Investigation of Mass Production Performance and Virulence of Some Entomopathogenic Fungal Isolates and Their Single-Spore Strains Against Rhyzopertha dominica

In this study, mass production performance, germination capacity, and virulence of entomopathogenic fungal isolates belonging to Beauveria bassiana, Metarhizium robertsii, and Purpureocillium lilacinum, along with their corresponding single-spore strains, were evaluated against adults of Rhyzopertha dominica (F., 1792) (Coleoptera: Bostrichidae), a significant stored-product pest. The isolates used in study were 151138 and 5-4 for B. bassiana, F17-2-1 and S3 for M. robertsii, and 31304 and 743 for P. lilacinum. Spores of all isolates were mass-produced using solid-state fermentation technique on rice substrate at 25±2°C. After production, the spores quantity(g), the count of spores per gram, and the total spores count were determined. Germination rates of the spores were assessed after 24 hours of incubation under dark conditions at 25±2°C. For bioassays, spores were applied to R. dominica adults at two concentrations: 2×10¹⁰ and 1×10¹¹spores/kg of wheat. Mortality rates were recorded on the 7th, 14th, and 21st days post-application and were conducted under controlled conditions at 25±2°C, 65±5% relative humidity, and in darkness. According to the mass production results, the highest spore yield was obtained from the S3 sigle-spore strain (M. robertsii) with 8.01 g, while the highest spore count was observed in the 5-4 sigle-spore strain (B. bassiana), with 1.08×10¹¹spores/g. In terms of total spore production, the 5-4 strain was the most successful, producing 4.32×10¹¹spores per 100g of rice. At both tested concentrations, B. bassiana and M. robertsii isolates exhibited higher mortality rates compared to P. lilacinum isolates. Notably, the 5-4 strain achieved 100% mortality on day 14 at the concentration of 1×10¹¹spores/kg of wheat. The findings revealed that the single-spore strains outperformed their original isolates in terms of both mass production capacity and virulence. These results suggest that in vivo passage of entomopathogenic fungi through insect hosts can enhance virulence while also improving production efficiency. Overall, such improvements in fungal isolates may serve as effective tools in biological control strategies and significantly contribute to reducing costs in the development of biopesticides.