The insect-resistant activity of Bt cotton has significant variation in different tissue and growing period. Bioassay, the method used to determine the insect-resistant activity of Bt cotton to bollworm inside the country, can not determine the expression levels of Bt protein. The ELISA method established by us resolves this problem. Compared with bioassay, ELISA has the merits of spending shorter time, quantifying Bt toxin protein and easy operation. We find that Bt cotton has different Bt toxin protein content in different tissue and growing period using ELISA method. Leaves and flower petals contain more Bt toxin protein than boll and bracteal leaves. In the late growing period, Bt toxin protein content of every tissue decreases significantly.

The extracted DIMBOA was used to determine its biological activities on the Asian corn borer (ACB), Ostrinia furnscalis (Guenée). The antifeedant property of DIMBOA on ACB was confirmed by the methods of leaf disc (selected and unselected) and feeding-weighing. Antifeeding ratio in unselected experiment was lower than that in selected one. Our results showed that DIMBOA had some effect on embryonic development of ACB and significantly affected the growth and development of ACB's larvae. The larvae's growth and development were delayed, mortality increased, weight of both the larvae and the pupae decreased, sex ratio(f/m) decreased, and deformed pupae appeared after the treatment with DIMBOA. Most ACB holes in plants are at the lower parts of internodes, where DIMBOA concentrations are higher. Further researches on this phenomenum are needed.