Target and non-target impact of oil-based Beauveria bassiana formulation in controlling forest insect pests

Pristiphora abietina (Hym.: Tenthredinidae) and Thaumetopoea wilkinsoni (Lep.: Notodontidae) are among the most detrimental forest pests in Türkiye. In this study, a prototype oil-based formulation named Pa4-OD was developed to control both P. abietina and T. wilkinsoni . Under laboratory conditions, the mortality rates for P. abietina and T. wilkinsoni larvae were 95.5% and 98.6%, respectively, 14 days after treatment with a spore concentration of 1 × 10 8 spores/mL. The median lethal concentrations (LC 50 ) of Pa4-OD were determined to be 2.6 × 10 3 for P. abietina and 7.9 × 10 6 spores/mL for T. wilkinsoni . The formulation was applied against T. wilkinsoni in the field experiment, resulting in 89.9% mortality at 1 × 10 9 blastospores/mL after three weeks (p < 0.05). Furthermore, the mycoinsecticide exhibited minimal adverse effects on Calosoma sycophanta L. (a predator of T. wilkinsoni ), Rhizophagus grandis Gyllenhal (a predator of Dendroctonus micans Kugelann is one of the most important pests of spruce forestry) and Thanasimus formicarius L. (another predator for forestry pests). The mortality rate of Apis mellifera caucasica Pollmann adults resulted in 76.6%, with mycosis observed in only 21% of individuals after ten days of exposure to a spore concentration of 1 × 10 9 spores/mL. However, few side effects were observed at other doses (1 × 10 5 to 1 × 10 8 spores/mL). This study demonstrated that mycoinsecticide development from the local entomopathogenic fungus B. bassiana could potentially be utilized to control P. abietina and T. wilkinsoni in Türkiye. Pa4-OD provides effective pest control while minimizing harm to beneficial insects, reducing reliance on synthetic insecticides, and supporting environmentally sustainable forest management.