Host-associated bioprospecting from Opisina arenosella: a Beauveria bassiana isolate against red palm weevil.

Host-associated bioprospecting of naturally infected insects provides a valuable approach for recovering indigenous entomopathogenic microorganisms adapted to local environments. In this exploratory study, seven microbial isolates (Four fungal and three bacterial) were recovered from naturally infected Opisina arenosella exhibiting signs of mycosis. Their pathogenicity was evaluated under laboratory conditions against larvae of the red palm weevil (RPW, Rhynchophorus ferrugineus). Among the recovered isolates, a single fungal isolate was identified as Beauveria bassiana (Zeb-01) and showed greater virulence compared with the other isolates obtained in this study. Morphological characterization using light and scanning electron microscopy, combined with molecular identification based on ITS and EF1-α sequencing, confirmed the identity of Zeb-01 and described its hyphal and conidial features. In laboratory bioassays, Zeb-01 caused dose- and time-dependent mortality, reaching 85% larval and 86% adult mortality at 1.0 × 10¹⁰ conidia/mL within 10 days. At the lowest tested concentration (1.0 × 10⁶ conidia/mL), mortality rates of 35% and 50% were recorded for larvae and adults, respectively. When evaluated under the same experimental conditions alongside a commercial B. bassiana formulation, Zeb-01 exhibited lower LC₅₀ and LT₅₀ values. These results document the isolation, identification, and laboratory evaluation of a single native B. bassiana isolate recovered from O. arenosella, and demonstrate its entomopathogenic activity against RPW, indicating its potential relevance for integrated pest management programs (IPM).