Synergistic Effects of Beauveria bassiana and Insecticides for Integrated Management of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

<i>Bactrocera dorsalis</i> (Hendel) (Diptera: Tephritidae) is a significant agricultural pest that causes substantial economic losses globally. While chemical insecticides are commonly used for its management, increasing resistance and environmental concerns underscore the need for alternative control strategies. This study evaluated the potential of integrating the entomopathogenic fungus <i>Beauveria bassiana</i> strain Bb-33 (Hypocreales: Clavicipitaceae) with reduced doses of chemical insecticides for sustainable <i>B. dorsalis</i> management. The compatibility of <i>B. bassiana</i> Bb-33 with six commonly used insecticides-spinosad, emamectin benzoate, avermectin, thiamethoxam, beta-cypermethrin, and imidacloprid-was assessed. Among them, emamectin benzoate exhibited the least inhibitory effects on spore germination, mycelial growth, and sporulation of <i>B. bassiana</i>. Laboratory bioassays demonstrated synergistic interactions between <i>B. bassiana</i> Bb-33 and emamectin benzoate, particularly when the ratio of emamectin benzoate to <i>B. bassiana</i> exceeded 4:1, as indicated by co-toxicity coefficients greater than 100. However, greenhouse trials revealed that the combined formulation had lower efficacy in reducing <i>B. dorsalis</i> adult populations and pupal emergence rates compared to emamectin benzoate alone, though it was more effective than <i>B. bassiana</i> Bb-33 applied independently. Importantly, this composite formula reduces pesticide usage, which highlights its potential to mitigate environmental impacts. This study underscores the promise of integrating <i>B. bassiana</i> Bb-33 with reduced doses of emamectin benzoate as a viable strategy for managing <i>B. dorsalis</i>. Despite its current limitations in greenhouse trials, further optimization of formulation stability and application methods could enhance its field performance, offering an effective and environmentally friendly alternative to conventional chemical control methods.