Time-specific infection rate of Beauveria bassiana on Myzus persicae after topical inoculation of conidial suspension

Conidial suspension(5 x 10(6) conidia.ml-1) of the entomopathogenic fungus, Beauveria bassiana BBSG8702 was used to inoculate newly emerged apterous adults of the green peach aphid (Myzus persicae) on detached cabbage leaves in order to measure time-specific infection rate of the fungal agent. The aphids of conidia attached were disinfected using 0.2% chlorothalonil solution at intervals of 8-56 h after inoculation and then maintained at 10 and 20 degrees C for daily observation. There was a significant difference (P < 0.05) in mortality attributed to the fungal infection among the time intervals within 56 h at 10 degrees C after inoculation or within 40 h at 20 degrees C. Compared with the control (not treated with 0.2% chlorothalonil after inoculation), time-specific infection rate at 10 degrees C was estimated as 22.9%, 48.8%, 64.9%, 80.4%, 72.7%, and 98.3% within 8 h, 16 h, 24 h, 32 h, 40 h, and 56 h after inoculation, respectively. The same estimates at 20 degrees C were 31.6%, 48.8%, 58.6%, 86.9%, 97.2%, and 98.7%, respectively. The results indicate that the first 24 h after inoculation was crucial to the infection of B. bassiana to M. persicae. Effective infection with the first 24 h accumulated to 59-65% at 10-20 degrees C.