转Bt基因玉米的生态安全性研究进展

随着转基因作物的应用和推广 ,转 Bt基因作物释放后对生态环境及其它方面产生的潜在影响越来越受到重视。分别从生物活性杀虫晶体蛋白在土壤中的残留特性、杀虫晶体蛋白对土壤中非目标生物的影响、转 Bt基因玉米植株体成分的变化、转Bt基因玉米花粉中杀虫晶体蛋白的表达特性及其在田间和马力筋叶片上的散积状况、花粉中表达的杀虫晶体蛋白对君主斑蝶的毒性、君主斑蝶幼虫暴露在 Bt花粉中的概率及综合风险评价估算等方面对转 Bt基因玉米产生的杀虫晶体蛋白与土壤生态环境的相互作用、花粉对非目标生物影响的研究现状进行了综述。通过对转 Bt基因作物生态安全性的科学评价和广泛宣传 ,以确保生物技术的健康发展。     

Cross-Resistance between Cry1 Proteins in Fall Armyworm (Spodoptera frugiperda) May Affect the Durability of Current Pyramided Bt Maize Hybrids in Brazil

Genetically modified plants expressing insecticidal proteins from Bacillus thuringiensis (Bt) offer valuable options for managing insect pests with considerable environmental and economic benefits. Despite the benefits provided by Bt crops, the continuous expression of these insecticidal proteins imposes strong selection for resistance in target pest populations. Bt maize (Zea mays) hybrids have been successful in controlling fall armyworm (Spodoptera frugiperda), the main maize pest in Brazil since 2008; however, field-evolved resistance to the protein Cry1F has recently been reported. Therefore it is important to assess the possibility of cross-resistance between Cry1F and other Cry proteins expressed in Bt maize hybrids. In this study, an F₂ screen followed by subsequent selection on MON 89034 maize was used to select an S. frugiperda strain (RR) able to survive on the Bt maize event MON 89034, which expresses the Cry1A.105 and Cry2Ab2 proteins. Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found. The RR strain showed high levels of resistance to Cry1F, which apparently also conferred high levels of cross resistance to Cry1A.105 and Cry1Ab, but had only low-level (10-fold) resistance to Cry2Ab2. Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively. Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil. Nevertheless, the occurrence of Cry1F resistance in S. frugiperda across Brazil, and the cross-resistance to Cry1Ab and Cry1A.105, indicates that current Cry1-based maize hybrids face a challenge in managing S. frugiperda in Brazil and highlights the importance of effective insect resistance management for these technologies.     

A review on comparative data concerning <Emphasis Type="Italic">Fusarium</Emphasis> mycotoxins in Bt maize and non-Bt isogenic maize

The European corn borer reportedly promotes the infection of maize by Fusarium spp. Stalk and ear rots caused by Fusarium spp. are often related to mycotoxin accumulation in maize kernels. As a result, food and animal feed from maize are more severely contaminated with Fusarium mycotoxins: e.g. fumonisins (FUM), deoxynivalenol (DON) and zearalenone (ZEA). Bt maize is primarily an important potential tool for insect pest protection, both in the European Union and in other countries. Bt maize carrying the Bt genes is highly resistant to European corn borer larval feeding due to Bt toxin (δ toxin) production. Effective measures to combat pests therefore often have a positive side-effect in that they also reduce mycotoxin levels. Comparative analysis was used to the evaluation of the studies dealing with the reduction of Fusarium mycotoxins in Bt maize. Nineteen out of 23 studies on Bt maize came to the conclusion that Bt maize is less contaminated with mycotoxins (FUM, DON, ZEA) than the conventional control variety in each case.     

The effect of Bt maize on Sesamia calamistis in South Africa

Bt maize, Zea mays L. (Poaceae) expressing Cry 1Ab insecticidal proteins was introduced for control of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) in South Africa after its development for control of crambid borers in North America. In the light of the reportedly lower toxicity of Bt maize to certain Noctuidae borers, the effect of Bt maize was evaluated on Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae). The characteristic larval behaviour of S. calamistis may result in reduced exposure to Bt toxin and subsequent high levels of survival. Larvae do not feed on plant whorls like other borer species but penetrate stems directly from behind leaf sheaths where eggs are laid. Greenhouse and laboratory bioassays were done with three Bt maize hybrids and their iso‐hybrids. ‘Whole plant methods’ were used and potted plants artificially infested with eggs or larvae and survival recorded over time. Larval survival was also determined on different plant parts (whorls, stems, tillers, and ears) over time. Bt maize was shown to be highly toxic to S. calamistis. No larvae survived longer than 12–18 days on Bt maize plants in any of the experiments. Adults did not differentiate between Bt and non‐Bt plants in oviposition choice experiments. Sesamia calamistis is polyphagous and occurs in mixed populations with other borer species with which it shares many parasitoid species in Africa. The ecological impact of local extinction of S. calamistis caused by this highly effective transgenic event is therefore not expected to be great.     

Farm‐scale evaluation of the impact of Cry1Ab Bt maize on canopy nontarget arthropods: a 3‐year study

The cultivation of Cry1Ab‐expressing genetically modified MON810 (Bt maize) has led to public concern in Europe, regarding its impact on nontarget arthropods (NTAs). We have assessed the potential effects of DKC 6451 YG (MON810) maize on canopy NTAs in a farm‐scale study performed in Central Spain during 3 years. The study focused on hemipteran herbivores (leafhoppers and planthoppers) and hymenopteran parasitic wasps (mymarids) collected by yellow sticky traps, which accounted for 72% of the total number of insects studied. The dynamics and abundance of these groups varied among years, but no significant differences were found between Bt and non‐Bt maize, indicating that Bt maize had no negative effect on these taxa. Nonetheless, the Cry1Ab toxin was detected in 2 different arthropods collected from Bt maize foliage, the cicadellids Zyginidia scutellaris and Empoasca spp. A retrospective power analysis on the arthropod abundance data for our field trials has determined that Z. scutellaris and the family Mymaridae have high capacity to detect differences between the Bt maize and its isogenic counterpart. The use of these canopy NTAs as surrogates for assessing environmental impacts of Bt maize is discussed.     

Bt maize can provide non-chemical pest control and enhance food safety in China

China is the world's second-largest maize producer and consumer. In recent years, the invasive fall armyworm Spodoptera frugiperda (J.E. Smith) has adversely affected maize productivity and compromised food security. To mitigate pest-inflicted food shortages, China's Government issued biosafety certificates for two genetically modified (GM) Bt maize hybrids, Bt-Cry1Ab DBN9936 and Bt-Cry1Ab/Cry2Aj Ruifeng 125, in 2019. Here, we quantitatively assess the impact of both Bt maize hybrids on pest feeding damage, crop yield and food safety throughout China's maize belt. Without a need to resort to synthetic insecticides, Bt maize could mitigate lepidopteran pest pressure by 61.9–97.3%, avoid yield loss by 16.4–21.3% (range −11.9–99.2%) and lower mycotoxin contamination by 85.5–95.5% as compared to the prevailing non-Bt hybrids. Yield loss avoidance varied considerably between experimental sites and years, as mediated by on-site infestation pressure and pest identity. For either seed mixtures or block refuge arrangements, pest pressure was kept below established thresholds at 90% Bt maize coverage in Yunnan (where S. frugiperda was the dominant species) and 70% Bt maize coverage in other sites dominated by Helicoverpa armigera (Hübner) and Ostrinia furnacalis (Guenée). Drawing on experiences from other crop/pest systems, Bt maize in se can provide area-wide pest management and thus, contribute to a progressive phase-down of chemical pesticide use. Hence, when consciously paired with agroecological and biodiversity-based measures, GM insecticidal crops can ensure food and nutrition security, contribute to the sustainable intensification of China's agriculture and reduce food systems' environmental footprint.     

High susceptibility of Bt maize to aphids enhances the performance of parasitoids of lepidopteran pests

Concerns about possible undesired environmental effects of transgenic crops have prompted numerous evaluations of such crops. So-called Bt crops receive particular attention because they carry bacteria-derived genes coding for insecticidal proteins that might negatively affect non-target arthropods. Here we show a remarkable positive effect of Bt maize on the performance of the corn leaf aphid Rhopalosiphum maidis, which in turn enhanced the performance of parasitic wasps that feed on aphid honeydew. Within five out of six pairs that were evaluated, transgenic maize lines were significantly more susceptible to aphids than their near-isogenic equivalents, with the remaining pair being equally susceptible. The aphids feed from the phloem sieve element content and analyses of this sap in selected maize lines revealed marginally, but significantly higher amino acid levels in Bt maize, which might partially explain the observed increased aphid performance. Larger colony densities of aphids on Bt plants resulted in an increased production of honeydew that can be used as food by beneficial insects. Indeed, Cotesia marginiventris, a parasitoid of lepidopteran pests, lived longer and parasitized more pest caterpillars in the presence of aphid-infested Bt maize than in the presence of aphid-infested isogenic maize. Hence, depending on aphid pest thresholds, the observed increased susceptibility of Bt maize to aphids may be either a welcome or an undesirable side effect.     

High-throughput sequence-based analysis of the intestinal microbiota of weanling pigs fed genetically modified MON810 maize expressing Bacillus thuringiensis Cry1Ab (Bt maize) for 31 days

The objective of this study was to investigate if feeding genetically modified (GM) MON810 maize expressing the Bacillus thuringiensis insecticidal protein (Bt maize) had any effects on the porcine intestinal microbiota. Eighteen pigs were weaned at ~28 days and, following a 6-day acclimatization period, were assigned to diets containing either GM (Bt MON810) maize or non-GM isogenic parent line maize for 31 days (n = 9/treatment). Effects on the porcine intestinal microbiota were assessed through culture-dependent and -independent approaches. Fecal, cecal, and ileal counts of total anaerobes, Enterobacteriaceae, and Lactobacillus were not significantly different between pigs fed the isogenic or Bt maize-based diets. Furthermore, high-throughput 16S rRNA gene sequencing revealed few differences in the compositions of the cecal microbiotas. The only differences were that pigs fed the Bt maize diet had higher cecal abundance of Enterococcaceae (0.06 versus 0%; P < 0.05), Erysipelotrichaceae (1.28 versus 1.17%; P < 0.05), and Bifidobacterium (0.04 versus 0%; P < 0.05) and lower abundance of Blautia (0.23 versus 0.40%; P < 0.05) than pigs fed the isogenic maize diet. A lower enzyme-resistant starch content in the Bt maize, which is most likely a result of normal variation and not due to the genetic modification, may account for some of the differences observed within the cecal microbiotas. These results indicate that Bt maize is well tolerated by the porcine intestinal microbiota and provide additional data for safety assessment of Bt maize. Furthermore, these data can potentially be extrapolated to humans, considering the suitability of pigs as a human model.     

Molecular,biochemical and bioassay based evidence of lower allelopathic potential in genetically modified rice

This study examines allelopathic potential of genetically modified rice. The experiment was conducted on two isogenic lines Bacillus thuringiensis (Bt) and non-Bacillus thuringiensis (non-Bt). Both isogenic lines have same allelopathic ability before insect feeding and after limited insect feeding (Spodoptera litura) non-Bt rice genotype demonstrates more allelopathic potential. The S. litura cannot feed Bt rice genotype. The role of shoot herbivory in allelopathic induction is further supported when Bt plants also exhibited higher allelopathic potential after insect regurgitant application to the damaged leaves. Allelopathic potential was assessed through several methods after treatments of mechanical damage, insect feeding and insect regurgitant application to damaged rice leaves. Rhizosphere soil and leaf leachates of non-Bt rice cultivar exhibited higher allelopathic potential on lettuce and barnyard grass after herbivore feeding. Enzyme activities (PAL and C4H) responsible for biosynthesis of phenolic compounds and their concentration were significantly higher in non-Bt plant after herbivore feeding and attain the same level in Bt plants after insect regurgitant application to damaged leaves. Similarly, genes (OsPAL and OsCYC1) responsible for biosynthesis of allelopathic compounds showed high expression in non-Bt plants after herbivore feeding. Our results indicate that herbivore feeding enhance rice allelopathic potential and no insect feeding as incase of Bt plants may reduce allelopathic potential of genetically modified rice.     

Preference of Neoseiulus californicus (Acari: Phytoseiidae) for volatiles of Bt maize induced by multiple herbivory

Plant indirect induced defenses against herbivores are characterized by the production of plant volatiles that to attract natural enemies. The objective of this study was to evaluate whether the attack of the two-spotted spider mite Tetranychus urticae or the multiple herbivory of T. urticae together with the fall armyworm Spodoptera frugiperda are able to elicit indirect induced defense in conventional and Bt maize plants. The experiment was carried out in the laboratory using Y-tube olfactometer, evaluating the predatory mite Neoseiulus californicus olfactory preference for plant volatiles. The treatments involved: Clean Conventional Plant; Conventional Plant Infested with T. urticae; Clean Bt Plant; Bt Plant Infested with T. urticae; Conventional Plant Infested with T. urticae + fall armyworm; Bt Plant Infested with T. urticae + fall armyworm. For the chemical analyzes the Trace GC Ultra gas chromatograph was used, paired with the Polaris Q mass spectrometer, GCMS system. Neoseiulus californicus was also unable to distinguish between volatiles from both conventional and Bt infested maize plants. Moreover, there was no discrimination of the predator mite between plants under single and multiple infestations, both in conventional and Bt maize. When comparing conventional and Bt plants, both with multiple infestation, the predator mite N. californicus had no preference among these sources of odors. However, there was observed chemical changes of the volatiles among the groups of plants studied. Thus, it is suggested that the groups of plants under study have chemical modifications, but they are not able to attract N. californicus. In addition, Bt plants response was similar to conventional plants on attracting N. californicus.     

Effects of Bt maize expressing Cry1Ab and Bt spray on Spodoptera littoralis

Various studies have been conducted to assess the damage caused by secondary lepidopteran pests to transgenic Bt maize expressing Cry1Ab. However, to date little is known on the effects of transgenic maize on Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), a polyphagous herbivore which is considered a pest in Mediterranean maize growing areas. Here we present results on the effects of Bt maize (Bt‐11) and Bt spray (Dipel) on the various life stage parameters of this herbivore. We further assess the expression of Cry1Ab in different leaves and leaf parts in maize at a given plant growth stage, and determine whether the feeding damage of 3rd instar S. littoralis is influenced by Bt toxin expression. Contrary to previous literature reporting that S. littoralis is not sensitive to Bt Cry1Ab toxin, our results show that insects fed on either transgenic or Bt sprayed plants were negatively affected. Young S. littoralis larvae (1st and 2nd instars) were found to be the most sensitive to the Bt toxin. This was represented by a higher mortality and a slower developmental time of larvae maintained on transgenic or sprayed plants when compared to insects maintained on control plants. Moreover, Bt maize had a stronger and prolonged detrimental effect on insects when compared to Bt spray in maize. This was revealed by the fact that insects maintained on transgenic plants from 3rd instar to pupation took longer to reach adult emergence compared to insects that were maintained on sprayed plants. This was likely due to the continuous exposure of insects to the toxin when kept on transgenic maize. ELISA results showed a variation in the amount of Bt toxin among different leaf sections in transgenic maize at a given plant growth stage. These differences in Bt toxin were primarily found in the youngest leaf of growing plants. Although the lowest amounts of Bt toxin were detected in the growing leaf section of young leaves, this difference did not appear to influence the feeding behavior of 3rd instar S. littoralis.     

Evaluation of soil‐applied insecticides with Bt maize for managing corn rootworm larval injury

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is considered one of the most significant insect pests of maize in North America. Larvae of other secondary subterranean pests such as grape colaspis, Colaspis brunnea (F.), and Japanese beetle, Popillia japonica Newman, can also injure maize seedlings and cause yield loss. In the past decade, maize hybrids containing Bt proteins have been used to manage the western corn rootworm; additionally, seeds are commonly treated with a neonicotinoid and fungicide combination to control secondary pests. Recently, soil‐applied insecticides have been used in conjunction with rootworm Bt hybrids (and seed‐applied insecticides) in areas with perceived risk for increased rootworm larval or secondary pest damage. We conducted a series of trials from 2009 to 2011 that examined multiple rootworm Bt hybrids and their near‐isolines, along with two soil‐applied insecticides, to determine whether the Bt plus insecticide combination resulted in an increased level of efficacy or yield. We also sampled for Japanese beetle and grape colaspis larvae to determine their potential for reducing yield. Densities of secondary pests in our trials were low and likely had no effect on maize yield. The addition of a soil‐applied insecticide to rootworm Bt hybrids improved efficacy only once across 17 location‐years, when overall corn rootworm injury was highest; an improvement in yield was never observed. Our results suggest that the use of a soil‐applied insecticide with a rootworm Bt hybrid should only be considered in scenarios with potentially significant rootworm larval populations. However, potential negative consequences related to trait durability when soil insecticides are used with rootworm Bt maize should be considered.     

Biodetrimental effects of the Corn hybrids,Neemazal-T/S and Chlorphan 48% on the pink corn borer Sesamia cretica Led.

The aim of this study was to investigate influence of transgenic and commercial corn hybrids on the behaviour and feeding activity of the pink corn borer (Sesamia cretica Led.). Food consumption was different according to feeding period and hybrids. The feeding ratio of S. cretica on maize hybrids was significantly different between transgenic and commercial hybrids. It appears from the results of this experiment that the antifeeeding activity of transgenic hybrids had greater effect than commercial hybrids one. Thus, it is apparent from these results that transgenic maize was unsuitable because larvae were dead, but the other commercial hybrids were preferable. It can be concluded from the data that the feeding on different maize hybrids had different effects on certain biological aspects of pink corn borer. The impact of untreated Bt. Corn; 0.5% water emulsion of Neem-Azal-T/S and 0.005% water emulsion of Chlorpyrifos insecticides on the behaviour and feeding activity of the pink corn borer S. cretica has been studied. The data showed that larvae stopped feeding from the time when it was fed on untreated Bt. corn or/and non Bt. Corn treated with NeemAzal-T/S 0.5%. The results indicated that Bt. corn, NeemAzal-T/S 0.5% and Chlorphan 48% (0.005%) possessed the toxic effect on pink corn borer S. cretica. According to results, it could be stated that the tested compounds can play an important role in controlling the pink corn borer.     

Assessing the Effects of Bt Maize on the Predatory Mite Neoseiulus cucumeris

The investigation of Neoseiulus cucumeris in the context of the ecological risk assessment of insect resistant transgenic plants is of particular interest as this omnivorous predatory mite species is commercially available and considered important for biological control. In a multitrophic feeding experiment we assessed the impact of Bt maize on the performance of N. cucumeris when offered spider mites (Tetranychus urticae) reared on Bt (Bt11, Syngenta) or non-Bt maize (near isogenic line) and Bt or non-Bt maize pollen as a food source. Various parameters including mortality, development time, oviposition rate were measured. Spider mites were used as a prey for N. cucumeris, since these herbivores are known to contain similar levels of Cry1Ab toxin, when reared on Bt maize, as those found in the transgenic leaf material. In contrast, toxin levels in pollen of this transgenic cultivar are very low. No differences in any of the parameters were found when N. cucumeris was fed with spider mites reared on Bt and non-Bt maize. Pollen was shown to be a less suitable food source for this predator as compared to spider mites. Moreover, subtle effects on female N. cucumeris (9% longer development time and 17% reduced fecundity) were measured when fed with pollen originating from Bt maize as compared to non-Bt maize pollen. Our findings indicate that the predatory mite N. cucumeris is not sensitive to the Cry1Ab toxin as no effects could be detected when offered Bt-containing spider mites, and that the effects found when fed with Bt maize pollen can be assigned to differences in nutritional quality of Bt and non-Bt maize pollen. The significance of these findings is discussed with regard to the ecological relevance for risk assessment of transgenic plants.     

A Challenge for the Seed Mixture Refuge Strategy in Bt Maize: Impact of Cross-Pollination on an Ear-Feeding Pest,Corn Earworm

To counter the threat of insect resistance, Bacillus thuringiensis (Bt) maize growers in the U.S. are required to plant structured non-Bt maize refuges. Concerns with refuge compliance led to the introduction of seed mixtures, also called RIB (refuge-in-the-bag), as an alternative approach for implementing refuge for Bt maize products in the U.S. Maize Belt. A major concern in RIB is cross-pollination of maize hybrids that can cause Bt proteins to be present in refuge maize kernels and negatively affect refuge insects. Here we show that a mixed planting of 5% nonBt and 95% Bt maize containing the SmartStax traits expressing Cry1A.105, Cry2Ab2 and Cry1F did not provide an effective refuge for an important above-ground ear-feeding pest, the corn earworm, Helicoverpa zea (Boddie). Cross-pollination in RIB caused a majority (>90%) of refuge kernels to express ≥ one Bt protein. The contamination of Bt proteins in the refuge ears reduced neonate-to-adult survivorship of H. zea to only 4.6%, a reduction of 88.1% relative to larvae feeding on ears of pure non-Bt maize plantings. In addition, the limited survivors on refuge ears had lower pupal mass and took longer to develop to adults.     

Presence of Cry1Ab in the Bt maize – aphid (Rhopalosiphum maidis) – ladybeetle (Propylea japonica) system has no adverse effects on insect biological parameters

Transgenic Bacillus thuringiensis Berliner (Bt) crops receive particular attention because they carry genes encoding insecticidal proteins that might negatively affect non‐target arthropods. Here, laboratory experiments were conducted to evaluate the impact of Cry1Ab‐expressing transgenic maize [5422Bt1 (event Bt11) and 5422CBCL (MON810)] on the biological parameters of two non‐target arthropods, the aphid Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae) and its predator the ladybeetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae). In a long‐term assay (three generations), no significant differences were found between R. maidis fed Bt maize and those fed a near‐isogenic line (5422) when individual parameters were compared, including nymph development time, adult longevity, aphid spawning period, and fecundity. No negative effects were detected throughout the life cycle of P. japonica in aphids’ feeding amount, development (nymphs, pupae, adults, and progeny eggs), fecundity, or egg hatching when they preyed on Bt maize‐fed aphids compared with non‐Bt maize treatments. A tritrophic assay revealed that Cry1Ab was highly diluted through the food chain (Bt maize leaves, R. maidis, and P. japonica), as detected by an enzyme‐linked immunosorbent assay (ELISA). In conclusion, although Cry1Ab concentrations in maize leaves increased as the plants developed, Cry1Ab levels were significantly reduced in the aphid R. maidis, and no traces of Cry1Ab were detected in P. japonica preying on Bt maize‐fed aphids. The two hybrids of Bt maize expressing Cry1Ab had no negative effects on the measured biological parameters of the aphid R. maidis or its predator, the ladybeetle P. japonica.     

The Cry1Ab Protein Has Minor Effects on the Arbuscular Mycorrhizal Fungal Communities after Five Seasons of Continuous Bt Maize Cultivation

The cultivation of genetically modified plants (GMP) has raised concerns regarding the plants’ ecological safety. A greenhouse experiment was conducted to assess the impact of five seasons of continuous Bt (Bacillus thuringiensis) maize cultivation on the colonisation and community structure of the non-target organisms arbuscular mycorrhizal fungi (AMF) in the maize roots, bulk soils and rhizospheric soils using the terminal restriction fragment length polymorphism (T-RFLP) analysis of the 28S ribosomal DNA and sequencing methods. AMF colonisation was significantly higher in the two Bt maize lines that express Cry1Ab, 5422Bt1 (event Bt11) and 5422CBCL (MON810) than in the non-Bt isoline 5422. No significant differences were observed in the diversity of the AMF community between the roots, bulk soils and rhizospheric soils of the Bt and non-Bt maize cultivars. The AMF genus Glomus was dominant in most of the samples, as detected by DNA sequencing. A clustering analysis based on the DNA sequence data suggested that the sample types (i.e., the samples from the roots, bulk soils or rhizospheric soils) might have greater influence on the AMF community phylotypes than the maize cultivars. This study indicated that the Cry1Ab protein has minor effects on the AMF communities after five seasons of continuous Bt maize cultivation.     

Quantitative analysis of CryIA(b) expression in Bt maize plants,tissues, and silage and stability of expression over successive generations

The range and stability of expression of the transgenic CryIA(b) protein was examined in Ciba Seeds Bt maize plants derived from Event 176. Specifically, CryIA(b) levels were determined for: (1) various plant tissues and developmental stages in three maize lines from 1993 field tests; (2) pollen and leaves from plants representing four backcross generations of two genotypes; (3) leaves of 6 precommercial hybrids; and (4) silage from one Bt maize hybrid. Significant levels were found only in pollen and leaves. Genetic background did not greatly impact the level seen in either tissue. CryIA(b) expression in maize plants derived from transformation Event 176 was stable over at least four successive generations. On a per acre basis, the highest amount of CryIA(b) protein (estimated to be 2-4 g CryIA(b) protein/acre) was found to occur at anthesis, consistent with the stage at which maximum plant vegetative biomass is reached. CryIA(b) was not detected in silage prepared from CryIA(b)-expression plants. The maize-expressed CryIA(b) protein was found to have the expected size and to be immunoreactive with antibodies prepared against crystals from Bacillus thuringiensis subsp. kurstaki.     

Field Evaluation of Arbuscular Mycorrhizal Fungal Colonization in Bacillus thuringiensis Toxin-Expressing (Bt) and Non-Bt Maize

The cultivation of genetically engineered Bacillus thuringiensis toxin-expressing (Bt) maize continues to increase worldwide, yet the effects of Bt crops on arbuscular mycorrhizal fungi (AMF) in soil are poorly understood. In this field experiment, we investigated the impact of seven different genotypes of Bt maize and five corresponding non-Bt parental cultivars on AMF and evaluated plant growth responses at three different physiological time points. Plants were harvested 60 days (active growth), 90 days (tasseling and starting to produce ears), and 130 days (maturity) after sowing, and data on plant growth responses and percent AMF colonization of roots at each harvest were collected. Spore abundance and diversity were also evaluated at the beginning and end of the field season to determine whether the cultivation of Bt maize had a negative effect on AMF propagules in the soil. Plant growth and AMF colonization did not differ between Bt and non-Bt maize at any harvest period, but AMF colonization was positively correlated with leaf chlorophyll content at the 130-day harvest. Cultivation of Bt maize had no effect on spore abundance and diversity in Bt versus non-Bt plots over one field season. Plot had the most significant effect on total spore counts, indicating spatial heterogeneity in the field. Although previous greenhouse studies demonstrated that AMF colonization was lower in some Bt maize lines, our field study did not yield the same results, suggesting that the cultivation of Bt maize may not have an impact on AMF in the soil ecosystem under field conditions.     

Bt Crops Producing Cry1Ac,Cry2Ab and Cry1F Do Not Harm the Green Lacewing,Chrysoperla rufilabris

The biological control function provided by natural enemies is regarded as a protection goal that should not be harmed by the application of any new pest management tool. Plants producing Cry proteins from the bacterium, Bacillus thuringiensis (Bt), have become a major tactic for controlling pest Lepidoptera on cotton and maize and risk assessment studies are needed to ensure they do not harm important natural enemies. However, using Cry protein susceptible hosts as prey often compromises such studies. To avoid this problem we utilized pest Lepidoptera, cabbage looper (Trichoplusia ni) and fall armyworm (Spodoptera frugiperda), that were resistant to Cry1Ac produced in Bt broccoli (T. ni), Cry1Ac/Cry2Ab produced in Bt cotton (T. ni), and Cry1F produced in Bt maize (S. frugiperda). Larvae of these species were fed Bt plants or non-Bt plants and then exposed to predaceous larvae of the green lacewing Chrysoperla rufilabris. Fitness parameters (larval survival, development time, fecundity and egg hatch) of C. rufilabris were assessed over two generations. There were no differences in any of the fitness parameters regardless if C. rufilabris consumed prey (T. ni or S. frugiperda) that had consumed Bt or non-Bt plants. Additional studies confirmed that the prey contained bioactive Cry proteins when they were consumed by the predator. These studies confirm that Cry1Ac, Cry2Ab and Cry1F do not pose a hazard to the important predator C. rufilabris. This study also demonstrates the power of using resistant hosts when assessing the risk of genetically modified plants on non-target organisms.