No detrimental effect of Bt maize pollen containing Cry1Ab/2Aj or Cry1Ac on adult green lacewings Chrysoperla sinica Tjeder

Adult Chrysoperla sinica Tjeder is a common pollen feeder in maize fields. They are thus directly exposed to insecticidal proteins by consumption of genetically engineered maize pollen containing Bacillus thuringiensis (Bt) proteins. Here we assessed the potential effects of Cry1Ab/2Aj- or Cry1Ac-containing Bt maize pollen on the fitness of adult C. sinica via a dietary-exposure assay under laboratory conditions. Survival, pre-oviposition, fecundity and adult dry weight did not differ between adult C. sinica consuming Bt or the corresponding non-Bt maize pollen. The stability of the Cry protein in the food sources and uptake of the Cry protein by adult C. sinica during the feeding experiment were confirmed by ELISA. These results demonstrate that adult C. sinica are not affected by the consumption of Cry1Ab/2Aj- or Cry1Ac-containing maize pollen, suggesting that production of Bt maize expressing cry1Ab/2Aj or cry1Ac genes will pose a negligible risk to adult C. sinica.     

Degradation of Cry1Ab Protein Within Transgenic Bt Maize Tissue by Composite Microbial System of MC1

Environmental safety issues involved in transgenic plants have become the concern of researchers, practitioners and policy makers in recent years. Potential differences between Bt maize（ND1324 and ND2353 expressing the insecticidal Cry1Ab protein） and near-isogenic non-Bt varieties（ND1392 and ND223） in their influence on the composite microbial system of MC1 during the fermentation process were studied during 2011-2012. Cry1Ab protein in Bt maize residues didn＇t affect characteristics of lignocellulose degradation by MC1, pH of fermentation broth decreasing at initial stage and increasing at later stage of degradation. The quality of various volatile products in fermentation broth showed that no signifi cant difference of residues fermentation existed between Bt maize and non-Bt maize. During the fermentation MC1 efficiently degraded maize residues by 83%-88%, and cellulose, hemicelluloses and lignin content decreased by 70%-72%, 72%-75% and 30%-37%, respectively. Besides that, no consistent difference was found between Bt and non-Bt maize residues lignocellulose degradation by MC1 during the fermentation process. MC1 degraded 88%-89% Cry1Ab protein in Bt maize residues, and in the fermentation broth of MC1 and bacteria of MC1 Cry1Ab protein was not detected. DGGE profi le analyses revealed that the microbial community drastically changed during 1-3 days and became stable until the 9th day. Though the dominant strains at different fermentation stages had signifi cantly changed, no difference on the dominant strains was observed between Bt and non-Bt maize at different stages. Our study indicated that Cry1Ab protein did not infl uence the growth characteristic of MC1.     

转Bt(Cry1Ab)基因对水稻光合特性及光合产物积累的影响

 【目的】明确外源Bt基因插入对水稻倒1叶光合速率及光合作用相关生理特性的影响。【方法】以转Bt基因水稻及亲本水稻为试材,研究盆栽及田间条件下转Bt基因及亲本水稻苗期、拔节期、抽穗期和成熟期倒1叶光合特性及其相关光合酶活性、光合产物积累的动态变化。【结果】转Bt基因及亲本水稻生理活动峰值均出现在拔节期。与亲本水稻相比,转Bt基因水稻苗期叶片净光合速率显著低于亲本;而拔节期和抽穗期,转Bt基因水稻倒1叶净光合速率、叶绿素含量和乙醇酸氧化酶活性显著高于亲本水稻（P＜0.05）,且拔节期转Bt水稻倒1叶气孔导度和胞间CO2浓度也显著高于亲本水稻（P＜0.05）;成熟期,转Bt基因与亲本水稻倒1叶光合特性无显著性差异（P＞0.05）。【结论】与亲本水稻相比,外源Bt基因的插入对水稻叶片光合特性产生短暂影响,但这种影响不具有持续性。     

Expression profiles of Cry1Ab protein and its insecticidal efficacy against the invasive fall armyworm for Chinese domestic GM maize DBN9936

The fall armyworm(FAW) Spodoptera frugiperda, which originated in the Americas, is advancing across China and threatening the nation's maize crops. Currently, one widely used tool for its control is genetically modified(GM) Bacillus thuringiensis(Bt) maize. Sufficient content of Bt protein in appropriate plant parts is crucial for enhancing resistance against insect pests. In this study, we conducted a systematic investigation of Cry1 Ab levels in Chinese domestic GM maize DBN9936, which has recently obtained a biosafety certificate, and evaluated its efficacy against FAW. Quantification of expression levels of Cry1 Ab, via ELISA, indicated a spatio-temporal dynamic, with significant variation of mean Cry1 Ab, ranging from 0.76 to 8.48 μg g–1 FW with the Cry1 Ab protein level ranked as: V6–V8 leafR1 leafR4 leafR1 silkVT tasselR4 kernel. Among the nine locations, the Cry1 Ab levels in DBN9936 of the Xinxiang, Langfang, and Harbin fields were significantly lower than those from Wuhan and Shenyang, and were slightly, but not significantly lower than those from the other four fields. Furthermore, the artificial diet–Cry1 Ab mixture and plant tissue feeding bioassays revealed that DBN9936 has high efficacy against FAW. The insecticidal efficacy of different tissues against FAW larvae reached 34–100% with a descending order of lethality as follows: VT leafR4 leafR1 huskR1 silkVT tasselR4 kernel. Taken together, our results showed that Bt-Cry1 Ab maize DBN9936 has potential as a promising strategy to manage FAW.     

Toxicity and binding analyses of Bacillus thuringiensis toxin Vip3A in Cry1Ac-resistant and-susceptible strains of Helicoverpa armigera(Hübner)

The Bacillus thuringiensis vegetative insecticidal protein, Vip3 A, represents a new family of Bt toxin and is currently applied to commercial transgenic cotton. To determine whether the Cry1Ac-resistant Helicoverpa armigera is cross-resistant to Vip3 Aa protein, insecticidal activities, proteolytic activations and binding properties of Vip3 Aa toxin were investigated using Cry1Ac-susceptible(96S) and Cry1Ac-resistant H. armigera strain(Cry1Ac-R). The toxicity of Vip3 Aa in Cry1Ac-R slightly reduced compared with 96 S, the resistance ratio was only 1.7-fold. The digestion rate of full-length Vip3 Aa by gut juice extracts from 96 S was little faster than that from Cry1Ac-R. Surface plasmon resonance(SPR) showed there was no significant difference between the binding affinity of Vip3 Aa and BBMVs between 96 S and Cry1Ac-R strains, and there was no significant competitive binding between Vip3 Aa and Cry1 Ac in susceptible or resistant strains. So there had little cross-resistance between Vip3 Aa and Cry1 Ac,Vip3A+Cry proteins maybe the suitable pyramid strategy to control H. armigera in China in the future.     

Assessment of the potential toxicity of insecticidal compounds to Peristenus spretus,a parasitoid of mirid bugs

With the increased cultivation of Bt crops in China, Apolygus lucorum and other mirid bugs have emerged as important agricultural pests because they are insensitive to the Bt proteins. In addition, the reduction of pesticide applications after planting Bt crops also increases the severity of mirid bug outbreaks. Peristenus spretus is a parasitoid of mirid nymphs, but its sensitivity to Bt proteins is not known. In the current study, we developed a dietary exposure assay to assess the effects of Bt proteins (Cry1Ab, Cry1Ac, Cry1F, Cry2Aa, and Cry2Ab) on P. spretus adults using a diet consisting of a 10% honey solution with or without Bt proteins at 400 µg g^–1 diet. The results showed that the survival and reproduction of P. spretus adults were reduced by the cysteine protease inhibitor E-64 (a positive control) but were not affected by any of the five Bt proteins. The activities of digestive, detoxifying, and antioxidant enzymes in P. spretus were also unaffected by diets containing the Cry proteins, but they were significantly affected by the diet containing E-64. We then developed a tri-trophic bioassay to determine the effects of the five Bt proteins on P. spretus larvae and pupae. In this assay, A. lucorum nymphs fed an artificial diet containing Cry proteins were used as the hosts for P. spretus. The results of the tri-trophic assay indicated that neither the pupation rate nor the eclosion rate of the P. spretus parasitoids were significantly affected by the presence of high concentrations of Bt proteins in the parasitized A. lucorum nymphs. The overall results indicate that these two assays can be used to evaluate the toxicity of insecticidal compounds to P. spretus and that the tested Cry proteins are not toxic to P. spretus.     

Effect of three insect-resistant maizes expressing Cry1Ie,Cry1Ab/Cry2Aj and Cry1Ab on the growth and development of armyworm Mythimna separata(Walker)

Three transgenic maize events(IE09 S034, Shuangkang 12–5 and C0030.3.5) produced Cry1 Ie, Cry1 Ab/Cry2 Aj and G10-EPSPS, Cry1 Ab and EPSPS, respectively, all of which target the Asian corn borer. The oriental armyworm Mythimna separata(Walker) is the secondary target. In this study, the effects of the three Bt maizes on the development and survival of armyworm were studied. The results showed that IE09 S034 had insecticidal activity against 1 st instar larvae, and the survival rate of armyworm fed with Bt maize for 10 days was 46.2%, significantly lower than that of the control. The larvae at 3 rd–6 th instar were more tolerant of the Bt toxin than the early instar larvae. However, Shuangkang 12-5 had good insecticidal activity against 1 st–5 th instar larvae. The mortality was nearly 100% when the larvae were fed with Shuangkang 12-5 before 3 rd instar, and the toxin had quick-acting efficacy. This event significantly inhibited the development of armyworm; that is, the larval duration of the 3 rd and 4 th instar larvae fed with Shuangkang 12-5 was prolonged by 4.5 and 3.0 days, respectively. The pupal weight and egg number were also significantly lower than those of the control. For C0030.3.5, it could control 1 st–5 th instar larvae effectively. The mortality rates were all over 50% if 1 st–3 rd larvae were fed with this event. The pupal weight of 4 th–6 th instar larvae fed with Bt maize were only 53.9, 56.8 and 54.6%, respectively, compared to that of the control. The number of eggs laid was significantly less than the control. The results indicate that all three transgenic maize events exhibit the potential to provide effective control of early instar larvae of armyworm, which can be commercialized in future to control lepidoptera pests such as Asian corn borer and armyworm.     

苏云金芽孢杆菌杀虫晶体蛋白对棉铃虫活性分析

利用已克隆的5种Bt Cry基因Cry2Ab4、Cry1Ia8、Cry1Ie1、Cry1Ca7、Cry1Cb2和1种野生菌株HD-73(Cry1Ac)表达的6种Bt Cry杀虫晶体蛋白,对棉铃虫进行生物活性分析,并将Cry1Ac杀虫晶体蛋白分别与其它5种Cry蛋白按1:1的比例组合,对棉铃虫进行生物活性测定。结果表明,单独使用Cry1Ac时对棉铃虫活性最高,LC50为3.16μg·mL-1,其次为Cry2Ab4。Cry1Ac与Cry2Ab4组合对棉铃虫也有较高的活性,LC50为48.70μg·mL-1,该组合对棉铃虫的共毒系数为1.21,有相加作用。Cry1Ac与这5种蛋白的组合对棉铃虫都有较高的毒力。     

Genome editing of the SfABCC2 gene confers resistance to Cry1F toxin from Bacillus thuringiensis in Spodoptera frugiperda

ATP-binding cassette transporter C2(ABCC2) is known to be a receptor for Bacillus thuringiensis(Bt) toxins in several lepidopteran insects. Mutations in the ABCC2 gene have been genetically linked to field-evolved resistance to the Cry1 F toxin from Bt in Spodoptera frugiperda. Here we generated a SfABCC2 knockout strain of S. frugiperda using the CRISPR/Cas9 system to provide further functional evidence of the role of this gene in susceptibility and resistance to Cry1 F. Results from bioassays showed that the SfABCC2 knockout S. frugiperda strain displayed 118-fold resistance to Cry1 F compared with the parental DH19 strain, but no resistance to Vip3 A toxin from Bt. These results provide the first reverse genetic evidence for SfABCC2 as a functional receptor for Cry1 F.     

Effects of inhibitors on the protease profiles and degradation of activated Cry toxins in larval midgut juices of Cnaphalocrocis medinalis(Lepidoptera: Pyralidae)

Midgut juice plays an important role in food digestion and detoxification in insects. In order to understand the potential of midgut juice of Cnaphalocrocis medinalis(Guenée) to degrade Bt proteins, the enzymatic activity of midgut juice and its degradation of Bt proteins(Cry2 A, Cry1 C, Cry1 Aa, and Cry1 Ac) were evaluated in this study through protease inhibitor treatments. The activities of total protease in midgut juices were significantly inhibited by phenylmethylsulfonyl fluoride(PMSF), tosyl-L-lysine chloromethyl ketone(TLCK), pepstatin A and leupeptin. The enzymatic activity of chymotrypsin was significantly inhibited by PMSF, and enzymatic activity of trypsin was significantly inhibited by ethylenediaminetetraacetic acid(EDTA), PMSF, tosyl phenylalanine chloromethyl ketone(TPCK), TLCK and trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane(E-64). EDTA could significantly inhibit the degradation of Cry2 A by C. medinalis. EDTA, PMSF, TPCK, and TLCK could inhibit the degradation of Cry1 C and Cry1 Aa. EDTA, PMSF, TPCK, TLCK, and E-64 could inhibit the degradation of Cry1 Ac. Our results indicated that some protease inhibitors hindered various enzymatic activities in the larval midgut of C. medinalis, which may reduce the insect's ability to degrade Bt toxins. These findings may aid the application of protease inhibitors in the management of this insect pest in the future.     

Thrips-mediated impacts from transgenic rice expressing Cry1Ab on ecological fitness of non-target predator Orius tantilus(Hemiptera:Anthocoridae)

Various rice lines have been genetically modified with genes from Bacillus thuringiensis(Bt) to continuously produce Bt insecticidal proteins against lepidopteran larvae. The Bt insecticidal protein constantly expresses in the plants to create an opportunity for non-target herbivores to acquire and convey the protein to their predators or parasitoids across trophic levels. This paper evaluates the effects of Bt rice(namely, Kemindao 1(KMD1) and Kemindao 2(KMD2)) expressing Cry1 Ab as compared to its non-Bt control line, Xiushui 11 on non-target predator Orius tantilus(a generalist predatory anthocorid of thrips) under laboratory and field conditions. To measure several biological parameters such as total nymphal duration and fecundity of this bug, it was reared on thrips and pollens of KMD1 and KMD2 as compared to their control under laboratory conditions. By comparison with the control, Bt rice did not significantly affect main life-history characteristics(total nymphal duration, female adult longevity, oviposition period and fecundity) of this anthocorid preying on Bt rice-fed thrips along with Bt rice pollens, except that the fecundity of this predator for KMD1 was distinctly lower as compared with KMD2 or the control. Enzyme-linked immunosorbent assay(ELISA) results showed that no Cry1 Ab protein was detected in this predator fed on thrips or rice pollen from Bt rice but was in Bt rice pollens. With the beat plate, plastic bag and color trap sampling methods, two-year field monitoring of O. tantilus abundance demonstrated that Bt rice had no significant detrimental effects on the population dynamics and seasonal average densities of this predatory anthocorid as compared with the control. Thus, it is suggested that growing our tested Bt rice(KMD1 and KMD2) producing Cry1 Ab will pose a negligible risk to the anthocorid, O. tantilus.     

转基因植物中Bt Cry2Ab蛋白的抗原表位特征预测(英文)

[目的]通过生物信息学方法了解转基因作物中BtCry2Ab蛋白的二级结构、三级结构、B细胞抗原表位及T细胞抗原表位等结构特征,为今后的抗体设计奠定基础。[方法]以在NCBI数据库中获得Cry2Ab蛋白序列为材料,应用DNAStar中多种方法预测其B细胞表位,并通过在线预测软件NetMHCII2.2分析Cry2Ab蛋白与MHC-II类分子的结合能力从而预测其T细胞抗原表位。[结果]对Cry2Ab蛋白的B细胞抗原表位的预测表明,Cry2Ab蛋白的第208～215区域是潜在的B细胞抗原表位。对Cry2Ab蛋白与MHC-II类分子结合能力的分析表明,Cry2Ab蛋白的第177～185区域、299～307区域和255～263区域是潜在的T细胞抗原表位,暗示含有HLA-DRB10101和HLA-DRB10701等位基因的人群对Cry2Ab蛋白更敏感。[结论]该研究有助于深入了解Cry2Ab蛋白的生物学特征,为完善转基因食品过敏原性的评估方法提供新线索。     

转基因植物中Bt Cry2Ab蛋白的抗原表位特征预测

[目的]通过生物信息学方法了解转基因作物中Bt Cry2Ab蛋白的二级结构、三级结构、B细胞抗原表位及T细胞抗原表位等结构特征,为今后的抗体设计奠定基础。[方法]以在NCBI数据库中获得Cry2Ab蛋白序列为材料,应用DNAStar中的多种方法预测其B细胞表位,并通过在线预测软件NetMHCII 2.2分析Cry2Ab蛋白与MHC-II类分子的结合能力,从而预测其T细胞抗原表位。[结果]对Cry2Ab蛋白B细胞抗原表位的预测表明,Cry2Ab蛋白的第208～215区域是潜在的B细胞抗原表位;对Cry2Ab蛋白与MHC-II类分子结合能力的分析表明,Cry2Ab蛋白的第177～185区域、299～307区域和255～263区域是潜在的T细胞抗原表位,暗示含有HLA-DRB10101和HLA-DRB10701等位基因的人群对Cry2Ab蛋白更敏感。[结论]该研究有助于深入了解Cry2Ab蛋白的生物学特征,为完善转基因食品过敏原性的评估方法提供新线索。     

Polycalin is involved in the action mechanism of Cry2Aa toxin in Helicoverpa armigera(Hübner)

Receptor proteins on the brush border membrane of the insect midgut epithelium are involved in the mode of action of insecticidal Cry proteins from Bacillus thuringiensis(Bt). Polycalin has been identified as a binding protein of the Bt Cry1 Ac toxin in several Lepidoptera including Helicoverpa armigera, but its role in the action mechanism of Cry2 Aa is still unclear. In this study, we investigated the binding characteristics of polycalin from the midgut of H. armigera with Cry2 Aa and its role in the toxicity of Cry2 Aa. The results demonstrated that heterologously expressed H. armigera polycalin peptide could bind with Cry2 Aa with high affinity(K_d=32 nmol L~(–1)). The toxicity of Cry2 Aa decreased by 27% after H. armigera larvae ingested polycalin antisera. These results suggested that polycalin could be a potential functional receptor for Cry2 Aa, and it plays an important role in the susceptibility of H. armigera to Cry2 Aa.     

Impacts of Environmental Factors on Degradation of Cry1Ab Insecticidal Protein in Leaf-Blade Powders of Transgenic Bt Rice

The determination of the environmental fate of Bt insecticidal protein released by Bt rice plants in paddy soils is a key issue in its ecological risk assessment. In this study, the impacts of soil water content, pH, and temperature on the degradation of Cry1Ab protein expressed in the leaves of Bt rice KMD2 were studied in the laboratory. Three types of paddy soils were used, i.e., blue clayey paddy soil, pale paddy soil on quaternary red soil, and marine-fluvigenic yellow loamy paddy soil. Ground powders of KMD2 leaf blades were mixed with each type of soil, and degradation dynamics of Cry1Ab were measured using enzyme-linked immunosorbent assay (ELISA). The degradation rate of Cry1Ab was high at the early experimental stage, but slowed down steadily at middle and later stages, which could be described by exponential equations, with the half-life period of degradation determined as 1.8-4.0 d. The soil water content, pH, and temperature could affect the degradation of Cry1Ab, but the effects of soil pH and temperature were relatively greater. In general,Cry 1 Ab degradations were slower under lower soil pH and temperature conditions, especially for marine-fluvigenic yellow loamy paddy soil.     

转双价抗虫基因(Cry1Ac+Cry2Ab棉靶标害虫不防治环境下检测技术和生存竞争能力研究

[目的]为国家转双价抗虫基因(Cry1Ac+Cry2Ab)棉环境安全评价技术的建立提供参考。[方法]在靶标害虫不防治的环境下,以杂交抗虫棉赣棉杂1号(CK1)和非转基因棉赣棉11号(CK2)为对照,对转双价抗虫基因(Cry1Ac+Cry2Ab)棉进行生存竞争能力研究。[结果]转双价双Bt基因抗虫棉与2个对照相比未显示抗虫优势;在株高、覆盖度、果枝层数、单铃壳重方面无显著竞争优势;在单铃籽棉重、单铃皮棉重、衣分率方面表现显著或极显著负竞争优势;在单株成铃、脱落率、籽棉产量方面与CK1相比无显著竞争优势,与CK2相比表现极显著和显著竞争优势;在皮棉产量方面与CK1相比表现极显著负竞争优势,与CK2相比表现极显著竞争优势。[结论]转双价双Bt基因抗虫棉推广种植可行性为一般。该项检测技术和评价方法有较好的适用性。     

用人工合成多肽作为半抗原制备Bt Cry1Ac的单克隆抗体

为了制备Bt Cry1Ac特异性单克隆抗体(MAB),本试验从NCBI获得了Bt Cry1Ac蛋白的氨基酸序列,根据抗原性、亲水性和表位性分析选定Bt Cry1Ac特异性肽段进行人工合成,并将其偶联于匙孔血蓝蛋白（KLH）免疫动物,应用细胞融合技术制备了抗该肽段的杂交瘤细胞34株。通过ELISA和免疫印迹试验从中筛选出与Bt Cry1Ac天然蛋白产生特异性反应的单克隆抗体杂交瘤细胞株一株（6G9）。ELISA和免疫印迹试验结果显示,该克隆株所分泌的MAB能对合成肽和Bt Cry1Ac产生特异性反应,而与同源的Bt Cry1Aa、Bt Cry1Ab天然蛋白均无交叉反应。通过对转基因棉花的ELISA 检测结果表明,本试验所制备的Bt Cry1Ac单克隆抗体能够有效的区分常规棉和抗虫棉,并且能对其中的Bt Cry1Ac蛋白进行特异性的识别。     

转双价双Bt基因(Cry1Ac+Cry2Ab)抗虫棉栽培地生存竞争能力研究

为建立国家转双价双Bt抗虫基因棉环境安全评价技术,对转双价双Bt基因(Cry1Ac+Cry2Ab)抗虫棉栽培地生存竞争能力进行研究,结果表明,转双价双Bt基因棉花与对照赣棉11相比,各生育期株高生长具有显著竞争优势,优势值3.48～4.75 cm;吐絮期棉覆盖度竞争优势超对照46.77个百分点,达显著水平;产量竞争力优势籽棉超对照1 013.85 kg/hm2,皮棉超对照433.20 kg/hm2,均未达到显著水平;发芽率竞争优势极显著,超过对照2.75个百分点。与非转基因常规棉相比,转双价双Bt抗虫基因棉生存竞争能力优势显著。     

转Bt基因玉米对亚洲玉米螟的抗性评价

转Bt基因抗虫玉米为诺华公司含Bt11转化系的杂交种NX4777,能全株表达Cry1Ab杀虫蛋白,以其非转基因受体玉米品种NX4906为对照。在玉米生长至心叶中期(50~60cm高)、抽雄前期和抽丝散粉期分别进行人工接亚洲玉米螟[Ostriniafurnacalis(Guenée)]初孵幼虫40~60头。以食叶级别、存活幼虫数、蛀孔数、隧道长度和雌穗被害级别等,分别作为评价玉米心叶期和穗期的抗性标准。结果表明,Bt玉米食叶级别仅为1级,显著低于对照的7级。Bt玉米平均每株存活幼虫0.04~0.20头、蛀孔0.11~0.15个、隧道长度0.13~0.41cm,雌穗被害级别为0,植株折茎率为0,而对照玉米平均每株存活幼虫6.19~12.41头、蛀孔4.48~7.05个、隧道长度12.41~24.09cm,雌穗被害级别为5.9,植株折茎率高达73.6%~95.5%。室内生测结果亦表明,取食Bt玉米心叶、雄穗的初孵幼虫3d全部死亡,取食花丝7d死亡率达到99%,相比之下取食常规玉米的存活率在88.7%以上。表明表达Cry1Ab杀虫蛋白的Bt对亚洲玉米螟具有很高的抗虫性,能够保护玉米全生育期免受玉米螟的危害。     

Field Evaluation of the Asian Corn Borer Control in Hybrid of Transgenic Maize Event MON 810

In this study,a transgenic Bt maize hybrid(event MON 810 from Monsanto Company)expressing Cry1Ab protein derived from Bacillus thuringiensis(Bt)and its negative isoline hybrid were evaluatrial. Maize plants were artificially infested with neonate larvae of Asian corn borer at the mid-whorl(firstgeneration),pre-tassel(first-and/or second-generation),and silk(second-generation)growth stages.The transgenic Bt maize hybrid sustained significantly less leaf feeding damage(rating 1.0±0.0)than its negative isoline control(rating 7.3±0.1).With the Bt maize,1.3-6.8%of plants were damaged by corn borer tunneling with＜0.5 cm tunneling per stalk under different levels of infestation,compared with 100%of plants damaged with 9.3-25.0 cm tunneling per stalk for the negative isoline control. On average,transgenic Bt maize hybrids had only 0.01-0.05 tunnels per stalk and no stems were broken.In contrast,the negative isoline control had 3.11-8.36 tunnels per stalk and 31.2-73.9% of stems broken.Yields were significantly higher in trahsgenic Bt maize than in the control. These results demonstrate that transgenic Bt maize can significantly minimize yield losses caused by the Asian corn borer through resistance to the first-and second-generation larvae.