Biological control of the red palm weevil, Rhynchophorus ferrugineus olivier (coleoptera: curculionidae) using indigenous Beauveria bassiana (Bb-045) in coconut palms

Abstract Background India is the world’s leading producer of coconuts, with 2.08 million hectares under cultivation, yielding a total production of 22,167 million nuts annually. However, various biotic and abiotic constraints limit global palm yields. Among the biotic factors, the coconut red palm weevil, Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae) (RPW) poses a significant challenge in India. This pest attacks the crown regions, resulting in death of the palm. Most of the developmental stages of this weevil are concealed within the palm trunk, which not only hinders early detection but also facilitates rapid reproduction. The indiscriminate use of chemical insecticides to control these pests has caused significant environmental and regulatory concerns, highlighting the need for ecologically safe and environmentally friendly alternatives. In this context, a native entomopathogenic fungus, Beauveria bassiana (Bb-045) (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae), has been isolated and its efficacy was evaluated against the third instar larvae of R. ferrugineus . Results Larval susceptibility of the RPW varied significantly with the treatment dose and exposure period. The indigenous isolate, Bb-045, demonstrated high virulence against the 3 rd instar larvae, causing up to 98% mortality at 14 days after treatment (DAT) at the highest spore concentration tested (1 × 10 8 conidia/ml). The LC 50 value was determined to be 4.83 × 10 4 conidia/ml at 14 DAT, while the LT 50 value was calculated as 8.51 days at 1 × 10 8 conidia / ml . Furthermore, an invert emulsion formulation of Bb-045 was tested through palm trunk inoculation studies, achieving over 90% mortality of red palm weevil larvae within 14 days at a spore concentration of 5.2 × 10 8 conidia/ml. The invert emulsion formulation (Bb-045) exhibited high RPW mortality, suggesting its potential as a bio-pesticide in RPW management programs. Conclusions Based on virulence, and efficacy, the Bb-045 strain showed significant potential as a biocontrol agent for managing Rhynchophorus ferrugineus in coconut palms, particularly in humid tropical ecosystems. The present study identified an effective native strain and demonstrated its field efficacy. Thus, the invert emulsion formulation of Bb-045 could be integrated into red palm weevil management programs in coconut cultivation as an efficient biological control agent.