Population dynamic of Bemisia tabaci (Gennadius) from cotton were investigated using samples collected in Changsha from 2009 to 2010. The results indicated that the population density of the insect reached two peaks each year. One peak appeared during May through June and the other in September. Based on analyzing of the mtDNA coI gene sequences, Changsha Bemisia tabaci (Gennadius) population was determined to be biotype Q