Day to day changes in the activity of phenoloxidase was examined in the haemolymph of 5th instar silkworm Bombyx mori L during the progress of fungal pathogen Beauveria bassiana. Increased trend of phenoloxidase activity was recorded in haemolymph of both inoculated (0.491 to 0.5 µ moles/mg protein/min) and control (0.456 to 0.473 µ moles/mg protein/min) from the 1st to 3rd day of the instar, then the enzyme activity was declined in the rest of the 5th instar in treated (0.499 µ moles/mg protein/min to 0.142 µ moles/mg protein/min) and control (0.413 µ moles/mg protein/min to 0.200 µ moles/mg protein/min). Significant elevation of phenoloxidase (PO) activity was recorded up to 4th day of the instar then the drastic reduction of the enzyme activity was observed in Beauveria bassiana inoculated silkworm larvae compared to control.
