Effects of High Temperature and Ultraviolet-C Irradiance on Conidial Viability and Density of Beauveria Bassiana and Metarhizium Anisopliae Isolated from Soils of Lowland Ecosystems in Indonesia

Abstract

Beauveria bassiana and Metarhiziumanisopliae are the most common entomopathogenic fungi used as biocontrol agents for controlling insect pests. Entomopathogenic fungi have some drawbacks in the field due to their intolerance of high temperatures and ultraviolet-C (UV-C) irradiance. The objective of this research was to evaluate the conidial viability and density of B. bassiana and M. anisopliae isolates when exposed to high temperature and UV-C irradiance. The first experiment, isolates were incubated for 7 d at temperatures of 27, 30, 33, and 36°C. The second one, four intensity levels of UV-C irradiance tested were 5000, 15000, 20000, and 30000 mW/m2. Both B. bassiana and M. anisopliae isolates displayed high conidial viability and density at temperatures of 27, 30, and 33°C, but at 36°C, all isolates died. All isolates tolerated UV-C irradiances of 5000 to 20000 mW/m2, but three of the 18 B. bassiana isolates (16.67%) died at 20000 mW/m2. Three isolates of B. bassiana produced conidia at a UV-C irradiance of 20000 mW/m2, and viable conidia were found after 48 h of incubation. All isolates died after exposure to a UV-C irradiance of 30000 mW/m2. In conclusion, both M. anisopliae and B. bassiana showed high conidial viability and density at temperatures up to 33°C and were tolerant of UV-C irradiance up to 20000 mW/m2.