, an important crop pest worldwide, is mainly controlled by chemical pesticides, triggering resistance in thrips populations. Among the biological control methods evaluated in recent years, entomopathogenic fungi (EPF) appear to be a promising solution. A self-inoculation method could be an alternative that would increase specificity and reduce application costs. This requires efficient compatible semiochemicals and available EPF. The present study therefore consists of a preliminary screening of these components and their compatibility. Fungal strains were isolated from thrips cadavers with fungal infection symptoms in thrips populations reared in insect rearing cages. Out of twenty-three isolated fungal strains, one strain (Bb1) of Akanthomyces lecanii showed some efficacy for F. occidentalis biocontrol. Other strains potentially pathogenic to humans were not considered. The pathogenicity of the Bb1 strain and nine other EPF strains from our collection was assessed using an exploratory method in which the fungal treatments were applied to F. occidentalis eggs laid on bean pods. The reduction in the number of surviving individuals in the emerging population was evaluated after 8 days. The Bb1 strain caused a statistically significant mortality of 75%. In addition to that, the ten EPF strains were exposed to seven semiochemicals at concentrations of 1% and 10%. All semiochemicals showed an inhibitory effect. Moreover, geraniol, nerol and linalool at 10% were specifically deleterious, with 41%, 71% and 82% fungal growth inhibition, respectively. However, the inhibitory effect of semiochemicals depends on the strains tested. Thus, the radial growth of strain Bb1 is particularly little affected by verbenone, neryl (S)-2-methylbutanoate, methyl isonicotinate, and p-anisaldehyde. This work yielded a fungal strain of interest and the selection of potentially compatible semiochemicals attractive to F. occidentalis.