By using the headspace collection and GC-MS, the differences in composition and concentrations of volatile allelochemics between transgenic Bt cotton and their parental varieties during various developmental stages were compared and analyzed. The cotton varieties DP5415-NUCOTN33 B, Simian3-GK2 and CCRI16-CCRI30 of both the parental variety and Bt transgenic cotton, were planted in an experimental field of Institute of Plant Protection, CAAS. The following plant parts in cotyledon-, three-leaf-, seven-leaf-...