Pathogenicity of Certain Indigenous Isolates of Entomopathogenic Fungi against Rice Leaf Folder, Cnaphalocrocis medinalis (Guenee)

The pathogenicity of 42 local isolates of entomopathogenic fungi including Beauveria bassiaua (22), Metarlizium anisopliae (three), M. flavoriride (one), Nomuraea rileyi (four), Paecilomyces sp. (one), Aspergillus spp. (five), Fusarium spp. (three), Zoophthora radiants (two) and Entomoplithora sp. (one) originating from a range of insect species were evaluated against third instar larvae of Cnaphalocrocis medinalis. All the isolates tested were pathogenic to the pest at varying degrees. In single-dose (1 × 10⁷conidia/ml) time-mortality assay, only five isolates of B. bassiaua, viz., BbCm KKL 1100, BbCm TVR 0101, BbCm ADT 0101 (isolated from C. medinalis), BbMp KKL 1195 (isolated from Marasmia partialis) and BbOn KKL 0597 (isolated from Oxya nitidnla), were superior to all other isolates with BbCm KKL 1100 having the lowest LT₅₀ value of 7.81days. In the multiple dose assays (ranging from 1 × 10⁴ to 1 × 10⁹ conidia/ml), the Karaikal isolate of B. bassiaua (BbCm KKL 1100 isolated from C. medinalis) was found to be the most virulent. The LC₅₀ value estimated at 13 days post-inoculation from three independent bioassays for this isolate was 2.8 × 10³ conidia/ml. This was closely followed by BbOn KKL 0597 (isolated from Oxya uitidula) with a LC₅₀ of 2.2 × 10⁴ conidia/ml. Based on the time-dose mortality factor, the B. bassiaua isolate BbCm KKL 1100 has been selected as a potential microbial agent for further investigations in field conditions.