Abstract: The physiological effect of quercetin on phenoloxidase (PO) from Tenebrio molitor was determined in vitro and in vivo. The results showed that the inhibition concentration showing 50% of the maximum inhibition (IC₅₀) was 0.625 mmol/L. The PO activity of hemolymph in vivo was increased when the quercetin-DMSO solution or quercetin-water suspension (5 μL) with concentration of 0.2-1.0 mmol/L was injected into the larvae of T. molitor;but the compound would decrease the PO activity when the concentration of quercetin was above 2.0 mmol/L. In addition, the PO activity was also increased when DMSO (5 μL) was injected into the tested insect in vivo.During 2-4 hours after injection of quercetin into the body of the insect, the PO activity was decreased rapidly, then went slowly up and reached the highest level 8 h after injection of the compound, and then dropped again except the low concentration treatment. The results suggest that quercetin at low concentration can cause immune response to the tested insect. When 0.5% BSA was added to the assay system, it had no effect on the PO activity, but could prevent quercetin from sedimentating.

Key words: Tenebrio molitor, quercetin, phenoloxidase, physiological effect