| The Asian corn borer(ACB),Ostrinia furnacalis(Guenée),is one of the most serious pests of maize throughout the country in China.The transgenic maize which can express Bacillus thuringiensis(Bt)toxins effectively in the whole development stage provide a new approach for the control of target pest,has been widely grown commercially in more than 20 countries including North America,South America&West Europe for the control of lepidoptera pests such as Ostrinia nubilalis(Hübner).These production practices have revealed that large-scale and prolonged adoption of single toxin transgenic maize will inevitably lead to the development of resistance to Bt insecticidal protein under intensive selection pressure and eventually threaten the sustainable utilization of the transgenic insect-resistant maize.The key to avoid or delay the evolution of target insect resistance and maintenance the benefits of employing the transgenic Bt maize is the rational implementation of resistance strategies,timely and effectively resistance monitoring to the field pest populations will be critical.In order to provide data support for the research and application of transgenic insect resistant maize in China,this paper mainly carried out two aspects of research.(1)The baseline susceptibility of 25 geographical ACB populations in China was established through the determination of the susceptibility of ACB population to Cry1Ab protein by using the surface swabbing method,and the frequency of resistance Cry1Ab alleles of ACB field population was detected by F2 screen.(2)The baseline susceptibility of 6 geographical ACB populations in China was established through the determination of the susceptibility of ACB population to CrylAb/CrylAc fusion protein by using the surface swabbing method.The insecticidal efficacy and the levels of CrylAb protein expressed in whorl leaves of the transgenic cry1Ab/cry1Ac maize(ZZM030)was evaluated and measured using laboratory bioassay and enzyme-linked immunosorbent assay(ELISA),respectively.The main results are as follows:1.The results of the toxicity determination of Cry1Ab protein to 25 geographical populations were that the range of LC50(50%lethal concentration)&EC50(50%maximal effect concentration)among the populations was 0.86 to 71.33 ng/cm2&0.03 to 10.40 ng/cm2,respectively.Value of LC50&EC50 were both significantly different among these populations.The susceptibility of ACB populations in Huanghuaihai Summer Corn Region and parts of the Northeast China to Cry1Ab protein was relatively low indicating that there was geographical differences of ACB in susceptibility to Cry1Ab protein.2.Resistance CrylAb alleles of 13 ACB populations from 25 geographical populations were detected by F2 screen.Results showed that ACB neonates from all populations could not survive more than 7 days after feeding on the whorl leaves of transgenic cry1Ab maize(Bt11).It demonstrated that there are no viable resistant individuals in field due to the high susceptibility of ACB populations to Cry1 Ab protein.3.The results of the toxicity determination of Cry1 Ab/Cry1Ac protein to 6 geographical populations were that the range of LC50&EC50 among the populations was 1.02 to 12.93 ng/cm2&0.26 to 0.65 ng/cm2,respectively.It suggested that there exist regional differences in susceptibility to Cry1Ab/Cry1Ac protein.4.The insecticidal efficiency of the transgenic cry1Ab/cry1Ac maize(ZZM030)was evaluated using laboratory bioassay.In this study,the survival rate was only 23.6%on the 2nd day when ACB neonates of Bt susceptible strain feeding on the whorl leaves of ZZM030,and none survived on the 4th day comparing to the high survival rate of non-Bt maize(X249)which was 93.1%.The survival rate was 11.1%and 12.5%when neonates of CrylAb and Cryl Ac resistant strain feeding on whorl leaves of ZZM030 on the 6th day,respectively.It was significantly lower(81.9%and 77.8%)than that of neonates feeding on X249.Our results showed that transgenic cry1Ab/cry1Ac maize had good insecticidal efficacy against ACB in whorl leaf stage which could provide effective control on increasing population.5.The expression levels of Cry1Ab protein in whorl leaves of ZZM030,which was determined by ELISA,were 10.62(4-leaf stage)and 2.94(8-leaf stage)μg/g(protein/fresh weight). |
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