Evaluation the pathogenicity of two isolates of Beauveria bassiana Vuill (Bals.) on Spodoptera cilium Guenee larvae under laboratory and field conditions

Spodoptera cilium (Guenee 1852) is one of the grass pests in green space in the southern regions of Iran and many countries around the world. This study was conducted to evaluate the effectiveness of the two Iranian isolates of Beauveria bassiana (Bals.)Vuill including IRAN440C and IRAN441C on S. cilium larvae under laboratory and field conditions. The larvae were reared at 25±10 C, a relative humidity of 60±5%, and a 16:8 h (L:D) photoperiod on grass leaves. The effect of different concentrations of two fungal isolates on second and third larval instars was performed by two methods of larval dipping and grass leaf immersion with spore suspension. The results showed that in both larval instars, the percentage of mortality increased with increasing spore concentration. Based on the mortality rate for both stages, in both methods, the highest percentage of cumulative mortality (51.1%) was observed at a concentration of 5×106 spores of fungi per mL. As the concentration of the suspension increased, a significant decrease in the time required to mortality 50% of the larval population was observed. Our results indicated that the IRAN440C strain of B. bassiana at 5×106 spores of fungi per mL concentration was the most effective strain in terms of toxicity and high mortality in the population of S. cilium. Therefore, this strain can be used in control programs of grasslawn armyworm in urban green space.