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

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 3^(rd) instar larvae of H. assulta. The protective enzyme activity in the 3^(rd) 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 3^(rd) instar larvae among eleven isolates of Beauveria spp., with a corrected mortality reaching 91.07% within 10 d post treatment, and the LT_(50) 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 LC_(50) 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.

Optimization of the Solid-phase Fermentation Medium of Metarhizium flavoviride by Response Surface Method

Rice flour, puparium of yellow mealworm, peanut shell and sunflower seed shell are made into the culture medium, and the optimal solid-phase fermen- tation formula for M. flavoviride is figured out. In the solid-phase fermentation, Design-Expert is applied to analyze the significance of all components on the sporu- lotion, and response surface method used to optimize the fermentation medium of M. flavoviride. The results show that puparlum of yellow mealworm is the most sig- nificant component for the sporulation; and the optimal medium formula for the fermentation of M. flavoviride： 0.25-g rice flour, 0. 14-g yellow mealworm pupari- urn, 1.00-g peanut shell, and 0.25-g sunflower seedshell. In this optimal medium, the sporulation achieves 100. 013 × 10^8 spores/mL fungal liquid, 31.7% higher than that of the initial design. Application of the optimal formula will reduce the production cost, obtain higher yield of spores, produce no pollution, and offer tech- nical support for the future large-scale production.