Impacts Of New Transgenic Cotton On Arthropod Community In Cotton Field And F₂ Screen Of Resistance Alleles In Helicoverpaarmigera To Bt Toxin Cry2Ab

As an important economic crop in China,the cotton yield is No.1 around the world for many years.But the main threat to cotton production is cotton bollworm,Helicoverpa armigera?Hubner?,which causes serious damage to cotton.For a long time,the spraying of insecticides is the main control to this pest.But the bollworm could develop resistance to those insecticides quickly for its special biological characterization.In the late 1980s to the early 1990s,the outbreak of resistance caused a great loss of cotton.With the rapid development of modern agricultural science and technology,Bt cotton?the first generation of transgenic cotton with Cry1Ac toxin gene?began to be planted in 1997.For its effect to the cotton bollworm,the planting area of Bt cotton is expanding rapidly.By 2014,the area Bt cotton has reached to 3.9 million hectares,accounting for 93%of total cotton of China.With the wide application of Bt cotton,the population of cotton bollworm has been controlled effectively.And also the Bt cotton reduces the use of chemical pesticides,improves the agricultural ecosystem,and shows up the obvious economic benefits,social benefits and environmental benefits.The high dose/refuge strategy is being presented for the resistance management at the beginning of the use of Bt cotton,to kill the possible resistant homozygous and keep the susceptible homozygous.Then the pyramide strategy with the application of two Bt genes?CrylAc/Cry2Ab?is introduced.But the Bt cotton also has the resistance problem for the quickly increasing selection pressure to cotton bollworm.It's necessary to find a new anti-insect strategy.The transgenic RNAi cotton which could express the dsRNA to knock down the key genes for insect in cotton becomes the latest choice.In this study,the impacts on arthropod of new transgeneic cotton?dsRNA cotton?,which express the dsRNA of insect hormone related gene to interfere the growth of bollworm,was investigated to evaluate the bio-safety.And the F₂ screens of resistance alleles to Cry2Ab on different field strains were conducted.The results are helpful to the development of trangenicment cotton and Bt resistance management of H.armigera.1.Impacts of new transgenic cotton on arthropod community in cotton fieldThe new transgenic cotton is based on RNAi technology.To evaluate the inpacts on target pest,non-target pests and natural enemies is an important content of the bio-safety assessment of transgenic cotton,and to some extent this result could determine the future application prospect.This study is based on the investigation of arthropld community in conventional cotton,Bt cotton and new transgenic cotton.The composition of arthropod community is compared and the diversity index,dominance index and richness index of different cotton is set up to evaluate the bio-safety.There is no difference between the composition of arthropod community and these biological parameters,except that number of the chewing mouthparts pests in conventional cotton is significantly higher than other cotton.Therefore,the new transgenic cotton has no side-effects on the non-target pests and natural enemies in cotton field.But based on our result,the effect of new transgenic cotton to cotton bollworm is not as good as the Bt cotton.2.F₂ screen of resistance alleles of H.armigera to Bt toxin Cry2Ab.In 2014,F₂ screen of resistance alleles of H.armigera to Bt toxin Cry2Ab was conducted on the field populations from Anyang of Henan,Xiajin of Shandong,Langfang of Hebei,Shawan of Xinjiang.On the Anyang population,the number of single female line is 251,there are 11 resitant single female lines in 109 detected lines,and the resistance allele frequency is 0.025.On the Xiajin population,the number of single female line is 176,there are 6 resitant single female lines and 7 resistance alleles in 63 detected lines,and the resistance allele frequency is 0.028.On the Langfang population,the number single female line is 350,there are 14 resitant single female lines in 58 detected lines,and the resistance allele frequency is 0.060.But for the Shawan population,the number of single female line is 150 and there is no resistant single female line in 77 detected lines.So the resistance allele frequency for this population is 0.000.Based this result,it could be found that the frequency of resistance alleles is higher in North China cotton areas which have a longer history for planting Cry1Ac cotton than that in Northwest China.