Screening of Highly Virulent Beauveria bassiana Strains Against Tuta absoluta Larvae and Evaluation of Their Endophytic Colonization-Mediated Suppression in Tomato Plants

To identify highly virulent <i>Beauveria bassiana</i> strains against <i>Tuta absoluta</i> and evaluate their biocontrol potential, four strains were phylogenetically characterized via ITS sequence analysis of rDNA and assessed for virulence against second-instar <i>T. absoluta</i> larvae. Foliar spray and root irrigation methods were used to establish <i>B. bassiana</i> endophytic colonization in tomato plants, with untreated plants serving as controls. A population life table was constructed to quantify the impact of colonized plants on larval development, fecundity, and key demographic parameters. Results showed variation in virulence among the four <i>B. bassiana</i> strains Bb1Bm, Bb2Bm, Bb1M, and BbC with Bb1Bm exhibiting the highest pathogenicity (85.00% corrected mortality at 1 × 10⁸ spores/mL). Maximum endophytic colonization in tomato leaves was observed 14 days post-inoculation with both foliar spray and root irrigation treatments. Life table analyses revealed that <i>T. absoluta</i> feeding on colonized plants exhibited significantly reduced survival rates, shorter adult lifespans, and lower female fecundity compared to controls. Key population parameters, including net reproductive rate (<i>R</i>₀), intrinsic rate of increase (<i>r</i>), and finite rate of increase (<i>λ</i>), were significantly reduced, while mean generation time (<i>T</i>) was significantly prolonged. These findings highlight the dual role of <i>B. bassiana</i> in <i>T. absoluta</i> management, demonstrating its potential as both a direct pathogen and an endophytic biocontrol agent capable of disrupting pest population dynamics.