An experiment was designed to investigate the tolerance and response of the Kosteletzkya virginica (L.) Presl to one-instar bollworms of Helicoverpa armigera (Hubner). In this experiment, the insects obviously brought an enhancement in damaged rate of leaf area (DRLA), average diameter of bitten hole (ADBH) and average grade of leaf damage (AGLD) in K. virginica seedlings. When amount of insect increased to 4 per top leaf, the average DRLA, AABH, ADBH and AGLD were 8.6%, 9.2 mm, 2.7 mm and 2.0 mm, respectively, and the seedlings showed a potential insect-tolerance to this insect stress. Furthermore, with an increase of insect density, MDA, relative permeability of membrane (RPM), O 2 -Á production and soluble sugar concentration all enhanced, whereas activities of SOD and POD increased and subsequently declined. By statistical analysis, it was drawn that biotoxicity of O 2 -Á was the first destroying factor, cell membrane decomposition ranked the second, and the destruction of membrane lipid peroxidation was the slightest to K. virginica seedlings. Moreover, under the insect stress, POD was the most significant factor in protecting the seedlings, soluble sugar acted as the subordinate one, and the protection of SOD was the slightest compared to two others. In addition, insect stress obviously affected chlorophyll-fluorescence characteristics, and resulted in a significant increase in Fo and qN, and a significant reduction in Fv/Fm, ETR and qP during experiment.
