Infection of the Red Palm Weevil (Rhynchophorus ferrugineus) by the entomopathogenic fungus Beauveria bassiana: A SEM study

The Red Palm Weevil (Rhynchophorus ferrugineus) is a devastating pest of palms in the Mediterranean, Middle East, and Eastern countries. No effective control measures are available. R. ferrugineus has been found naturally infected by the entomopathogenic fungus Beauveria bassiana, but its infection process in this host is unknown. We have studied the infection of R. ferrugineus larvae and adults by B. bassiana using dry conidia and conidia suspensions using scanning electron microscopy (SEM). In early stages, SEM revealed acquisition of B. bassiana conidia by cuticle ornamentation in legs, antennae, and elytra of R. ferrugineus adults. Subsequently, conidia germinated and frequent episodes of hyphal/conidial fusion were found. Appressoria, signs of adhesion and cuticle degradation led to penetration (even direct) and colonization of R. ferrugineus hosts by the fungus. B. bassiana conidiophores were found in a R. ferrugineus cuticle, which indicate the completion of the life cycle of the fungus in the insect host. SEM has proven that dry conidia of B. bassiana is an adequate inoculum for R. ferrugineus infection. SEM revealed that conidia of B. bassiana attached to the cuticle of R. ferrugineus can germinate and differentiate appressoria.