Germination and Culturability after UV Irradiation of Metarhizium anisopliae Native from Soils of Tropical Cattle Farms

The use of entomopathogenic fungi (EF) is a promising alternative for the control of Rhipicephalus microplus, an important tick affecting cattle globally. This study aimed to evaluate the effect of ultraviolet irradiation (UV) exposure on the percentage of conidia germination and number of colony-forming units of eight strains of Metarhizium anisopliae (MaV55, MaV35, MaV31, MaV25, MaV13, Ma08, MaV05, and MaV02). The UV (UV-A and UV-A+B) irradiation was carried out with an ultraviolet radiation emission lamp. The conidia of each strain were exposed to the UV irradiation treatments for 3 h. MaV25, MaV08, MaV05, MaV13, and MaV31 showed higher tolerance to UV-A radiation exposure, as assessed by conidia germination. UV-A+B radiation decreased the germination percentage of all the M. anisopliae strains. The eight evaluated strains showed good tolerance to UV-A radiation, as assessed by the development of colony-forming units (CFU). UV-A+B radiation did not significantly affect (p > 0.05) the count of the CFU of six of the M. anisopliae strains evaluated (MaV35, MaV13, MaV08, MaV05, MaV31, and MaV02). The novel findings of the UV-tolerant M. anisopliae strains may potentially improve the effectiveness of EF under environmental conditions. Integral research under real tropical conditions is advised to evaluate the effectiveness of the EF strains.