The Resistance Gene Frequency To Cry1Ac Toxin In Helicoverpa Armigera Populations Collected From Bt Cotton Planting Region Of Northern China

Insect resistant transgenic crops, such as Bt cotton, Bt maize, and Bt potatoes, have become important tools in the globe control of insec pests. Like chemical insecticide, Continuous production of Bt toxin in transgenic plants leads to season-long selection for insect resistance to the Bt insecticidal protein. Laboratory population of at least ten specias of moths, two specials of beetles, and four specials of flies have been exposed repeatedly to Bt more than 50 experiments designed to select for resistance, especially Plutella xylostella development of resistance in the field. The potential risk of Bt resistance in targeted insect pests is threatening the sustainable deployment of Bt crops. Although there are no irrefutable evidence to prove field population of target insect pests to develop resistance to Bt crops, many laboratories have get the strain of pest to Bt crops. Several mentoring methods have been developed in recent years to evaluate early Bt resistance in the field, such as standard bioassay, diagnostic concentration, single pair crossing, p2 screen and molecular methods.Bt cotton has been widely planted in the Yellow River vally of China since 1998.Anci County of Hebei Province and Xiajin County of Shandong Province are two areas where almost 100% of the cotton grown producing CrylAc. These areas were therefore selected for analysis of the frequency of gene coding for resistance to CrylAc in field populations of the bollworm by using diagnostic concentration method, and the resistance inheritance mode was studied also by this method. The results were as follows: In 2002,adult females were collected using light-traps. Females were caged individually and were allowed to lay eggs. At hatch, 25-35 larvae from each female were screened for growth rate on normal artificial diet and on diet contaning l.Oug/ml of CrylAc toxin . This growth rate bioassay was designed to detect non -recessive resistance genes in heterozygous genotypes and to detect recessive resistance genes only when prensent in a homozygous resistant genotypes. The bioassay detected 1 resistant individual out of 234 screened in Anci and 1 resistant individual out of 420 screened inXiajin. These results suggest that a conservative estimate of the resistance gene frequency is 0.001068 in Anci population and 0.00595 in Xiajin population.Some familes in two areas were screened in F2 generation, and result indicated that resistance gene maybe minor genes for CrylAc resistance or less dominant genes for resistance may be at higher frequencies, especially in the Xiajin population.The resitance of the laboratory resistant population of cotton bollworm to CrylAc toxin was determined as an incompletely recessive inheritance controlled by single autosomal allele.This studies screened resistant individual of field population cotton bollworm to CrylAc and estimated resistant gene frequency, and studied the inheritance mode of laboratory resistant to CrylAc, which can provid strategies for pest control and transgenic Bt cotton management.