Comparative Susceptibility of Different Grub Stages to the Local Strain of Beauveria bassiana
Beauveria bassiana isolated locally from the larvae of Bombyx mori was evaluated at different concentrations viz. 1x108, 1x106, 1x104 and 1x102 spore mL-1 against white grub (Holotrichia sp.) for dose optimization of this fungus. It was observed that among these concentration 1x108 spore mL-1 was the most promising one, showing initial mortality very early and cent per cent in a shorter period of time. The mortality in general in each treatment was recorded in the order of 1x108, 1x106, 1x104 and 1x102 spore mL-1. This spore concentration viz. 1x108 of B. bassiana was tested against different stages of white grub (Holotrichia sp. ) to determine the comparative susceptibility of different stages to this fungus. It was observed that initial (56.66%) mortality occurred on 4th day and cent percent on the 10th day, respectively in case of 1st instar. The initial mortality (46.66 and 43.33%) in 2nd and 3rd instars was recorded on 4th and 6th day and 100% mortality on 12th and 16th day, respectively. These results showed that 1st stage grubs were more susceptible followed by 2nd and 3rd instar grubs.
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