Dual-strategy approach for Rhynchophorus ferrugineus control: Endophytic Beauveria bassiana and Bacillus thuringiensis topical application

In an innovative approach to biological pest management, the entomopathogenic efficacy of endophytically colonized Beauveria bassiana and topically applied Bacillus thuringiensis was evaluated against various larval instars (2nd, 4th, and 6th) of the red palm weevil (RPW), Rhynchophorus ferrugineus. Initially, date palm leaf petioles were inoculated with five distinct isolates of the fungus to ascertain their endophytic potential over two years. Subsequently, the most proficiently colonized fungal isolate was selected for subsequent experimentation. During individual entomopathogen applications, larval instars of RPW were presented with plant petioles and colonized with fungus at 30 days post-inoculation or immersed in bacterial inoculum. Ιn combined treatments, larvae were exposed to both entomopathogen-treated plant petioles concurrently. The tested bacterium was administered at three concentrations (30, 40, and 50 μg/ml). Larval mortalities were markedly lower in treatments involving individual entomopathogens, whereas integrated applications yielded higher mortalities. Treatments associated with heightened larval mortalities corresponded to diminished pupation, adult emergence, and egg eclosion rates. Furthermore, the simultaneous application of both entomopathogens bolstered larval mortalities of RPW both additively and synergistically, with concentration also playing an important role. Similarly, the developmental periods of various insect stages were substantially influenced by combined entomopathogen applications. The inherent prevalence of these pathogens and their ability to colonize crop plants internally for extended periods render them promising agents against cryptic-feeding insects like RPW. However, further evaluation of suitable entomopathogen strains and optimal doses under field conditions is imperative before formulating concrete recommendations for date palm growers.