转 Bt 基因水稻对三化螟自然种群的影响

为了了解水稻重要害虫三化螟 Scirpophaga incertulas（Walker）对转 Bt 基因水稻产生抗性的潜在风险,本文利用自然种群生命表,研究了第 3 代三化螟在转Bt基因杂交稻汕优 63 及非转 Bt 基因杂交稻汕优 63 上的种群参数。结果表明：在 Bt 稻上1～2 龄幼虫的存活率为 4.03%,极显著低于非转基因 SY63（55.76%）;Bt 稻上幼虫为害率为1.75%,极显著低 于非转基因 SY63（5.98%）;Bt 稻上存活的幼虫发育历期明显长于非转 Bt SY63。     

Seasonal expression of Bt proteins in transgenic rice lines and the resistance against Asiatic rice borer Chilo suppressalis (Walker)

Laboratory bioassays and field surveys were carried out to compare the resistance of three transgenic rice (Oryza sativa L.) lines including Bt-DL expressing a single gene cry1Ab, Bt-KF6 expressing stacked genes cry1Ac and CpTI genes and Bt-SY63 expressing a fusion gene cry1Ab/cry1Ac, respectively, to an important rice pest Chilo suppressalis (Walker). In addition, enzyme-linked immunosorbent assays (ELISA) were conducted to monitor the Bt protein expressions in rice leaves and stems at different rice growth stages. Results showed that all the transgenic rice lines exhibited significantly high resistance to the pest compared with their corresponding nontransformed isolines. Among the transgenic rice lines, Bt-SY63 and Bt-KF6 had higher resistance to C. suppressalis at early growth stage, but lower resistance at late stages, while the pest resistance of Bt-DL was relatively stable throughout the growing season. The results were consistent with ELISA results showing that Bt protein levels in Bt-SY63 or Bt-KF6 leaves decreased in late growth stages, but were relatively stable in Bt-DL at all growth stages. This demonstrates that the resistance to a pest by Bt plants is positively correlated with Cry protein expression levels in plant tissues. Compared with Bt-SY63 and Bt-KF6, the Bt protein expression levels were significantly lower in Bt-DL, while its resistance to C. suppressalis was the highest. This may suggest that C. suppressalis is more susceptible to Cry1Ab than to Cry1Ac. The data from the current study are valuable for decision-making for commercial use of Bt rice lines and development of appropriate pest control and resistance management strategies for the transgenic rice lines.     

多年种植Bt稻后外源蛋白在土壤中的积累

外源蛋白在环境中的残留与积累是转Bt基因作物环境安全评价的重要内容之一。我国已育成多个具有商业化前景的Bt稻品系,但目前多年种植Bt稻后Bt外源蛋白是否会在土壤中积累还不清楚。本研究在同一试验田连续9年种植了转cry1Ab/1Ac基因明恢63(华恢1号)和转cry2A基因明恢63水稻,采用酶联免疫吸附法(ELISA)跟踪监测了分蘖期和收获后60 d根际土中外源蛋白含量变化,试验第1年(2012年)和最后1年(2020年)还测定了苗期、开花期和成熟期根际土中外源蛋白含量。结果表明: 2012年,转cry1Ab/1Ac基因明恢63在苗期、分蘖期、开花期、成熟期和收获后60 d根际土中外源蛋白含量分别为1.25、1.77、1.97、1.71和0.30 ng·g^-1,2020年分别为1.30、1.69、2.03、1.77和0.43 ng·g^-1;2012年,转cry2A基因明恢63在苗期、分蘖期、开花期、成熟期和收获后60 d根际土中外源蛋白含量分别为0.91、1.52、1.53、1.37和0.12 ng·g^-1,2020年分别为0.95、1.43、1.61、1.40和0.15 ng·g^-1。多因素方差分析显示,时间效应对Bt外源蛋白积累不显著,而品种和生育期效应显著。Bt稻生长过程中根际土中可以检测出微量的Bt外源蛋白,但收获后60 d已经基本降解完毕,根际土中Bt外源蛋白含量不会随着种植时间的增加而累积。     

Field performance of transgenic elite commercial hybrid rice expressing bacillus thuringiensis delta-endotoxin

Here we describe development of transgenic elite rice lines expressing a Bt fusion gene derived from cryIA(b) and cryIA(c) under the control of rice actinI promoter. The lines used in the study were indica CMS restorer line of Minghui 63 and its derived hybrid rice Shanyou 63. The level of Bt fusion protein CryIA(b)/CryIA(c) detected in Minghui 63 (T51-1) plants was 20 ng/mg soluble protein. The Bt Shanyou 63 was field-tested in natural and repeated heavy manual infestation of two lepidopteran insects, leaffolder and yellow stem borer. The transgenic hybrid plants showed high protection against both insect pests without reduced yield.     

转cry1Ab基因抗虫水稻的田间试验

采用农杆菌介导的遗传转化技术, 将Bt基因cry1Ab导入三系恢复系明恢63获得了一批抗虫性及农艺性状较好的转基因纯合株系。研究中, 进一步检测了这些纯合株系的拷贝数、Bt蛋白含量、抗虫性及主要农艺性状。结果显示: 5个转基因纯合株系均为单拷贝; 纯合株系T_1Ab-10及其杂种的Bt蛋白含量最高; 人工接虫和自然感虫试验中, T_1Ab-10对二化螟、三化螟和稻纵卷叶螟均表现高度抗性; 喷药试验中, 阳性植株与阴性植株、对照植株的主要农艺性状均没有显著差异。这说明转cry1Ab基因纯合株系T_1Ab-10具商品化潜力, 可作基因聚合材料。     

转修饰cry1Ac基因籼稻明恢81经花药培养获得抗虫DH系

对基因枪法获得的明恢81转修饰的cry1Ac基因当代植株进行花药培养,共接种花药2600枚,获得83份花培植株,其中双倍体植株43份,单倍体植株40份,PCR结果表明含有cry1Ac基因的植株55份,花培植株群体中转基因与非转基因植株的比值为2：1（55／28）,进一步结合Southern blot和ELISA分析,于花培植株当代筛选到转基因纯合株系36份,外源蛋白表达量上,花药来源于同一克隆的DH系的不同植株之间基本一致,最高的Cry1Ac含量达0．25％,田间抗虫性试验表明,经花药培养纯合获得的部分转基因纯合系植株对二化螟（chilo suppressalis)表现出高抗,而且主要农艺性状保持不变,以上结果表明水稻花药培养可以加速转基因的纯合与良种利用。     

Bt水稻对田间非靶标害虫种群动态的影响

以转cry1Ab/cry1Ac基因水稻汕优63(以下简称汕优63/Bt)为材料,亲本汕优63(以下简称汕优63/CK)为对照,在田间自然感虫条件下研究汕优63/Bt对稻田几种非靶标害虫种群消长动态的影响。结果表明,汕优63/Bt上稻苞虫Pelopidas mathias(Fabricius)和稻眉眼蝶Mycalesis gotamaMoore幼虫数量都显著低于对照品种,但汕优63/Bt对稻苞虫的毒性强于稻眉眼蝶。汕优63/Bt上稻飞虱(白背飞虱Sogatellafurcifera(Horvath)和褐飞虱Nilaparvatalugens(Stal))混合种群数量通常与对照品种基本一致,在少数调查时间显著高于对照品种。相反,除少数调查时间与对照品种没有显著差异外,稻叶蝉(黑尾叶蝉Nephotettixcincticeps(Uhler)和二点黑尾叶蝉N.viriscens(Distant))混合种群数量通常显著高于对照品种。稻飞虱和叶蝉成为汕优63/Bt上的主要害虫。     

Bacillus thuringiensis delta-endotoxin binding to brush border membrane vesicles of rice stem borers

The receptor binding step in the molecular mode of action of five delta-endotoxins (Cry1Ab, Cry1Ac, Cry1C, Cry2A, and Cry9C) from Bacillus thuringiensis was examined to find toxins with different receptor sites in the midgut of the striped stem borer (SSB) Chilo suppressalis (Walker) and yellow stem borer (YSB) Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae). Homologous competition assays were used to estimate binding affinities (K(com)) of (125)I-labelled toxins to brush border membrane vesicles (BBMV). The SSB BBMV affinities in decreasing order was: Cry1Ab = Cry1Ac > Cry9C > Cry2A > Cry1C. In YSB, the order of decreasing affinities was: Cry1Ac > Cry1Ab > Cry9C = Cry2A > Cry1C. The number of binding sites (B(max)) estimated by homologous competition binding among the Cry toxins did not affect toxin binding affinity (K(com)) to both insect midgut BBMVs. Results of the heterologous competition binding assays suggest that Cry1Ab and Cry1Ac compete for the same binding sites in SSB and YSB. Other toxins bind with weak (Cry1C, Cry2A) or no affinity (Cry9C) to Cry1Ab and Cry1Ac binding sites in both species. Cry2A had the lowest toxicity to 10-day-old SSB and Cry1Ab and Cry1Ac were the most toxic. Taken together, the results of this study show that Cry1Ab or Cry1Ac could be combined with either Cry1C, Cry2A, or Cry9C for more durable resistance in transgenic rice. Cry1Ab should not be used together with Cry1Ac because a mutation in one receptor site could diminish binding of both toxins.     

转Bt基因抗虫玉米对亚洲玉米螟幼虫取食行为的影响

室内研究了转cry1Ab杀虫蛋白基因的Bt抗虫玉米MON81 0和Bt1 1对亚洲玉米螟Ostriniafurnacalis初孵幼虫和3龄幼虫的取食行为、取食选择性和存活率的影响。在48h的非选择性试验中玉米螟初孵幼虫在MON81 0和Bt1 1玉米心叶组织上的幼虫取食率随时间的增加而下降,在对照玉米上的幼虫取食率随时间的增加而上升,两者间差异极显著。初孵幼虫接虫到MON81 0和Bt1 1玉米叶片48h的累计死亡率分别为67 .5 %和47 .5 % ,而在对照玉米上死亡率均为0. 3龄幼虫在Bt和非Bt玉米穗轴组织上的幼虫取食率随时间的增加呈上升趋势,第48h时在Bt和非Bt玉米上的幼虫取食率分别达到77 5 %和1 0 0 % ,差异极显著。选择性试验中,第4～48h内,初孵幼虫在Bt玉米上的幼虫取食率呈下降趋势,第48h时MON81 0和Bt1 1与各自非Bt对照的组合中初孵幼虫的累计死亡率分别为2 5 .0 %和1 7. 5 % ,二者差异不显著。3龄幼虫在Bt玉米和非Bt玉米上的幼虫取食率均随时间的延长而增加,但在非Bt玉米的幼虫取食率增加速度快,与Bt玉米差异极显著。Bt玉米对玉米螟幼虫取食有抑制和忌避作用。     

转cry1Ab/cry1Ac基因玉米Cry1Ab/Cry1Ac融合蛋白表达及对亚洲玉米螟的室内杀虫效果

【目的】室内抗螟性评价是转Bt基因抗虫玉米研发和安全性评价的重要环节。【方法】采用酶联免疫吸附测定法(ELISA)测定了转cry1Ab/cry1Ac基因玉米ZZM030心叶中Cry1Ab/Cry1Ac融合杀虫蛋白的表达量;采用室内生测法测定了分别取食转基因玉米ZZM030和非转基因玉米X249心叶后亚洲玉米螟Ostrinia furnacalis敏感品系ACB-BtS、Cry1Ab抗性品系ACB-AbR和Cry1Ac抗性品系ACB-AcR初孵幼虫的存活率。【结果】转基因抗虫玉米ZZM030 4叶期和8叶期心叶中Cry1Ab/Cry1Ac融合杀虫蛋白的表达量分别是10.62和2.94 μg/g FW。敏感品系亚洲玉米螟初孵幼虫取食转基因玉米ZZM030心叶2 d的存活率仅为23.6%,4 d后存活率为0,而取食非转基因对照玉米X249心叶4 d的存活率高达93.1%。Cry1Ab抗性品系和Cry1Ac抗性品系初孵幼虫取食转基因玉米ZZM030心叶6 d后的存活率分别为11.1%和12.5%,而取食非转基因玉米X249心叶6 d后的存活率分别为81.9%和77.8%。【结论】转cry1Ab/cry1Ac基因玉米ZZM030心叶中高表达的Cry1Ab/Cry1Ac融合蛋白对亚洲玉米螟初孵幼虫具有极高的杀虫效果。     

Effect of plant age, larval age, and fertilizer treatment on resistance of a cry1Ab-transformed aromatic rice to lepidopterous stem borers and foliage feeders

The resistance of vegetative, booting, and flowering stage plants of a variety of an aromatic rice, Oryza sativa L., transformed with a Bacillus thuringiensis Berliner cry1Ab gene under control of the maize phosphoenolpyruvate carboxylase (PEPC) promoter was evaluated against four lepidopterous rice pests--the stem borers Chilo suppressalis (Walker) (Lepidoptera: Crambidae) and Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae), and the foliage feeders Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) and Naranga aenescens Moore (Lepidoptera: Noctuidae). Plants of the cry1Ab-transformed line (no. 827) were more resistant to young larvae of S. incertulas, C. suppressalis, and C. medinalis than control plants at the vegetative stage but not at the flowering stage. Survival of 10-d-old stem borer larvae did not differ on cry1Ab plants and control plants at either the vegetative or flowering stage, but the development of 10-d-old C. suppressalis larvae was retarded on the vegetative stage cry1Ab plants. Immunological analysis also showed an apparent decline in Cry1Ab titer in leaf blades and leaf sheaths at the reproductive stage. In experiments comparing three fertilizer treatments (NPK, PK, and none), there was a significant interaction between fertilizer treatment and variety on larval survival only in whole-plant assays at booting stage with C. suppressalis. On cry1Ab plants, larval survival did not differ significantly among the three fertilizer levels, whereas on control plants survival was highest with the NPK treatment. cry1Ab plants tested at the sixth and seventh generations after transformation were more resistant than control plants to N. aenescens and C. suppressalis, respectively, suggesting that gene silencing will not occur in line 827. The results of the experiments are discussed in terms of resistance management for B. thuringiensis toxins in rice.     

Variant cry1Ab entomocidal Bacillus thuringiensis toxin gene facilitates the recovery of an increased number of lepidopteran insect resistant independent rice transformants against yellow stem borer (Scirpophaga incertulus) inflicted damage

The primary technical constraint plant scientists face in generating insect resistant transgenic crops with insecticidal Bacillus thuringiensis (Bt) crystal protein (Cry) genes remains failing to generate sufficiently large numbers of effective resistant transgenic plant lines. One possible means to overcome this challenge is through deployment of a Cry toxin gene that contains high levels of insecticidal specific activity for target insect pests. In the present study, we tested this hypothesis using a natural variant of the Cry1Ab toxin under laboratory conditions that possessed increased insecticidal potency against the yellow stem borer (YSB, Scirpophaga incertulus), one of the most damaging rice insect pests. Following adoption of a stringent selection strategy for YSB resistant transgenic rice lines under field conditions, results showed recovery of a significantly higher number of YSB resistant independent transgenic plant lines with the variant cry1Ab gene relative to transgenic plant lines harbouring cry1Ab berliner gene. Structural homology modelling of the variant toxin peptide with the Cry1Aa toxin molecule, circular dichroism spectral analysis, and hydropathy plot analysis indicated that serine substitution by phenylalanine at amino acid position 223 of the Cry1Ab toxin molecule resulted in a changed role for α-helix 7 in domain I of Cry1Ab for enhanced toxicity.     

Laboratory and field assessments of prey-mediated effects of transgenic Bt rice on Ummeliata insecticeps (Araneida: Linyphiidae)

One major concern regarding the release of Bt rice is its potential impact through tritrophic interactions on nontarget arthropods, especially natural enemies. We studied the effects of two Bt transgenic rice varieties, TT9- 3 and KMD1, expressing Cry1Ab/Cry1Ac and Cry1Ab, respectively, on a predatory ground spider [Ummeliata insecticeps (B?senberg et Strand)] supplied with Bt rice-fed brown planthopper [Nilaparvata lugens (St?l)] nymphs. Although immunoassays confirmed that U. insecticeps ingested Bt insecticidal protein when supplied with Bt rice-fed N. lugens, no negative effects were found on its survival and development. Furthermore, the fecundity of U. insecticeps fed prey reared on Bt rice was not significantly different from that of those fed prey reared on non-Bt rice. A 3-yr field trial indicated that Bt rice did not significantly affect the population density of U. insecticeps in comparison with non-Bt rice. In conclusion, the Bt rice lines tested in this study had no adverse effects on the survival, developmental time, or fecundity of U. insecticeps in the laboratory or on population dynamics in the field.     

Fitness of Cry1A-resistant and -susceptible Helicoverpa armigera (Lepidoptera: Noctuidae) on transgenic cotton with reduced levels of Cry1Ac

The performance of Helicoverpa armigera (Hübner) on 15-wk-old cotton plants was compared for a susceptible strain, a near-isogenic laboratory-selected strain, and F1 progeny of the two strains. Glasshouse experiments were conducted to test the three insect types on conventional plants and transgenic plants that produced the Bacillus thuringiensis (Bt) toxin Cry1Ac. At the time of testing (15 wk), the Cry1Ac concentration in cotton leaves was 75% lower than at 4 wk. On these plants, < 10% of susceptible larvae reached the fifth instar, and none survived to pupation. In contrast, survival to adulthood on Cry1Ac cotton was 62% for resistant larvae and 39% for F1 larvae. These results show that inheritance of resistance to 15-wk-old Cry1Ac cotton is partially dominant, in contrast to results previously obtained on 4-wk-old Cry1Ac cotton. Growth and survival of resistant insects were similar on Cry1Ac cotton and on non-Bt cotton, but F1 insects developed more slowly on Cry1Ac cotton than on non-Bt cotton. Survival was lower and development was slower for resistant larvae than for susceptible and F1 larvae on non-Bt cotton. These results show recessive fitness costs are associated with resistance to Cry1Ac.     

Resistance to Tecia solanivora (Lepidoptera: Gelechiidae) in three transgenic Andean varieties of potato expressing Bacillus thuringiensis CrylAc protein

Transgenic potato, Solanum tuberosum L., plants containing a synthetic cry1Ac gene coding for the Bacillus thuringiensis (Bt) crystalline insecticidal protein were produced and evaluated for resistance to Tecia solanivora Povolny (Lepidoptera: Gelechiidae), the larvae of which attack potato tubers. In total, 43 transgenic lines of commercial Andean potato varieties Diacol Capiro, Pardo Pastusa, and Pandeazúcar were obtained. These transgenic lines were found to have one to four copies of cry1Ac per genome and expression levels of Cry1Ac protein varying from 0.02 to 17 microg/g fresh tuber tissue. Bioassays of T. solanivora larvae on these transgenic potato tubers showed 83.7-100% mortality, whereas the mortality levels on nontransgenic lines were 0-2.67%. Our data indicate the capability of Bt transgenic technology to control the T. solanivora while reducing the use of chemical insecticides. Further studies under controlled field conditions will be helpful in exploring the potential of CrylAc potatoes in the insect pest management strategies.     

Field evaluation of resistance of transgenic rice containing a synthetic cry1Ab gene from Bacillus thuringiensis Berliner to two stem borers

Two transgenic rice (Oryza sativa L.) lines, KMD1 and KMD2 at the R4 generation, transformed with a synthetic cry1Ab gene from Bacillus thuringiensis Berliner, were first evaluated for stem borer resistance in the field during the rice growing season of 1998 in two areas of Zhejiang Province, China. Both KMD1 and KMD2 were highly resistant to the stem borers Chilo suppressalis (Walker) and Scirpophaga incertulas (Walker), and were completely undamaged during the whole rice growing season. In contrast, damage to the plants of the untransformed parental control (Xiushui 11) was in the form of deadhearts or whiteheads. Under natural infestation by the C. suppressalis, the damage to control plants reached a peak of 88.7% of plants and 20.1% of tillers encountered with deadhearts. Under artificial and natural infestation of neonate striped stem borers at the vegetative stage and booting stage, 100% of plants and 25.6% of tillers, 78.9% of plants and 15.6% of productive tillers among artificially infested control plants were observed with the symptom of deadhearts and whiteheads, respectively. Damage to the control plants from artificial infestation by the S. incertulas reached a peak of 97.0% of plants and 22.9% of tillers damaged. The field research indicated that both KMD1 and KMD2 show great potential for protecting rice from attack by these two stem borers.     

Evaluation of transgenic Bt corn for resistance to the Asian corn borer (Lepidoptera: Pyralidae)

The Asian corn borer, Ostrinia furnacalis (Guenée), is the most important insect pest on corn in China. Bt transgenic corn provides a new tool for Asian corn borer control. Monsanto's YieldGard Bt transgenic corn expressing Cry1Ab protein, and a non-Bt control, were evaluated in Beijing. Laboratory bioassays were carried out by exposing neonates to an agar-free diet containing Bt corn whorl leaves, tassels, and anthers, or by exposing neonates directly to fresh silk and pollen. These are the tissues initially attacked by neonates in the field. All of these tissues, with the exception of pollen, contained sufficient insecticidal protein to kill > or = 95% of larvae within 7 d. Surviving larvae had also not grown beyond first instar and weighed < or = 0.1 mg. Although larvae feeding on Bt corn pollen were significantly smaller than those on non-Bt corn pollen, there was no significant difference in mortality. Field trials were also conducted with artificial infestations of Asian corn borer at mid whorl, late whorl, and silking stages. Damage ratings and number of larvae surviving per plant indicated that Bt corn was highly resistant to Asian corn borer. Therefore, YieldGard offers the potential for season-long protection against first- and second-generation Asian corn borer.     

Expression of Bt cry1Ac in transgenic oilseed rape in China and transgenic performance of intraspecific hybrids against Helicoverpa armigera larvae

The expression of a synthetic Bacillus thuringiensis ( Bt ) cry1Ac gene in oilseed rape (OSR, Brassica napus ) was monitored under field conditions in China, and performance against Helicoverpa armigera larvae was compared in intraspecific hybrids with a Chinese OSR variety. Leaf samples from transgenic OSR were collected at various developmental stages in two separate field experiments. The Bt Cry1Ac concentrations in the third uppermost leaves increased before pod formation stage and either increased or decreased after pod formation stage whereas the total soluble protein increased before and decreased after pod-fill in the later growing season. Spontaneously formed intraspecific hybrids between transgenic OSR and a Chinese conventional OSR were obtained in the field and transgenic status was confirmed by a green fluorescent protein (GFP) phenotype and polymerase chain reaction. A bioassay on the neonate larvae of a susceptible strain of H.   armigera was performed to test the efficacy of Bt Cry1Ac toxin in hybrid OSR plants. Both the original transgenic OSR and hybrid plants had a negative effect on body-weight gain of insect larvae. It was assumed that Bt Cry1Ac toxin concentration was similar in hybrids compared to the original transgenic OSR at the investigated developmental stages. The frequency of hybrid production and volunteerism could potentially enhance the evolution of insect pest tolerance in the field.     

Bacillus thuringiensis protein transfer between rootstock and scion of grafted poplar

Bacillus thuringiensis (Bt) Cry1Ac protein is a toxin against different leaf‐eating lepidopteran insects that attack poplar trees. In the present study, the mode of migration of the Bt‐Cry1Ac protein within poplar grafts was investigated. Grafting was done using Pb29 (transgenic poplar 741 with cry1Ac genes), CC71 (transgenic poplar 741 with cry3A genes), non‐transgenic poplar 741 and non‐transgenic Populus tomentosa, either as scion or as rootstock. In order to detect migration of Bt‐Cry1Ac protein from one portion of the graft union to different tissues in the grafted plant, ELISA analysis was employed to assess the content of Bt‐Cry1Ac protein in the phloem, xylem, pith and leaves of the grafted poplar. To further verify migration of Bt‐Cry1Ac protein, Clostera anachoreta larvae, which are susceptible to Bt‐Cry1Ac protein, were fed leaves from the control graft (i.e., graft portion that originally did not contain Bt‐Cry1Ac protein). The results showed that Bt‐Cry1Ac protein was transported between rootstock and scion mainly through the phloem. Migration of Bt‐Cry1Ac protein in the grafted union was also evidenced in that the leaves of the control graft did have a lethal effect on C. anachoreta larvae in laboratory feeding experiments.     

Geographic variation in susceptibility of Chilo suppressalis (Lepidoptera: Pyralidae) to Bacillus thuringiensis toxins in China

Geographic variation in the susceptibility of the striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), in China to Bacillus thuringiensis (Bt) insecticidal crystal proteins Cry1Ac and Cry1Ab was studied to establish baseline information for comparing the future response of populations with increased exposure to Bt products. Rice is the major host of C. suppressalis, and Bt rice ma) be released in China in the near future. Twelve populations of the pest were collected from the major rice-growing regions of China. LC50 estimates were determined for all populations for Cry1Ac and for eight populations for Cry1Ab. The bioassay results indicated that the range of LC50 in neonate larvae to Cry1Ac and Cry1Ab was from approximately 15 to approximately 157 mg (AI)/L and approximately 2 to approximately 34 mg (AI)/L, respectively. LC50 values were lower for Cry1Ab than for Cry1Ac, and there was a significant positive correlation between the two toxins tested.