Screening of High Virulent Isolate of Beauveria spp. against Helicoverpa assulta and Changes in Protective Enzymes Activities of Infected Larvae

摘要

Eleven isolates of Beauveria spp., including B. bassiana (Bb062) newly isolated from Helicoverpa assulta, and other seven B. bassiana isolates and three B. brongniartii isolates that were originally isolated from different geographic origins and various hosts, were tested against the 3rd instar larvae of H. assulta. The protective enzyme activity in the 3rd larvae of H. assulta infected by highly virulent isolate was also assayed. The results showed that the isolate Bb062 had the highest virulence to the 3rd instar larvae among eleven isolates of Beauveria spp., with a corrected mortality reaching 91.07% within 10 d post treatment, and the LT50 was 4.67 d. After inoculated with three concentrations (1.0×10^6, 1.0×10^7 and 1.0×10^8 conidia/mL) of Bb062 conidial suspension, the accumulative mortality of H. assulta larvae increased with the increase of concentration and observation time, and the LC50 was 1.82×10^7 conidia/mL. Activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in H. assulta larvae first increased rapidly then dropped sharply within 72 h. Bb062 showed high virulence to H. assulta and could inhibit activities of protective enzymes. Therefore, it will be a promising biocontrol agent against H. assulta.