Compatibility and Synergistic Effects of Plant Biostimulants and Commercial Entomopathogenic Fungi for Diaphorina citri Pathogenicity

The Asian citrus psyllid (ACP), Diaphorina citri, is the primary vector of Huanglongbing, a devastating disease threatening global citrus production. While chemical insecticides dominate control strategies, environmental and resistance concerns necessitate sustainable alternatives like Integrated Pest Management. This study evaluated the efficacy of commercial entomopathogenic fungi (EPF) formulations (Beauveria bassiana, Metarhizium anisopliae, and Cordyceps javanica) alone or combined with plant biostimulants (PBS; silicon dioxide and chitosan) across six greenhouse bioassays. Under hot, dry stress conditions (34 °C, 35% RH), stand-alone and PBS-paired EPF applications failed to induce significant D. citri mortality, highlighting environmental microclimate limitations. Conversely, under optimal controlled conditions (26 °C, 67% RH), biological treatments significantly increased mortality compared to untreated controls. Notably, the addition of PBS containing silicon dioxide and D-glucosamine into the spray did not exhibit antagonistic effects on fungal performance; instead, it significantly enhanced ACP mortality and survival reduction in several trials. While synthetic chemical control provided the fastest and highest initial mortality, these results demonstrate that tank-mixing commercial EPFs with silicon-dioxide-chitosan biostimulants is a compatible, viable, and highly promising strategy to optimize sustainable vector management under permissive environmental conditions.