Study Of Molecular Method To Detect Resistance To Transgenetic Bt Cottonin In Cotton Bollwarm, Helicoverpa Armigera (Hübner)

The cotton bollworm, Helicoverpa armigera (Hubner), is one of the key pests of the agriculture all over the world. It was hard to control since cotton bollworm developed resistance to lots kind of chemical pesticides last century. As it is specific to pest and is safe to human, Insecticidal crystal proteins (ICPs) from Bacillus thuringiensis (Bt) was used widely to control cotton bollworm. However, the widespread and prolonged exposure to Bt toxins during the plant season of cotton represents one of the largest selections for resistance in cotton bollworm populations the world has ever seen. Cotton industry may be encounted huge disaster if cotton bollworm develops resistance to Bt toxins. So it is important to detect and monitor the resistance to Bt toxin of cotton bollworm.Bioassays have been used to estimate the frequency of Bt resistance alleles of pests, but their failure to distinguish between heterozygote and homozygous susceptible individuals usually necessitates huge sample sizes or multigenerational experiments to detect rare homozygous resistant individuals. Molecular method has several advantages over the traditional methods. First, molecular method can distinguish between heterozygous and homozygous susceptible individuals. Second, molecular method directly detect genetic differences rather than relying on observable phenotypic differences. Third, molecular method also can be used with dead insects in various developmental stages. Further more, molecular method should possess a higher efficiency and flexibility than traditional methods to detect rare individuals with homozygous resistanceOn this research, we analysed the genomic DNA sequences and mRNA sequences both of resistant and suscept strains of cotton bollworm. According to the informations of genomic DNA sequences and mRNA sequences, five primer combinations were designed and screened for detecting resistance to Bt toxin of cotton bollworm. Result of design and screening showed that all of the five preimer combinations can produce specific bands when detecting alleles in cotton bollworm lab-selected strains. However, the resistant band and suscept band of produced by second combination primers were in similar size and were hard to distinguish, so the second combination primers can not use to detect resistance in cotton bollworm field populations. The amplification percent of the first and forth primer combination to detect reistance in lab-selected strains were 100%, but only 75% and 80% to detect resistance in field populations. So, the first and forth primer combination were not suitable to detect resistance in cotton bollworm field populations. The amplification percent of the third and fifth primer combination were 100% both in detecting lab-selected strains and field populations. So, the third and fifth primer combinations were suitable to detect resistance in cotton bollworm field populations.Using the third and fifth primer combination to detect the resistance to transgenetic Bt cotton of cotton bollworm moths which were collected from Qiuxian county, Hebei province, the result showed that there was no resistant allele liked the lab-selected resistant strain allele detected among the 1585 cotton bollworm moths.