Selection of a highly virulent isolate of Lecanicillium attenuatum against cotton aphid

Pathogenicity tests of six isolates of entomogenous fungi collected in Korea, including two isolates of Beauveria bassiana, three isolates of Paecilomyces spp. and one isolate of Lecanicillium attenuatum, were conducted to select for highly virulent isolates against the cotton aphid, Aphis gossypii. An isolate of L. attenuatum CS625, had the highest virulence against A. gossypii when the host was treated with either conidia or blastospores of the fungus. The median lethal time (LT50) with either conidial or blastospore treatments of L. attenuatum CS625 to A. gossypii was 2.7 and 3.3 days, respectively and this was shorter than treatments with the other isolates. Mortality caused by L. attenuatum CS625 was dependent on temperature, relative humidity and conidial concentration. Mortality 5 days after treatment with 108 conidia/ml was 100% at 25 and 30 °C. Infection required over 97% RH for 100% mortality, and this isolate was unable to infect cotton aphid at a relative humidity below 75%. This isolate shows promise for development as an alternative control agent for use against the cotton aphid in Korea.