Abstract: The activity changes of phenoloxidase in haemolymph of Helicoverpa armigera larvae parasitized by Ovomermis sinensis were investigated. The results showed that on the first day of infection, the phenoloxidase activity of the infected group increased, which was 1.12 times that of the control group; but in the latter time of infection, the phenoloxidase activity of the infected group was inhibited by the nematodes. On the fifth day of infection, the inhibition reached the highest degree, and the phenoloxidase activity of control group was 1.52 times that of the infected group. Purified with 40% saturated (NH₄)₂SO₄ and Sephadex G-200 gel filtration from the crude enzyme, the phenoloxidase with the purification factor of 41.5, the yield factor of 12.7% and the specific activity of 4 030.6 U/mg was obtained.

Key words: Helicoverpa armigera, Ovomermis sinensis, phenoloxidase, haemolymph, purification