The Inevitable Fate of Tetranychus urticae on Tomato Plants Treated with Entomopathogenic Fungi and Spinosad

<i>Tetranychus urticae</i> (Acari: Tetranychidae) is a pervasive and damaging mite pest of tomato crops, leading to important economic losses globally. This study evaluated the acaricidal efficacy of spinosad, alone and in combination with <i>Beauveria bassiana</i> (<i>Bb</i>) WG-21 and <i>Metarhizium robertsii</i> (<i>Mr</i>) WG-04, in the laboratory (application to tomato leaf discs) and greenhouse (application to tomato plants), considering mortality and establishment, respectively. The combination treatments of <i>Bb</i> WG-21 or <i>Mr</i> WG-04 with spinosad achieved 100% mortality of <i>T. urticae</i> nymphs within 2 days on leaf discs, while individual applications of each control agent resulted in lower mortalities, ranging between 62.91 and 86.25% after 3 days. The paired treatment of <i>Mr</i> WG-04 + spinosad killed all exposed adults within 5 d, while that of <i>Bb</i> WG-21 + spinosad achieved the same results after 7 d. However, spinosad, <i>Mr</i> WG-04, and <i>Bb</i> WG-21 alone killed ≥77.08% of adults after 7 d. In the greenhouse, the combination treatment of WG-04 + spinosad deterred the presence of <i>T. urticae</i> (adults, immatures, and eggs) on either surface of the tomato leaves, while <i>Bb</i> WG-21 + spinosad suppressed the populations only on the adaxial surface. These findings indicate that combined treatments of the tested EPF + spinosad, especially <i>Mr</i> WG-04, on tomato plants under greenhouse conditions can provide substantially enhanced control of <i>T. urticae</i> life stages compared to each treatment applied alone.