Abstract: The optimum reaction conditions, sensitivity to the inhibitor and the developmental changes of tyrosinase in the diamondback moth, Plutella xylostella (L.), were studied using time-driving dynamic method. The results showed that the optimum pH of tyrosinase is about 6.4; The OD₄₂₀ values are linear with time from 0-2 min. When stored at 22℃ and 4℃, the prepared tyrosinase could keep its best activity for 12 h and 72 h, respectively; and while stored at -20℃, the tyrosinase could keep its activity for at least 7 days. The activity of tyrosinase in different developmental stages of P. Xylostella follows the order pharate pupa>4th instar larvae >pupa>1st－3rd instar larvae > adult. The I₅₀ of phenyl thiourea (PTU) to the activity of tyrosinase from both the resistant and susceptible strains showed no obvious difference (1.1796 μmol/L and 1.2795 μmol/L, respectively).

Key words: Plutella xylostella, tyrosinase, 　biochemical c haracteristics