Potential shortfalls of using entomopathogenic fungi for boosting the sterile insect technique to control the oriental fruit fly, Bactrocera dorsalis

Abstract

Entomovectoring relies on the dissemination of biocides by insects to control plant pests and diseases. Current research aims at coupling entomovectoring with the Sterile Insect Technique (SIT). Such boosted-SIT is a promising technique to control the Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera, Tephritidae), an invasive pest that dooms African and Asian fruit-producers and is invading Europe. Here, we investigated empirically the potential of boosting the SIT using spores of the entomopathogenic fungus, Metarhizium anisopliae. Laboratory bioassay confirmed the transmission potential of the fungus from inoculated males to males and females, with subsequent reductions in survival and fecundity. Inoculation, like sterility, nonetheless reduced male mating success. Semi-field tests (i.e., large outdoor cages) revealed greater costs of fungal inoculation on male competitivity than observed in the laboratory. Combined with effects of inoculation on male survival, these costs led to a lower reduction in female reproduction in the presence of inoculated sterile males compared to plain sterile males. As tested here, boosting the SIT with M. anisoplae spores to control B. dorsalis could reduce its efficacy. The encouraging transmission patterns, however, suggest that technical improvements may render the boosted-SIT effective in some, if not all, ecological contexts.