Effect of Endophytic Fungi on <i>Thrips tabaci</i> Development and Population Dynamics

ABSTRACT Endophytic fungi are promising biocontrol agents because they colonise healthy plant tissues asymptomatically while inducing systemic resistance that negatively affects herbivorous insects. We investigated whether treatments with the endophytes Trichoderma harzianum and Beauveria bassiana in two onion cultivars ( Allium cepa L.; Sturon and Red Baron) induce plant responses that alter Thrips tabaci behaviour and population development. Under controlled conditions, seeds were treated with conidial suspensions and plants subsequently received foliar applications; plants were then exposed to T. tabaci for 72 h, 4 weeks, or 8 weeks in no‐choice assays. Both endophytes reduced thrips host‐plant preference: at 72 h post‐exposure, inoculated plants had 2.01–2.89‐fold fewer feeding punctures and 2.78–3.93‐fold fewer eggs than controls. Over longer durations, endophyte treatments also suppressed thrips population growth: after 4 and 8 weeks, significantly more thrips were collected from control plants than from endophyte‐colonised plants. Thrips populations did not differ between the two onion cultivars across treatments and time points. We discuss targeted inoculation of onions with specific endophytic fungal strains as a strategy for sustainable thrips management and its prospects for field implementation.