Occurrence and persistence of entomopathogenic fungi in soil following experimental application of Beauveria pseudobassiana in oak forests infested by Corythucha arcuata

The invasive oak lace bug Corythucha arcuata Say (Heteroptera: Tingidae) continues to spread across European oak forests, while effective and environmentally acceptable control options remain limited. Following the identification of a local strain of the entomopathogenic fungus Beauveria pseudobassiana associated with overwintering populations of this pest, this study aimed to assess its occurrence and persistence in soil after experimental application under field conditions. Natural levels of entomopathogenic fungi (EPF) were investigated in soil from a pedunculate oak forest in Croatia infested for a long time by C. arcuata , and the persistence of an experimentally applied B. pseudobassiana inoculum was evaluated. Moss on tree bases, serving as the overwintering niche of the pest, was treated with mass-produced fungal conidia. Soil was sampled once before treatment and on five post-treatment occasions between May 2023 and April 2024. EPF were isolated using selective media and identified by morphological and molecular methods. Six entomopathogenic species and one genus-level taxon were identified, with B. pseudobassiana being the most frequently identified entomopathogenic taxon. Following treatment, colony-forming units (CFU) of B. pseudobassiana increased markedly around treated trees relative to controls and subsequently declined over time. After one year, CFU levels did not differ from pre-treatment values, suggesting limited persistence under the studied conditions, with no detectable long-term increase in CFU levels. These findings provide insight into the persistence of B. pseudobassiana in soil and inform its potential use in biological control strategies against C. arcuata.