Beauveria bassiana (Bals.) Vuillemin. Pathogenicity to grass-hoppers (Orthoptera: Acrididae). Lethal-time as related to the form and concentration used.

Abstract

The entomopathogenic fungus Beauveria hassiana (Bals.), Vuillemin, strain LARC/FB-192, isolated from naturally infected larvae of Zeuzera pyrina was found pathogenic to grasshoppers. The time required for the pathogen to express its action, as determined from the observed percent mortality, appeared to be related to the form and the concentration used.

High mortality rates of 100% resulted within 7 and 14 days when insects were treated with the dry-spore form (DSP) in either of the two concentrations. Treatment with the higher concentration (4.2 x 107spores/ml) of the spore-suspension form (SPS) led to mortality rates of 82.5 and 87.5% within 7 and 14 days, respectively.

The concentration of the pathogen, within the limits used in this experiment, showed a significant effect on the observed lethal-time (LT50) when used as (SPS). The LT-50 was reduced from >7-days to <3-days as a result of increasing the concentation dose by a hundred-fold (from 3.8 x 105to4.2 x 107 spores/ml).