Bt Traits Research Articles

Effects of cultivation and return of Bacillus thuringiensis (Bt) maize on the diversity of the arbuscular mycorrhizal community in soils and roots of subsequently cultivated conventional maize

Cultivation of genetically modified maize (Zea mays L.) expressing the Cry1Ab protein from Bacillus thuringiensis (Bt) has increased worldwide since Bt maize was first commercialised. However, the cultivation and return of Bt maize has been shown to affect nontarget symbiotic soil-borne microbes such as arbuscular mycorrhizal fungi (AMF). In this study, we compared the diversity and composition of the AMF communities between two Bt maize plants (5422Bt1 [event Bt 11] and 5422CBCL [event MON 810]) and their conventional (non-Bt) isoline (5422) after cultivation for five seasons and return of straws by using molecular approaches, including terminal restriction fragment length polymorphism and DNA sequencing. Our data revealed that the diversities of AMF communities did not consistently differ significantly in soils and roots of subsequently planted conventional maize (SCM 5422) grown with Bt maize straw at three sampling stages (seedling, large bell, and maturity stages). DNA sequencing showed that typical AMF communities included Glomus, Paraglomus, Diversispora, Acaulospora, and Rhizophagus, of which Glomus was the most abundant. Funneliformis was detected only in bulk and rhizospheric soils and in roots of maize at the seedling stage. Rhizophagus was detected only in rhizospheric soils and only at the maturity stage. No significant effects related to the presence of Bt maize straw (5422Bt1 or 5422CBCL) were found by general linear analysis. However, plant growth stage had a greater influence on AMF diversity than Bt traits. In conclusion, cultivation of non-Bt maize on soils previously cultivated with Bt maize for five seasons had minor effects on AMF communities.

Larval survival and plant injury of Cry1F-susceptible, -resistant, and -heterozygous fall armyworm (Lepidoptera: Noctuidae) on non-Bt and Bt corn containing single or pyramided genes

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major target of transgenic corn, Zea mays L., expressing Bacillus thuringiensis (Bt) proteins in both North and South America. A highly Cry1F-resistant strain of S. frugiperda was established from a field collection in Puerto Rico in 2011. In this study, three greenhouse trials were conducted to evaluate larval survival and leaf injury of Cry1F-susceptible, -resistant, and -heterozygous genotypes of S. frugiperda on whole plants of five non-Bt and eight Bt corn hybrids. The Bt corn products included two single-gene Bt corn hybrids containing Herculex®I (Cry1F) and YieldGard® (Cry1Ab) traits and six pyramided Bt corn hybrids representing four traits: Genuity® VT Double Pro™, Genuity®VT Triple Pro™, Genuity® SmartStax™, and Agrisure® Viptera™ 3111. In each trial, neonates of S. frugiperda were placed into the plant whorls at vegetative plant stages (V6–V10). Larvae of the three insect genotypes on non-Bt corn hybrids survived well and caused serious plant injury. Cry1Ab corn was ineffective against all three insect genotypes. On Cry1F corn plants, resistant larvae survived on 72.9% plants after 12–15 d and caused a leaf injury rating (Davis' 1 to 9 scales) of 5.7 after 7 d and 7.6 after 12–15 d. Both the larval survivorship and leaf injury rates of the resistant larvae on Cry1F corn plants were not significantly different from those observed on non-Bt corn hybrids. In contrast, no live larvae and little or no leaf injury were observed on the Cry1F corn plants that were infested with susceptible or heterozygous genotypes, or on the pyramided Bt plants. The results demonstrated that the Cry1F-resistant S. frugiperda was highly resistant to whole plants of Cry1F corn and the resistance was recessive. Hybrids that contained one of the four pyramided Bt traits were effective for managing the Cry1F resistance in S. frugiperda.

The effect of nitrogen rate on transgenic corn Cry3Bb1 protein expression

Combining herbicide-resistant and Bacillus thuringiensis (Bt) traits in corn (Zea mays L.) hybrids may affect insect resistance management owing to volunteer corn. Some Bt toxins may be expressed at lower levels by nitrogen-deficient corn roots. Corn plants with sublethal levels of Bt expression could accelerate the evolution of Bt resistance in target insects. The present objective was to quantify the concentration of Bt (Cry3Bb1) in corn root tissue with varying tissue nitrogen concentrations. Expression of Cry3Bb1 toxin in root tissue was highly variable, but there were no differences in the overall concentration of Cry3Bb1 expressed between roots taken from Cry3Bb1-positive volunteer and hybrid corn plants. The nitrogen rate did affect Cry3Bb1 expression in the greenhouse, less nitrogen resulted in decreased Cry3Bb1 expression, yet this result was not documented in the field. A positive linear relationship of plant nitrogen status on Cry3Bb1 toxin expression was documented. Also, high variability in Cry3Bb1 expression is potentially problematic from an insect resistance management perspective. This variability could create a mosaic of toxin doses in the field, which does not fit into the high-dose refuge strategy and could alter predictions about the speed of evolution of resistance to Cry3Bb1 in western corn rootworm Diabrotica virgifera virgifera LeConte.

No effects of Bacillus thuringiensis maize on nontarget organisms in the field in southern Europe: a meta-analysis of 26 arthropod taxa

Maize with the insecticidal properties of the entomopathogenic bacterium Bacillus thuringiensis Berliner, known as Bt maize, has been sown in Europe since 1998. For several years, EU and Spanish regulations have required laboratory and field trials to assess risks of genetically modified crops for nontarget organisms prior to their authorization. Thirteen field trials were conducted in Spain to measure the effects of Bt maize on a broad range of arthropod taxa; no effects were found in accordance with most literature records. However, statistical analyses of single trials rarely have the statistical power to detect low effect sizes if they do not have a sufficient sample size. When sample size is low, meta-analysis may improve statistical power by combining several trials and assuming a common measure of effect size. Here we perform a meta-analysis of the results of 13 independent field trials conducted in Spain in which effects of single or stacked Bt traits on several arthropod taxa were measured with no significant results. Since the taxa included in each single trial were not the same for all trials, for the meta-analysis we selected only those taxa recorded in a minimum of six trials, resulting finally in 7, 7, and 12 taxa analyzed in visual counts, pitfall traps and yellow sticky traps, respectively. In comparison with single trial analysis, meta-analysis dramatically increased the detectability of treatment effects for most of the taxa regardless of the sampling technique; of the 26 taxa analyzed, only three showed poorer detectability in the meta-analysis than the best recorded in the 13 single trials. This finding reinforces the conclusion that Bt maize has no effect on the most common herbivore, predatory and parasitoid arthropods found in the maize ecosystems of southern Europe.

Implications of Bt Traits on Mycotoxin Contamination in Maize: Overview and Recent Experimental Results in Southern United States

Mycotoxin contamination levels in maize kernels are controlled by a complex set of factors including insect pressure, fungal inoculum potential, and environmental conditions that are difficult to predict. Methods are becoming available to control mycotoxin-producing fungi in preharvest crops, including Bt expression, biocontrol, and host plant resistance. Initial reports in the United States and other countries have associated Bt expression with reduced fumonisin, deoxynivalenol, and zearalenone contamination and, to a lesser extent, reduced aflatoxin contamination in harvested maize kernels. However, subsequent field results have been inconsistent, confirming that fumonisin contamination can be reduced by Bt expression, but the effect on aflatoxin is, at present, inconclusive. New maize hybrids have been introduced with increased spectra of insect control and higher levels of Bt expression that may provide important tools for mycotoxin reduction and increased yield due to reduced insect feeding, particularly if used together with biocontrol and host plant resistance.

The Impact of Volunteer Corn on Crop Yields and Insect Resistance Management Strategies

Volunteer corn (VC) has reemerged as a problematic weed in corn/soybean rotational cropping systems. This reemergence and increasing prevalence of volunteer corn has been correlated to an increased adoption of herbicide-resistant (HR) corn hybrids and the adoption of conservation tillage. Since the introduction of HR crops, control options, weed/crop competition, and other concerns (i.e., insect resistance management of Bt traits) have increased the amount of attention that volunteer corn is receiving. The objective of this review is to discuss what is known about VC prior to and after the introduction of HR crops, and to discuss new information about this important weed.

Corn Earworm (Lepidoptera: Noctuidae) in Northeastern Field Corn: Infestation Levels and the Value of Transgenic Hybrids

Corn earworm, Helicoverpa zea (Boddie), is a polyphagous noctuid pest of agricultural crops across the United States that is gaining attention as a pest of field corn. Before the introduction of transgenic insect-resistant hybrids, this pest was largely ignored in field corn, but now many Bacillus thuringiensis (Bt) corn hybrids have activity against corn earworm. However, the value of control in the northeastern United States is unclear because the risk posed by corn earworm to field corn has not been well characterized. To understand the threat from corn earworm and the value of Bt hybrids in field corn, we assessed corn earworm injury in Bt and non-Bt hybrids at 16 sites across four maturity zones throughout Pennsylvania in 2010, and 10 sites in 2011. We also used corn earworm captures from the PestWatch pheromone trapping network to relate moth activity to larval damage in field corn. Corn earworm damage was less than one kernel per ear at 21 of 26 sites over both years, and the percentage of ears damaged was generally < 15%, much lower than in the southern United States where damage can be up to 30 kernels per ear. At sites with the highest damage levels, Bt hybrids suppressed corn earworm damage relative to non-Bt hybrids, but we found no differences among Bt traits. Cumulative moth captures through July effectively predicted damage at the end of the season. Currently, the additional benefit of corn earworm control provided by Bt hybrids is typically less than US$4.00/ha in northeastern field corn.

Injury and Interplant Compensation for Southwestern Corn Borer (Lepidoptera: Crambidae) Infestations in Field Corn

Growers that plant Bacillus thuringiensis (Bt) Berliner corn (Zea mays L.) hybrids are required to plant non-Bt corn for resistance management. Refuge in a bag (RIB) is an emerging approach for resistance management where, for some hybrids having multiple Bt traits for a target species, the refuge is planted as a blend of Bt and non-Bt corn. Studies were conducted to evaluate how southwestern corn borer (Diatraea grandiosella Dyar), when infested at different densities and growth stages, affected the yield of infested, non-Bt plants and neighboring Bt plants. Infesting non-Bt corn plants with southwestern corn borer larvae caused significant injury. Both the number of larvae infested on plants and the timing of these infestations affected the number of kernels per ear, total kernel weight, and the weight of individual kernels. Infestation timing was more important than the number of larvae inoculated onto plants, with pretassel infestations causing more yield loss. There was little compensation by Bt plants that were adjacent to infested plants. Thus, the risk of yield loss from stalk tunneling larvae in a refuge in a bag scenario should be directly proportional to the percentage of non-Bt plants and the level of yield loss observed in these non-Bt plants. Because current refuge in a bag systems have five or 10% non-Bt corn plants within the seed unit, the likelihood of substantial yield losses from infestations of corn boring larvae is remote given our results, especially for infestations that occur after silking has begun.

Efficacy of Single and Dual Gene CottonGossypium hirsutumEvents on Neonate and Third Instar Fall Armyworm,Spodoptera frugiperdaDevelopment Based on Tissue and Meridic Diet Assays1

ABSTRACT We evaluated mortality and developmental parameters of fall armyworms, Spodoptera frugiperda (J. E. Smith), to the single Bacillus thuringiensis (Bt) cotton trait, Bollgard® and dual Bt cotton traits (Bollgard II® and WideStrike™) by using a cotton leaf-tissue assay and by incorporating lyophilized cotton tissue into a meridic diet. Bioassays were conducted for both neonate and 3rd instars. Leaf tissue bioassays indicated that Bollgard II® and WideStrike™ are highly effective against fall armyworm neonates by causing mortality and by retarding development parameters such as larval weight, pupal duration, and time to adulthood. Bollgard® was not significantly different from non-transgenic cotton in terms of mortality or feeding, with the exception of the non—Bt (PhytoGen 425RF), which had an inherent form of resistance that is not associated with a transgenic event. Third instars evaluated with lyophilized diet bioassays were not as affected by the Bt traits to the same degree as neonates; however...

Effectiveness of Transgenic Bt Cottons Against Noctuids in the Lower Rio Grande Valley of Texas

The comparative efficacy of Bacillus thuringiensis (Berliner) Bollgard, Bollgard II, WideStrike, and non-Bt expressing cotton, Gossypium hirsutum L., for control of the noctuid complex of bollworm, Helicoverpa zea (Boddie); fall armyworm, Spodoptera frugiperda (J. E. Smith); beet armyworm, Spodoptera exigua (Hübner); and cabbage looper, Trichoplusia ni (Hübner); was evaluated in the Lower Rio Grande Valley of Texas during 2004–2008. When noctuids were abundant, leaves or fruit were significantly less damaged and fewer live larvae were found on Bollgard II cotton compared with non-Bt cotton throughout the growing season. With few to moderate Lepidoptera, cotton with either of the two Bt traits had similar damage. One insecticide application to cotton with Bollgard, Bollgard II, WideStrike, or non-Bt traits resulted in significantly fewer bollworm and beet armyworm larvae and less damage on fruiting structures compared to nontreated cotton. Beet armyworm larval survival and damage to leaves on non-Bt cotton were 3.6-fold greater than on Bollgard II or WideStrike cotton and 1.5-fold greater than on cotton varieties with the Bollgard trait.

Evaluating the Performance of Transgenic Corn Producing Bacillus thuringiensis Toxins in South Carolina

Transgenic corn, Zea mays L., hybrids expressing insecticidal Cry proteins from Bacillus thuringiensis (Bt) were evaluated for control of insect pests from 2007 to 2009 in Florence and Blackville, South Carolina. Two planting dates were used in trials in 2009. Early- and mid-season pests and associated injury were consistently absent or at low numbers. Data analyses were limited to Helicoverpa zea (Boddie) injury and infestations in corn ears. Based on the number of kernels injured per ear, event MON810 significantly (P < 0.05) reduced injury compared with the non-Bt isoline in both trials in 2008 (average of 67% control), but reduced injury only in 2009 at the Florence location (64% control). Event TC1507 significantly reduced injury relative to its non-Bt isoline in trials in 2008 by an average of 51%. Based on one year of data at two locations in 2009, event MON89034 significantly reduced injury relative to the non-Bt isoline (average of 83% control), and was more effective than MON810 in the same trials. In 2009, the plots planted at the later date had significantly (P < 0.05) less injury on ears and kernels than the first planting date in Blackville; no differences were detected in Florence. Yield was not affected by Bt traits in any of the trials. The increased effectiveness of recent hybrids with the MON89034 event in controlling H. zea in corn ears may lead to increased planting of Bt corn in the southeastern United States, as prior events were not as effective in controlling this key pest.

A qualitative multi-attribute model for economic and ecological assessment of genetically modified crops

Genetically modified (GM) crops have become a real option in modern agriculture. They offer advantages for agricultural production, but they also raise concerns about their ecological and economic impacts. Decisions about GM crops are complex and call for decision support. This paper presents a qualitative multi-attribute model for the assessment of ecological and economic impacts at a farm-level of GM and non-GM maize crops. The model is applied for one agricultural season. This is an ex-ante model developed according to DEX methodology. In this model, cropping systems are defined by four groups of features: (1) crop sub-type, (2) regional and farm-level context, (3) crop protection and crop management strategies, and (4) expected characteristics of the harvest. The impact assessment of cropping systems is based on four groups of ecological and two groups of economic indicators: biodiversity, soil biodiversity, water quality, greenhouse gasses, variable costs and production value. The evaluation of cropping systems is governed by expert-defined rules. The paper describes the structure and components of the model, and presents three practical applications of the model, assessing both hypothetical and real-life cropping systems. In an overall assessment of the ecological and economic outcomes the model ranked cropping systems in the order: organically managed > GM systems including Bt and HT traits > conventionally managed maize. The paper discusses contributions of the model to decision-making practice and highlights methodological lessons learned during its development.

Corn Expressing Cry1Ab or Cry1F endotoxin for Fall Armyworm and Corn Earworm (Lepidoptera: Noctuidae) management in Field Corn for Grain Production

Fall armyworm, Spodoptera frugiperda (J. E. Smith), and corn earworm, Helicoverpa zea (Boddie), perennially cause leaf and ear damage to corn in the southeastern United States. Transgenic hybrids expressing the Cry1Ab (MON810 event) or Cry 1F (TC1507 event) insecticidal endotoxin from Bacillus thuringiensis (Bt) were evaluated for management of fall armyworm and corn earworm in central Georgia during 2006 and 2007. Corn was planted at the recommended time in mid-Apr and in late Jun to simulate a double-crop corn planting. Both Bt events reduced whorl infestation and damage by fall armyworm, but TC1507 provided greater protection from whorl injury than MON 810 under severe fall armyworm infestations. Hybrids with the MON810 event usually had less ear infestation by corn earworm than susceptible hybrids, whereas the TC1507 event usually did not reduce ear infestations. Nevertheless, both events prevented ear damage, but there was no consistent difference between the two Bt traits in preventing ear damage. Bt traits did not affect grain yield in either year during the first planting when fall armyworm infestations were low. Both events prevented significant yield loss during the second planting in 2006 when whorl infestation levels exceeded 50% in susceptible hybrids. Because of the greater activity in preventing whorl damage by fall armyworm, the TC1507 event would be useful in mitigating the risk of severe lepidopteran damage to later plantings of field corn for grain production in the southeastern U.S.

Insect resistance management for Syngenta’s VipCot™ transgenic cotton

Syngenta is seeking commercial registration for VipCot™ cotton, a pyramided transgenic cotton trait that expresses two insecticidal proteins derived from Bacillus thuringiensis Vip3A and Cry1Ab. Both proteins are highly effective against two key cotton pests, Helicoverpa zea cotton bollworm; and Heliothis virescens, tobacco budworm. To investigate the role of VipCot™ cotton in delaying the development of resistance in these pests to transgenic Bt traits, Syngenta has performed studies to determine the dose of proteins expressed in VipCot™ and evaluate the potential for cross-resistance between the component proteins. Following United States Environmental Protection Agency (US EPA) high dose methods 1 and 4, VipCot™ was shown to express a high dose of proteins for H. zea and H. virescens. VipCot™ was also confirmed to express a high dose of proteins for H. zea through US EPA Method 5. Additionally, all the data collected to date verify a lack of cross-resistance between Vip3A and Cry proteins. These two key pieces of information indicate that VipCot™ cotton should be very durable under the currently mandated high dose plus refuge insect resistance management strategy.