Bio-efficacy of Beauveria bassiana RB PTB against rice bug (Leptocorisa acuta, Thunberg) and brown plant hopper (Nilaparvata lugens, Stål) and its safety to natural enemies

Beauveria bassiana (Balsamo) Vuillemin is an entomopathogenic fungus, ubiquitous in distribution, with a remarkably broad and diverse host range. A new native isolate of B. bassiana RB PTB was obtained from an epizootic observed on rice bugs at the Regional Agricultural Research Station (RARS), Pattambi, Kerala, India. The study aimed to evaluate the bio-efficacy of the new isolate on major sucking pests of rice viz., rice bug, Leptocorisa acuta, brown planthopper (BPH), Nilaparvata lugens and its safety on beneficial insects in the rice ecosystem under laboratory conditions. The isolate was characterized by its high speed of kill, causing 100 % mortality in adult rice bugs and brown planthopper at 120 hr after treatment with a spore concentration of 108 spores mL-1. Probit analysis revealed a time-dependent increase in virulence in rice bugs, with an LC₅₀ of 1.4×10⁸ spores mL-1 at 24 hr after treatment (HAT) and LT₅₀ was 1.63 days at 10⁸ spores mL-1. Additionally, B. bassiana RB PTB (10⁸ spores mL-1) was safe to key natural enemies, including the coccinellid predator Micraspis discolor, long-jawed orb-weaver spider Tetragnatha mandibulata and parasitoids, viz., Goniozus nephantidis, Trichogramma chilonis and T. japonicum. These findings highlight the potential of B. bassiana RB PTB as a promising biocontrol agent against rice bugs and BPH, major sucking pests of rice, while ensuring the safety to natural enemies in the rice ecosystem.