Bt Maize Hybrids Research Articles

Assessing the Efficacy of Bacillus thuringiensis (Bt) Pyramided Proteins Cry1F, Cry1A.105, Cry2Ab2, and Vip3Aa20 Expressed in Bt Maize Against Lepidopteran Pests in Brazil.

Field studies across four states in maize-producing areas of Brazil were conducted to characterize the efficacy of a new pyramided Bacillus thuringiensis (Bt) Berliner technology in maize, Zea mays L., and compare it to existing single and pyramided commercial Bt technologies, to control Helicoverpa zea Boddie (Lepidoptera: Noctuidae), Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), and Diatraea saccharalis F. (Lepidoptera: Crambidae). Bt maize expressing Vip3Aa20 protein and pyramided Bt maize expressing proteins Cry1F + Cry1A.105 + Cry2Ab2 + Vip3Aa20 provided excellent protection against kernel feeding by H. zea compared to Bt technologies expressing only Cry1F or Cry1A.105 + Cry2Ab2. Bt maize expressing Cry1F, Cry1A.105 + Cry2Ab2, Cry1F + Cry1A.105 + Cry2Ab2, and Cry1F + Cry1A.105 + Cry2Ab2 + Vip3Aa20 resulted in less than 5% of plants injured by E. lignosellus, significantly less than Bt maize expressing only Vip3Aa20 and a non-Bt maize iso-hybrid with and without a thiamethoxam seed treatment. The highest protection against plant cutting injury caused by A. ipsilon was observed in the pyramid Bt maize technology expressing Cry1F + Cry1A.105 + Cry2Ab2 + Vip3Aa20. However, it did not differ statistically from the Bt maize expressing Vip3Aa20, Cry1F, or Cry1F + Cry1A.105 + Cry2Ab2. All Bt maize hybrids evaluated in our study were highly effective in reducing tunneling injury caused by D. saccharalis. These results show that a new maize technology expressing pyramided Bt proteins Cry1F + Cry1A.105 + Cry2Ab2 + Vip3Aa20 offers a higher level of protection from feeding by the above lepidopteran pest complex compared to maize with a single Bt protein or double pyramided Bt proteins.

Management of Field-Evolved Resistance to Bt Maize in Argentina: A Multi-Institutional Approach

Evolution of resistance to control measures in insect populations is a natural process, and management practices are intended to delay or mitigate resistance when it occurs. During the 2012/13 season the first reports of unexpected damage by Diatraea saccharalis on some Bt maize hybrids occurred in the northeast of San Luis province, Argentina. The affected Bt technologies were Herculex I® (HX-TC1507) and VT3PRO® (MON 89034 × MON 88017*). Event TC1507 expresses Cry1F and event MON 89034 expresses Cry1A.105 and Cry2Ab2, whichr are all Bt proteins with activity against the lepidopterans D. saccharalis and Spodoptera frugiperda (MON 88017 expresses the protein Cry3Bb1 for control of coleopteran insects and the enzyme CP4EPSPS for glyphosate tolerance). The affected area is an isolated region surrounded by sierra systems to the northeast and west, with a hot semi-arid climate, long frost-free period, warm winters, hot dry summers, and woody shrubs as native flora. To manage and mitigate the development of resistance, joint actions were taken by the industry, growers and Governmental Agencies. Hybrids expressing Vip3A protein (event MIR162) and/or Cry1Ab protein (events MON 810 and Bt11) as single or stacked events are used in early plantings to control the first generations of D. saccharalis, and in later plantings date's technologies with good control of S. frugiperda. A commitment was made to plant the refuge, and pest damage is monitored. As a result, maize production in the area is sustainable and profitable with yields above the average.

Fusarium graminearum Mycotoxins in Maize Associated With Striacosta albicosta (Lepidoptera: Noctuidae) Injury

Western bean cutworm, Striacosta albicosta (Smith; Lepidoptera: Noctuidae) has become a key pest of maize, Zea mays (L.), in Ontario, Canada which is challenging to control due to its lack of susceptibility to most Bt-maize events. Injury by S. albicosta may exacerbate Fusarium graminearum (Schwabe; Hypocreales: Nectriaceae) infection through provision of entry points on the ear. The objectives of this study were to: investigate the relationship between injury by S. albicosta and deoxynivalenol (DON) accumulation; evaluate non-Bt and Bt-maize hybrids, with and without insecticide and fungicide application; and determine optimal insecticide-fungicide application timing for reducing S. albicosta injury and DON accumulation. The incidence of injury by S. albicosta and ear rot severity were found to increase DON concentrations under favorable environmental conditions for F. graminearum infection. Incidence of S. albicosta injury was more important than severity of injury for DON accumulation which may be due to larval consumption of infected kernels. The Vip3A × Cry1Ab event provided superior protection from the incidence and severity of S. albicosta injury compared to non-Bt or Cry1F hybrids. Insecticide application to a Vip3A × Cry1Ab hybrid did not reduce injury further; however, lower severity of injury was observed for non-Bt and Cry1F hybrids when pyrethroids or diamides were applied at early VT or R1 stages. DON concentrations were reduced with application of prothioconazole fungicide tank-mixed with insecticide at late VT (before silk browning) or when insecticide was applied at early VT followed by prothioconazole at R1. The application of an insecticide/fungicide tank-mix is the most efficient approach for maize hybrids lacking high-dose insecticidal proteins against S. albicosta and F. graminearum tolerance. Results demonstrate that reducing the risk of DON accumulation requires a strategic approach to manage complex associations among S. albicosta, F. graminearum and the environment.

Fusarium ear rot and fumonisins in maize kernels when comparing a Bt hybrid with its non-Bt isohybrid and under conventional insecticide control of Busseola fusca infestations

Maize production in South Africa is negatively affected by Fusarium verticillioides, an endophytic maize pathogen, as well as by Busseola fusca larval damage. Fusarium verticillioides causes ear, stem and root rot, and also produces fumonisin mycotoxins which are toxic to humans and livestock. The African stem borer (Busseola fusca) is a pest of economic importance in maize plants in South Africa. In this study, the interaction between F. verticillioides and B. fusca was investigated to elucidate its effects on Fusarium ear rot and fumonisin production in a Bt hybrid (MON810 event) and its B. fusca-susceptible non-Bt isohybrid. Field trials were conducted over three seasons using a randomised complete block design with six replicates per treatment. The effect of Beta-cyfluthrin (non-systemic, granular) and Benfuracarb (systemic, seed treatment) insecticide applications on the incidence of Fusarium ear rot and fumonisin production in maize was also determined in an unrelated conventional hybrid. For B. fusca infestations, larvae were dispensed into the whorl of each plant at the 12th leaf stage prior to tasselling, while a F. verticillioides MRC826 spore suspension was inoculated through the silks at the silking stage. Maize ears were harvested at physiological maturity and Fusarium ear rot, total fumonisin levels, stem borer damage and target DNA of fumonisin-producing Fusarium spp. quantified. Significantly less Fusarium ear rot and fumonisin were produced in the Bt maize hybrid compared to the non-Bt isohybrid under natural farming conditions, but fungal colonisation and fumonisin production under artificial F. verticillioides inoculation did not differ significantly between the Bt and non-Bt maize. Fumonisin production correlated moderately with the quantity of target DNA of fumonisin-producing Fusarium spp. extracted from maize plants. Benfuracarb application to control stem borer infestation resulted in a significant reduction in Fusarium ear rot and fumonisin production while Beta-cyfluthrin did not. Moreover, B. fusca damage to maize ears significantly increased when both insecticides were not applied to the B. fusca-infested plants. This study indicated that Bt maize and the application of Benfuracarb reduce B. fusca damage to maize ears thereby indirectly reducing Fusarium ear rot and fumonisin production. However, this was not consistent over seasons due to differences in climatic conditions.

The impact ofBacillus thuringiensis technology on the occurrence of fumonisins and other mycotoxins in maize

In many developing countries, maize is both a staple food crop and a widely-used animal feed. However, adventitious colonisation or damage caused by insect pests allows fungi to penetrate the vegetative parts of the plant and the kernels, the latter resulting in mycotoxin contamination. Maize seeds contaminated with fumonisins and other mycotoxins pose a serious threat to both humans and livestock. However, numerous studies have reported a significant reduction in pest damage, disease symptoms and fumonisin levels in maize hybrids expressing theBacillus thuringiensis (Bt) genecry1Ab, particularly in areas where the European corn borer is prevalent. When other pests are also present, thecry1Ab gene alone offers insufficient protection, and combinations of insecticidal genes are required to reduce damage to plants caused by insects. The combination of Cry1Ab protein with other Cry proteins (such as Cry1F) or Vip proteins has reduced the incidence of pests and, indirectly, mycotoxin levels. Maize hybrids expressing multiple Bt genes, such as SmartStax®, are less susceptible to damage by insects, but mycotoxin levels are not routinely and consistently compared in these crops. Bt maize has a greater economic impact onFusarium toxins than aflatoxins. The main factors that determine the effectiveness of Bt hybrids are the type of pest and the environmental conditions, but the different fungal infection pathways must also be considered. An alternative strategy to reduce mycotoxin levels in crops is the development of transgenic plants expressing genes that protect against fungal infection or reduce mycotoxin levels byin situ detoxification. In this review article, we summarise what is known about the relationship between the cultivation of Bt maize hybrids and contamination levels with different types of mycotoxins.

Effectiveness of Bt Maize against Corn Rootworm (Coleoptera: Chrysomelidae) and Species Composition in South Dakota Ten Years Following the Introduction of Transgenic Maize

Corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae), are the most economically important pest of maize in the United States. The larvae consume maize roots, contributing to poor nutrient uptake, lodging of the plants, and severe yield loss. Transgenic maize expressing toxins from the bacterium Bacillus thuringiensis (Bt) have been employed to combat the pest. However, corn rootworm resistance to Bt maize has recently been reported and spurred research on the effectiveness of Bt toxins against corn rootworm across the Corn Belt. Thus, our objectives were twofold. First, we quantified the efficacy of Bt maize hybrids against corn rootworm in South Dakota. Second, we surveyed populations of Diabrotica species in areas where Bt maize had been grown since its commercialization in 2003. Maize hybrids expressing Cry3Bb1, Cry34/35Ab1, and mCry3A were evaluated at two locations with previous corn rootworm infestations or in fields that were in continuous maize for three or more consecutive years. We reported damage to maize expressing Cry3Bb1 and mCry3A toxins. We also observed significantly higher numbers of western corn rootworm than northern corn rootworm in our Diabrotica species surveys, suggesting that western corn rootworm are the dominant species in the region. This research has implications for maize production and sustainable corn rootworm management in South Dakota and the Northern Plains, and will advance our knowledge of the incidence of resistance to Bt toxins and long-term impact of Bt hybrids on species diversity of Diabrotica.

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.

Chronic Responses of Daphnia magna Under Dietary Exposure to Leaves of a Transgenic (Event MON810) Bt–Maize Hybrid and its Conventional Near-Isoline

Insect resistance is the second most common trait globally in cultivated genetically modified (GM) plants. Resistance is usually obtained by introducing into the plant’s genome genes from the bacterium Bacillus thuringiensis (Bt) coding for insecticidal proteins (Cry proteins or toxins) that target insect pests. The aim of this study was to examine the hypothesis that a chronic, high-dose dietary exposure to leaves of a Bt–maize hybrid (GM event MON810, expressing a transgenic or recombinant Cry1Ab toxin), exerted no adverse effects on fitness parameters of the aquatic nontarget organism Daphnia magna (water flea) when compared to an identical control diet based on leaves of the non-GM near-isoline. Cry1Ab was immunologically detected and quantified in GM maize leaf material used for Daphnia feed. A 69-kD protein near Bt’s active core-toxin size and a 34-kD protein were identified. The D. magna bioassay showed a resource allocation to production of resting eggs and early fecundity in D. magna fed GM maize, with adverse effects for body size and fecundity later in life. This is the first study to examine GM-plant leaf material in the D. magna model, and provides of negative fitness effects of a MON810 maize hybrid in a nontarget model organism under chronic, high dietary exposure. Based upon these results, it is postulated that the observed transgenic proteins exert a nontarget effect in D. magna and/or unintended changes were produced in the maize genome/metabolome by the transformation process, producing a nutritional difference between GM-maize and non-GM near-isoline.

Effect of transgenic insect-resistant maize to the community structure of soil nematodes in two field trials

Summary The aim of this study was to determine the effects of Bt maize hybrid cultivation on soil nematode communities in two field trials, as well as to analyse other factors (fertilisation and moisture) responsible for the community structure of soil nematodes. Nematode communities were studied in maize plots at the locality of Borovce in western Slovakia. During 2012 and 2013, hybrids DK440 and DKC3871 (conventional) or DKC4442YG and DKC3872YG (Bt maize, event MON810) were sown in 10 repetitions each. Nematodes were extracted from soil samples collected at the maize flowering (July 11, 2012 and July 30, 2013). Altogether, 39 nematode species belonged to 35 genera were identified in two maize variants. The dominant taxa in both variants were Acrobeloides nanus, Ce-phalobus persegnis, Aphelenchoides composticola, Aphelenchus avenae, Eudorylaimus carteri and Filenchus vulgaris. Calculation of the maturity index, plant parasitic index, enrichment index and structure index did not confirm any clear influence of year or hybrid type on soil nematode communities. The proportional representation of cp-1, cp-2 and cp-3-5 groups of nematode fauna indicated conditions of low stability and high stress. Faunal profiles representing the structure and enrichment conditions of the soil food web showed an environment with a high C:N ratio and high levels of fungal feeders. Based on the calculation of the metabolic footprint of nematodes in the soil food web, a difference between the isoline maize variant and Bt maize variant in 2012 was found, but this difference was not readily apparent in 2013. The occurrence of nematodes, their abundance, proportion of feeding types and selected ecological indices did not depend on the type of maize hybrid (Bt or non-Bt). Thus, the cultivation of genetically modified maize did not directly influence nematode populations. The application of fertiliser at certain periods does not influence the nematode community. The observed significant higher abundance of nematodes was correlated with soil moisture.

Resistencia de insectos a cultivos transgénicos con propiedades insecticidas. Teoría, estado del arte y desafíos para la República Argentina

Los cultivos Bt ejercen alta presión de selección sobre las plagas blanco. Para mitigar la evolución de resistencia, la estrategia Alta Dosis-Refugio (AD-R) requiere: a) una concentración de toxina en la planta suficientemente elevada para provocar que los alelos resistentes sean funcionalmente recesivos; b) baja frecuencia inicial del alelo resistente; c) refugios con plantas no-Bt. Para reforzar la estrategia AD-R, se propone la acumulación de dos o más toxinas en una planta (genes “piramidados”), bajo el supuesto de que estas tienen sitios de acción diferentes, a fin de minimizar el riesgo de resistencia cruzada. Una reciente revisión respalda las fortalezas de la estrategia AD-R en la demora de la evolución de resistencia. El incumplimiento de uno o más componentes de esta estrategia explica los pocos casos de resistencia confirmados. En San Luis, Argentina, se detectaron importantes daños de Diatraea saccharalis en híbridos de maíz Bt. Entre las hipótesis para explicar estos daños, se incluyen dominancia del alelo resistente, baja concentración de toxina y bajo nivel de adopción de refugios. Esto último motiva discusiones sobre la conveniencia de implementar refugios integrados. Se recomienda un abordaje caso por caso para diseñar estrategias de manejo de resistencia de acuerdo a cada plaga.

Baseline sensitivity of maize borers in India to the Bacillus thuringiensis insecticidal proteins Cry1A.105 and Cry2Ab2.

Among the major pests of maize in India are two stem borers, Chilo partellus (Swinhoe) and Sesamia inferens (Walker), and an earworm, Helicoverpa armigera (Hübner). As a pest control strategy, transgenic Bacillus thuringiensis (Bt) maize hybrids are undergoing regulatory trials in India. We have determined the sensitivity of the target lepidopterans to the insecticidal Bt proteins expressed in Bt maize, as this determines product efficacy and the resistance management strategy to be adopted. Maize hybrids with event MON89034 express two insecticidal Bt proteins, Cry1A.105 and Cry2Ab2. Sensitivity profiles of 53 populations of C. partellus, 21 populations of S. inferens and 21 populations of H. armigera, collected between 2008 and 2013 from maize-growing areas in India, to Cry1A.105 and Cry2Ab2 proteins were generated through dose-response assays. Cry1A.105 protein was the most effective to neonates of C. partellus (mean MIC90 range 0.30-1.0 µg mL(-1) ) and H. armigera (mean MIC90 range 0.71-8.22 µg mL(-1) ), whereas Cry2Ab2 (mean MIC90 range 0.65-1.70 µg mL(-1) ) was the most effective to S. inferens. Populations of C. partellus, S. inferens and H. armigera were susceptible to the Bt proteins Cry1A.105 and Cry2Ab2. The Bt sensitivity data will serve as precommercialisation benchmarks for resistance monitoring purposes.

Fumonisins in conventional and transgenic, insect-resistant maize intended for fuel ethanol production: implications for fermentation efficiency and DDGS co-product quality.

Mycotoxins in maize grain intended for ethanol production are enriched in co-product dried distiller’s grains and solubles (DDGS) and may be detrimental to yeast in fermentation. This study was conducted to examine the magnitude of fumonisin enrichment in DDGS and to analyze the impacts of insect injury, Fusarium ear rot severity, and fumonisin contamination on final ethanol yield. Samples of naturally-contaminated grain (0 to 35 mg/kg fumonisins) from field trials conducted in 2008–2011 were fermented and DDGS collected and analyzed for fumonisin content. Ethanol yield (determined gravimetrically) was unaffected by fumonisins in the range occurring in this study, and was not correlated with insect injury or Fusarium ear rot severity. Ethanol production was unaffected in fumonisin B1-spiked grain with concentrations from 0 to 37 mg/kg. Bacillus thuringiensis (Bt) maize often has reduced fumonisins due to its protection from insect injury and subsequent fungal infection. DDGS derived from Bt and non-Bt maize averaged 2.04 mg/kg and 8.25 mg/kg fumonisins, respectively. Fumonisins were enriched by 3.0× for 50 out of 57 hybrid × insect infestation treatment combinations; those seven that differed were <3.0 (1.56 to 2.56×). This study supports the industry assumption of three-fold fumonisin enrichment in DDGS, with measurements traceable to individual samples. Under significant insect pest pressures, DDGS derived from Bt maize hybrids were consistently lower in fumonisins than DDGS derived from non-Bt hybrids.

Transgenic maize hybrids as a tool to control Sesamia cretica Led. compared by conventional method of control on normal hybrids

This study was conducted on Bt and normal maize hybrids during two successive sowing dates, early and late summer plantation. The Sesamia cretica larvae were observed for the first time on first week of April on different commercial maize hybrids. While there was no larva/plant on transgenic maize hybrids, YieldGard and Ageeb-YG, while larvae were found on last week of July by a very little number on maize hybrids for late one. In Early summer planting date showed highly significant differences in reduction percent, between tested compounds and control one, in the pink corn borer population. The bio-residual activity of the NeemAzal-T/S 0.5% on TWC310 was significantly less pronounced, i.e. 75.5%, than other tested ones; the highest percentage of reduction, 86.6%, was achieved by Chlorophan 0.005% on SC2031, followed by NeemAzal-T/S 0.5% on SC2031 83.5% and Chlorophan 0.005% on SC2030 83.4%, respectively. Also the average reduction percentage of S. cretica larvae differed significantly from 69.6%, on NeemAzal-T/S SC2031, to 83.0%, on Chlorophan SC2031, in the late summer planting. The different treatments had positive effects on maize yield in the two planting dates. In the first plantation date, the increased rate of control ranged from 1.04 to 1.24, when NeemAzal-T/S acted on TWC310 and transgenic IYG, respectively. And in the second plantation date, rate of control obtained was 1.06–1.30, when NeemAzal-T/S acted on SC 2031 and transgenic IYG, respectively. The tested compounds played an important role in controlling the pink corn borer insect, S. cretica, and this study suggests that Cry 1Ab-expressing corn hybrids would provide a great value as a component of corn IPM in Egypt.

Impact of multi-resistant transgenic Bt maize on straw decomposition and the involved microbial communities

A general concern associated with the use of transgenic Bt maize is its possible negative influence on non-target organisms and ecosystem functions such as organic matter transformation. Our study was carried out to assess the impact of the multi-resistant Bt maize hybrid MON 89034×MON 88017 on straw decomposition and the residue-colonizing microbial communities in comparison to the near-isogenic control and two conventionally bred varieties. Straw decomposition was analyzed by a substrate-induced respiration method and monitoring of the complete decomposition after 14C pulse labelling of the maize plants. Both approaches indicated significant differences in the decomposition rate between the conventional varieties, but the transgenic Bt hybrid and its near-isogenic control could not be distinguished. Potential effects on the residue-colonizing bacterial and fungal communities were analyzed by the quantification of metabolically active microbial groups using taxon-specific primers and T-RFLP analyses of the small-subunit ribosomal RNA gene. Results obtained over three years and three sampling dates did not reveal significant differences between the transgenic hybrid and the control. The abundance of the metabolically active microbial groups varied between the varieties only in some cases and temporarily restricted. Similarly, T-RFLP analysis did not show an impact of the plant genotype on the bacterial and fungal community structure. In contrast, seasonal effects given by different sampling dates as well as varying soil properties within the field trial were identified as drivers of the microbial communities colonizing the rotting maize straw. Conclusively, the multi-resistant Bt hybrid MON 89034×MON 88017 did not indicate an adverse impact on straw decomposition and the involved microbial communities.

Assessment of the potential impact of a Bt maize hybrid expressing Cry3Bb1 on ground beetles (Carabidae)

The potential impact of a Bt maize hybrid expressing the coleopteran specific Cry3Bb1 on non-target organisms was assessed in a field release experiment. The study examined the relative abundance of ground beetles (Carabidae) in four maize varieties including the genetically engineered DKC 5143-Bt (event MON 88017), its near-isogenic line DKC 5143 and the two conventional varieties DK 315 and Benicia. Pitfall traps were used to collect the ground dwelling arthropods, which were analyzed to species level. Statistical comparisons showed no significant differences of ground beetle activity densities and diversity patterns between the Bt maize and the near isoline. The internal contents of the Bt protein Cry3Bb1 in ground beetles collected from the field were measured with ELISA. The Bt protein was found in 47% of the ground beetles sampled in Bt plots before the anthesis and in 66% of the individuals sampled after the beginning of maize anthesis.

Seasonal dispersal of the Western corn rootworm (Diabrotica virgifera virgifera) adults in Bt and non-Bt maize fields

32 experimental plots were sown at Borovce (district Trnava) in Slovakia during 2008 with 8 maize hybrids, including coleopteran-protected MON 88017, the lepidopteran-protected MON 89034, the stacked product, MON 89034 &amp;times; MON 88017, that same hybrids isoline that did not have the Bt trait or traits, and 4 commercial hybrids. Part of the fourth repetition was unexpectedly infested and damaged with the Western corn rootworm (WCR). High numbers of the WCR adults were found in the damaged plots on July 8. Adult WCR abundance remained concentrated in this area until August 12&amp;ndash;19. The beetles apparently began to disperse during August&amp;nbsp;19&amp;ndash;September 2, and after September 2. The trap captures increased in the uninfested areas up to September&amp;nbsp;16, no significant difference having been found in the adult WCR captures between the infested and uninfested plots, including the plots with MON 88017. Bt-maize hybrids containing MON 88017 strongly influenced the level of the WCR damage as assessed by lodging of the maize plants, and they also influenced the numbers of the WCR adults before maize flowering.&amp;nbsp; We found that intensive movement of the WCR adults from the place of their origin started later in the vegetation season.

Importance of rare taxa for bacterial diversity in the rhizosphere of Bt- and conventional maize varieties

Ribosomal 16S rRNA gene pyrosequencing was used to explore whether the genetically modified (GM) Bt-maize hybrid MON 89034 × MON 88017, expressing three insecticidal recombinant Cry proteins of Bacillus thuringiensis, would alter the rhizosphere bacterial community. Fine roots of field cultivated Bt-maize and three conventional maize varieties were analyzed together with coarse roots of the Bt-maize. A total of 547,000 sequences were obtained. Library coverage was 100% at the phylum and 99.8% at the genus rank. Although cluster analyses based on relative abundances indicated no differences at higher taxonomic ranks, genera abundances pointed to variety specific differences. Genera-based clustering depended solely on the 49 most dominant genera while the remaining 461 rare genera followed a different selection. A total of 91 genera responded significantly to the different root environments. As a benefit of pyrosequencing, 79 responsive genera were identified that might have been overlooked with conventional cloning sequencing approaches owing to their rareness. There was no indication of bacterial alterations in the rhizosphere of the Bt-maize beyond differences found between conventional varieties. B. thuringiensis-like phylotypes were present at low abundance (0.1% of Bacteria) suggesting possible occurrence of natural Cry proteins in the rhizospheres. Although some genera indicated potential phytopathogenic bacteria in the rhizosphere, their abundances were not significantly different between conventional varieties and Bt-maize. With an unprecedented sensitivity this study indicates that the rhizosphere bacterial community of a GM maize did not respond abnormally to the presence of three insecticidal proteins in the root tissue.

Validation of a nested error component model to estimate damage caused by corn rootworm larvae

AbstractThe corn rootworm complex (Coleoptera: Chrysomelidae) constitutes a significant threat to maize production in the United States, and more recently, in Europe. We conducted an analysis of readily available field trial data to validate an existing damage function for corn rootworm larvae. We used a nested error component model with unbalanced panel data to describe the relationship between yield loss and root injury caused by these insects. These data were collected by personnel with the Insect Management and Insecticide Evaluation Programme (Department of Crop Sciences, University of Illinois) and represent 19 location‐years. To our knowledge, this is the largest data set used to estimate a damage function for corn rootworm larvae. Unlike many experiments examining the relationship between root injury and yield loss caused by corn rootworm larvae, the data set used for our analysis includes many Bt maize hybrids. Our model suggests that for each node of roots injured by corn rootworm larvae, a yield loss of approximately 15% can be expected. Statistically significant variance components included an effect of location and experimental error. We speculate that variation in weather across experimental sites was the principal factor contributing to the significant effect of location. The substantial experimental error observed for our model highlights the limitations of utilizing a multi‐year, geographically diverse damage function for predicting yield loss because of root injury on a small scale. We discuss major factors contributing to the variance components estimated by our model and suggest techniques for improving future analyses of the damage function for corn rootworm larvae.

Interaction between maize phenology and transgenic maize hybrids on stalk rots following European corn borer infestation

Field studies were carried out at Hoytville and Wooster, Ohio, USA from 2006 to 2008 to determine the influence of planting date and transgenic Bt maize on incidence and severity of stalk rots of maize. Transgenic and non-transgenic Bt maize hybrids with different maturity ratings were planted on late April/early May, mid-May and early June each year. The incidence and severity of the maize stalk rot complex were compared among planting dates and between Bt and non-Bt genotypes of different relative maturities. Significant linear correlations between European corn borer (Ostrinia nubilalis Hub.) injury to stalk and stalk rots were observed in 2006 and 2007, but not in 2008. We observed significant reduction in stalk discoloration and incidence of maize stalk rot on Bt hybrids compared with non-Bt genotypes. Short season hybrids had significantly lower stalk rots than full season hybrids. The benefit of using Bt hybrids to reduce stalk rots was more evident as planting was delayed than early planting.

Control of Busseola fusca and Chilo partellus stem borers by Bacillus thuringiensis (Bt)--endotoxins from Cry1Ab gene Event MON810 in greenhouse containment trials

Previous testing of several public Bacillus thuringiensis (Bt)-maize events did not show control of the African stem borer (Busseola fusca Fuller), an important stem borer species, without which stewardship would be compromised by the possibility of rapid development of resistance to Bt deltaendotoxins. This study was carried out to test Bt-maize Event MON810 as an option to control all major stem borer species in Kenya. Two Bt-maize hybrids, DKC8073YG and DKC8053YG, both containing Bt Event MON810 of Cry1Ab gene were imported to carry out greenhouse containment trials. The hybrids together with the controls were grown in 10 replications upto the V6 and V8 stages. Infestations on whole plants were carried out at two stages of growth using 5 neonates of the spotted stem borer (Chilo partellus Swinhoe) and B. fusca. Bt-maize Event MON810 hybrids showed resistance to both stem borer species with low leaf damage scores and few surviving larvae recovered from the whole plant. The public Bt-maize Event 223 did not control B. fusca. Deploying Bt-maize Event MON810 may, therefore, be used to control the two species of stem borers. However, the efficacy of Bt-maize Event MON810 will, need to be evaluated under field environments.