Isolation and Pathogenicity of Native Beauveria bassiana Isolated from Soil Against Culex Larvae

Abstract Entomopathogenic fungi are important biological control agents for insect pests as they are environmentally friendly and generally safe for non-target organisms and humans. The isolation and identification of native entomopathogenic fungi is essential for developing effective biological control strategies adapted to specific regions. This study investigated the occurrence of entomopathogenic fungi in soil and evaluated the pathogenicity of Beauveria bassiana against Culex mosquito larvae. Three soil samples were collected from different locations within the botanical garden of Abubakar Tafawa Balewa University (ATBU), Bauchi, Nigeria. Entomopathogenic fungi were isolated using the insect baiting technique with Galleria mellonella larvae and cultured on Potato Dextrose Agar (PDA). Morphological identification revealed the presence of Beauveria bassiana in all soil samples, while Metarhizium spp. were recovered from some locations. The pathogenicity of the B. bassiana isolate was evaluated against Culex mosquito larvae using three conidial concentrations (1.8 × 10⁶, 2.45 × 10⁶, and 3.45 × 10⁶ conidia mL⁻¹). Larval mortality increased progressively with increasing conidial concentration and exposure time, ranging from 4% to 100%. Mortality was first observed two days after treatment and was highest at the greatest conidial concentration, whereas no mortality was recorded in the untreated control. Probit analysis showed that the LC₅₀ values decreased from 21.13 × 10⁶ to 3.89 × 10⁶ conidia mL⁻¹ over the five-day exposure period, indicating greater fungal efficacy with prolonged exposure. These findings demonstrate that native B. bassiana isolated from soils of the ATBU botanical garden possesses significant larvicidal activity against Culex mosquito larvae and has considerable potential as an environmentally sustainable biological control agent for integrated mosquito management. Future studies should employ molecular techniques to confirm fungal identity and evaluate the efficacy of native isolates under field conditions.