Abstract:Field studies were conducted to investigate economic profit of intercropping system of wheat and Bt cotton and its effect on cotton aphids and natural enemies at seedling stage during 2004-2005 in south of Hebei Province. The field experiments consist of wheat intercrop transgenic Bt cotton field (W/CF), transgenic Bt cotton field used chemical insecticides to control cotton aphids only at seedling stage (CCF), and transgenic Bt cotton control field without pesticide use (CF). Each treatment plot was 667m2. Treatments were replicated three times in a completely randomized design. The arthropod collected included cotton aphids (Aphis gossypii Glover), and natural enemies (ladybeetles, spiders and mummified aphids). Wheat and seed cotton yield were also investigated. The results indicated that W/CF significantly suppressed cotton aphids density compared with CF (P<0.05), and obviously reduced the cotton damage by cotton aphids. More natural enemies, especially ladybeetles and mummified aphids, were observed in W/CF than those in CF and CCF, and the peak day of ladybeetle was earlier about 10 days in W/CF than CF. CCF had the highest seed cotton yield, followed by W/CF and CF. However, the total economic income of W/CF was 1.7×104 yuan/hm2 (2004) and 2.08×104 yuan/hm2 (2005), respectively, which were higher than that of CCF and CF. The cotton aphids at seedling stage can signifi- cantly reduce cotton yield and intercropping model could serve as a key tactic in IPM of Bt cotton in nor- thern China.