Entomopathogenic fungi play a pivotal role in pest management, and Beauveria bassiana is one of the most important microbial pathogens in the regulation of insect pests. A study was conducted to isolate and characterise a native B.bassiana with potential as a biological control agent against rice bug, Leptocorisa acuta. A new isolate was obtained from an epizootic observed on rice bug, a major pest of rice in Kerala, India. The fungus was identified as a new isolate of Beauveria bassiana (Bals.) Vuill. (Ascomycota: Hypocreales) based on morphological studies. Conidiophores were densely clustered with sub-globose to flask-shaped vesicles and zigzag rachis, hyaline, aseptate hyphae (~ 3.44 μm), and globose-to-subglobose smooth conidia (~ 3.38 × 2.56 μm). The molecular analysis of the fungus revealed the highest similarity with B. bassiana , and the sequence has been deposited in NCBI with accession number OP023314 as B. bassiana RB PTB. The optimum temperature and pH for the growth and sporulation of the new isolate were 27 °C and 6, respectively. Bioassays using conidial suspensions (10³ to 10⁸ conidia mL − 1 ) demonstrated dose- and time-dependent mortality, with 10⁸ conidia mL − 1 , 100% mortality was achieved at 120 h. The corresponding LC₅₀ values decreased from 1.4 × 10⁸ at 24 h to 3.4 × 10¹ conidia mL − 1 at 168 h, and LT₅₀ ranged from 1.63 days at 10⁸ conidia mL − 1 to 4.67 days at 10³ conidia mL − 1 . Scanning electron microscopy (SEM) revealed progressive infection in adults of L. acuta with conidial adhesion at 24 h post-inoculation (hpi), conidial germination and germ tube formation and appressoria development at 48 hpi, hyphal proliferation at 72 hpi, extrusion of hyphae at 120 hpi followed by extensive mycelial networking on cadavers at 168 hpi. These results established the virulence of B. bassiana RB PTB and its potential to uplift as a biocontrol agent against rice bug, L. acuta .
Sreeja et al. (Mon,) studied this question.