Event MON810 Research Articles

Effects of Bt Corn and Egg Density on Western Corn Rootworm (Coleoptera: Chrysomelidae) Adult Emergence and Estimation of Effective Bt Dose.

Since 2003, rootworm-protected transgenic corn has been commercially deployed in the United States as a principal method of control of western corn rootworm, Diabrotica virgifera virgifera LeConte. Durability of this technology depends partly on larval mortality ("dose") exerted by the traits, but density-dependent mortality can confound calculations of dose. Research reported here examined the effects of density-dependent mortality on adult emergence and estimates of trait dose. At sites in Illinois and Indiana, western corn rootworm eggs were infested at four densities on non-Bt corn and at a single density on corn hybrids with transgenic events MON 88017 (VT Triple PRO), DAS-59122-7 (Herculex Insect Protection), and MON 88017 × DAS-59122-7 (SmartStax corn). Beetles were collected weekly in large emergence cages. Density-dependent mortality and the effect of Bt traits were examined using percent survival from egg to adult, sex ratio, and beetle mass. Beetle emergence from Bt treatments was very low, and percent survival from non-Bt treatments was greatest at the lowest egg density (410 eggs per row-meter). Therefore, emergence from the lowest infestation density on non-Bt corn was used to estimate the effective dose of the Bt treatments. Sex ratio and beetle mass were unaffected by density-dependent effects and were not consistently affected by Bt traits. Dose was estimated at 97.4-99.3% for MON 88017, 98.8-99.9% for DAS-59122-7, and 99.7-100.0% for MON 88017 × DAS-59122-7. This study confirms the need to account for density-dependent mortality when estimating dose of corn rootworm protection events even at relatively low egg infestation densities.

Performance of Cry1Ab‐susceptible and ‐heterozygous resistant populations of sugarcane borer in sequential feedings on non‐Bt and Bt maize plant tissue

AbstractA seed mix strategy has been used to provide refuge to susceptible insects for resistance management in planting transgenic maize expressing Bacillus thuringiensis Berliner (Bt) proteins. To determine whether larval movement in a seed mix planting creates favorable conditions for resistant heterozygotes of a target pest, performance of Cry1Ab‐susceptible (SS) and ‐heterozygous resistant (RS) populations of the sugarcane borer, Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae), was evaluated in sequential feeding on non‐Bt and Cry1Ab (event MON 810) maize plant tissue. For each insect population, nine feeding sequences were employed. SS and RS feeding on non‐Bt plants for their entire larval stages survived well and >60% of the adult pairs produced viable eggs, with an average of 269 progeny per female, whereas none of the two populations on Bt maize plants survived to the pupal stage. SS larvae could not develop to adults if the larvae fed on non‐Bt plants for ≤15 days and then moved to Bt plants. In contrast, 4.2–29.2% of RS larvae that fed on non‐Bt plants for ≥9 days and then moved to Bt plants developed to adults, and 63.6% of pairs of these adults produced viable eggs, with an average of 185 progeny per female. For SS larvae that fed on Bt plants for 1 or 2 days and then moved to non‐Bt plants, few larvae developed to adults with varied emergence times, whereas 28.1 and 13.5% RS larvae feeding on Bt plants for 1 and 2 days, respectively, successfully developed to adults; 43.8% of pairs of these adults produced viable eggs, with an average of 220 progeny per female. For the case of the single Bt gene maize plants (event MON 810), the results suggest that RS insects may have advantages in survival and reproduction over SS if RS larvae hatch and feed on Bt plants during the first 1 or 2 days and then move to non‐Bt plants. This advantage is less for RS larvae that hatch and feed on non‐Bt plants first and then move to Bt plants, unless the larval movement occurs in the later stages (e.g., fourth or fifth instars).

Relevance of new scientific evidence on the occurrence of teosinte in maize fields in Spain and France for previous environmental risk assessment conclusions and risk management recommendations on the cultivation of maize events MON810, Bt11, 1507 and GA21

Relevance of new scientific evidence on the occurrence of teosinte in maize fields in Spain and France for previous environmental risk assessment conclusions and risk management recommendations on the cultivation of maize events MON810, Bt11, 1507 and GA21

Resistance of Bt-maize (MON810) against the stem borers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) and its yield performance in Kenya

A study was conducted to assess the performance of maize hybrids with Bt event MON810 (Bt-hybrids) against the maize stem borer Busseola fusca (Fuller) in a biosafety greenhouse (BGH) and against the spotted stem borer Chilo partellus (Swinhoe) under confined field trials (CFT) in Kenya for three seasons during 2013–2014. The study comprised 14 non-commercialized hybrids (seven pairs of near-isogenic Bt and non-Bt hybrids) and four non-Bt commercial hybrids. Each plant was artificially infested twice with 10 first instar larvae. In CFT, plants were infested with C. partellus 14 and 24 days after planting; in BGH, plants were infested with B. fusca 21 and 31 days after planting. In CFT, the seven Bt hybrids significantly differed from their non-Bt counterparts for leaf damage, number of exit holes, percent tunnel length, and grain yield. When averaged over three seasons, Bt-hybrids gave the highest grain yield (9.7 t ha−1), followed by non-Bt hybrids (6.9 t ha−1) and commercial checks (6 t ha−1). Bt-hybrids had the least number of exit holes and percent tunnel length in all the seasons as compared to the non-Bt hybrids and commercial checks. In BGH trials, Bt-hybrids consistently suffered less leaf damage than their non-Bt near isolines. The study demonstrated that MON810 was effective in controlling B. fusca and C. partellus. Bt-maize, therefore, has great potential to reduce the risk of maize grain losses in Africa due to stem borers, and will enable the smallholder farmers to produce high-quality grain with increased yield, reduced insecticide inputs, and improved food security.

Relevance of a new scientific publication (Hofmann et al., 2016) for previous environmental risk assessment conclusions and risk management recommendations on the cultivation of Bt‐maize events MON810, Bt11 and 1507

Relevance of a new scientific publication (Hofmann et al., 2016) for previous environmental risk assessment conclusions and risk management recommendations on the cultivation of Bt‐maize events MON810, Bt11 and 1507

Relevance of a new scientific publication (Bøhn et al., 2016) for previous environmental risk assessment conclusions on the cultivation of Bt‐maize events MON810 and Bt11

Relevance of a new scientific publication (Bøhn et al., 2016) for previous environmental risk assessment conclusions on the cultivation of Bt‐maize events MON810 and Bt11

Evaluation of adult emergence and larval root injury for Cry3Bb1‐resistant populations of the western corn rootworm

AbstractThe transgenic maize (Zea mays L.) event MON 88017 produces the Bacillus thuringiensis Berliner (Bt) toxin Cry3Bb1 to provide protection from western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding. In response to reports of reduced performance of Cry3Bb1‐expressing maize at two locations in Illinois, we conducted a two‐year experiment at these sites to characterize suspected resistance, as well as to evaluate root injury and adult emergence. Single‐plant bioassays were performed on larvae from each population that was suspected to be resistant. Results indicate that these populations had reduced mortality on Cry3Bb1‐expressing maize relative to susceptible control populations. No evidence of cross‐resistance between Cry3Bb1 and Cry34/35Ab1 was documented for the Cry3Bb1‐resistant populations. Field studies were conducted that included treatments with commercially available rootworm Bt hybrids and their corresponding non‐Bt near‐isolines. When compared with their near‐isolines, larval root injury and adult emergence were typically reduced for hybrids expressing Cry34/35Ab1 either alone or in a pyramid. In many instances, larval root injury and adult emergence were not significantly different for hybrids expressing mCry3A or Cry3Bb1 alone when compared with their non‐Bt near‐isolines. These findings suggest that Cry34/35Ab1‐expressing Bt maize may represent a valuable option for maize growers where Cry3Bb1 resistance is either confirmed or suspected. Consistent trends in adult size (head capsule width and dry mass) for individuals recovered from emergence cages were not detected during either year of this experiment. Because of the global importance of transgenic crops for managing insect pests, these results suggest that improved decision‐making for insect resistance management is needed to ensure the durability of Bt maize.

Assessing the potential for interaction between the insecticidal activity of two genetically engineered cotton events combined by conventional breeding: An example with COT102 × MON 15985

Bollgard® III was developed by combining cotton events COT102 and MON 15985 through conventional breeding to improve efficacy against lepidopteran feeding damage. COT102 produces the Vip3Aa19 protein and MON 15985 produces the Cry1Ac and Cry2Ab2 proteins. COT102 × MON 15985 has also been bred with Roundup Ready Flex® cotton (MON 88913) that confers glyphosate tolerance. This study evaluated the activity of COT102 and MON 15985 and the combined activity of COT102 and MON 15985 against the cotton bollworm (CBW, Helicoverpa zea). COT102, MON 15985, COT102 × MON 15985 and COT102 × MON 15985 × MON 88913 have comparable Vip3Aa19 and/or Cry1Ac, Cry2Ab2 protein expression levels as determined by enzyme-linked immunosorbent assay. CBW demonstrated concentration-dependent growth inhibition after 7-days of feeding on lyophilized leaf tissue derived from COT102, MON 15985, COT102 × MON 15985 and COT102 × MON 15985 × MON 88913 incorporated into an artificial diet. Observed EC50 values for COT102 × MON 15985 and COT102 × MON 15985 × MON 88913 were comparable (≤4% deviation) with the predicted EC50 value under the assumption of additivity using the combined activity of COT102 and MON 15985. No interaction in biological activity between COT102 and MON 15985 is consistent with results from competition and ligand blotting assays that demonstrated that Vip3Aa does not inhibit the binding of either Cry1Ac or Cry2Ab2 and vice versa. The results from this study demonstrate that the activity of COT102 × MON 15985 against CBW is consistent with predictions of additivity.

Farm‐level GM Coexistence Policies in the EU: Context, Concepts and Developments

SummaryMany EU MS have implemented coexistence policies to govern the cultivation of GM crops on their territory but only one GM crop, the Bt maize event MON810, is currently cultivated in the EU. From a practical point of view, a combination of paper traceability and implementation of isolation distances between GM and non‐GM maize are considered as being the most effective way of segregating both types of materials. In general, infringements will however only become apparent after harvesting the crops. Liability issues will then be invoked late in the process restricting or at least limiting flexibility in the marketing of the materials in an appropriate way. Nevertheless, following the general guidelines for coexistence developed by the European Commission, EU Member States are progressively regulating coexistence at the national level. The policies in the EU governing coexistence can be differentiated into ex‐ante regulations and ex‐post liability rules. This differentiation is useful as the economic implications between the two differ. With regard to maize, studies show that the costs of complying with the given threshold values for GM content at farm level range from zero to 2 per cent of the total growing costs for both conventional and organic production.

Frequency of Bacillus thuringiensis Cry1A.105 resistance alleles in field populations of the fall armyworm, Spodoptera frugiperda, in Louisiana and Florida

Fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major pest of many crops and a cross-crop target of transgenic maize, cotton, and soybean containing Bacillus thuringiensis (Bt) genes. Some of the current Bt maize products for controlling lepidopteran species contain the Bt event MON 89034. The objective of this study was to determine the frequency of resistance alleles in field populations of S. frugiperda collected from Louisiana and Florida, U.S. to Cry1A.105, one of the two Bt genes in MON 89034. A total of 150 F2 two-parent families of S. frugiperda were established using single-pair mating of field-collected individuals in 2011, which included 79 families from two locations in Louisiana and 71 families from one location in Florida. F2 screen was conducted to detect resistance alleles in these families to Cry1A.105 protein in maize plants. Four out of the 79 Louisiana and 14 out of the 71 Florida families were identified to possess resistance alleles to the Cry1A.105 maize plants. Thus, the corresponding frequency of resistance alleles to Cry1A.105 maize was estimated to be 0.0158 with a 95% credibility interval (CI) of 0.0052–0.0323 for the Louisiana populations and 0.0559 with a 95% CI of 0.0319–0.0868 for the Florida populations. The resistant families survived on whole Cry1A.105 maize plants and demonstrated a significant level (>116-fold) of resistance to the Cry1A.105 protein in a diet-incorporated bioassay. These findings suggest that resistance allele frequency in S. frugiperda to single-gene Cry1A.105 maize in the U.S. southeast region apparently is not rare, most likely due to the selection of Cry1F resistance and its cross-resistance to Cry1A.105.

Effects of three-year cultivation of Cry1Ab-expressing Bt maize on soil microarthropod communities

The impact of Cry1Ab-expressing Bt maize (event MON810) on non-target fauna has been a major concern since its deployment in Europe. In this paper, we have assessed the levels of Cry1Ab in rhizosphere soil samples from a Bt maize crop and evaluated the potential effects of Bt maize on soil microarthropods by a three-year trial in an experimental farm-scale field in Central Spain. The Cry1Ab toxin was detected in decaying soil organic matter (OM) from Bt maize plots up to three months after harvest, with values ranging between 0.10 and 0.18ng Cry1Ab/mg OM, but it showed low insecticidal activity. The study focused on Acari and Collembola, the two major components of the soil microarthropod community. They accounted for 88% of the total specimens collected, and they were identified at the suborder and species level, respectively. Interestingly, Cry1Ab was detected for the first time in field collected collembolans, Entomobrya spp., demonstrating their exposure to the toxin. The abundance of mites and collembolans and the frequency of occurrence of the main collembolan species did not rely on the type of maize except for Parisotoma notabilis, more abundant and frequent in Bt maize plots. However, significant differences among years were common in both groups. Noticeably, we found higher values of species richness and diversity of collembolans in Cry1Ab-expressing Bt maize than in non-Bt plots, which could be explained under different scenarios. Our results suggest that continuous cultivation of Bt maize does not negatively affect soil microarthropods, indicating that Bt maize could be compatible with this community.

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.

Flea beetles (Coleoptera: Chrysomelidae, Alticinae) in Bt- (MON810) and near isogenic maize stands: Species composition and activity densities in Hungarian fields

Flea beetles (Chrysomelidae, Alticinae) were collected with Pherocon AM yellow sticky traps in maize plots to compare the assemblages from transgenic Bt- (genetic event MON810, producing Cry1Ab protein effective against lepidopteran pests) and near isogenic maize in Hungary. Altogether, 51,348 flea beetle individuals from 26 species were collected. The dominant species were Phyllotreta atra (F.) and Phyllotreta vittula (Redtenbacher). Their abundances along with other (non-P. atra and non-P. vittula) flea beetle species showed no significant differences between Bt- and isogenic maize plots. Similarly, no difference was found between Bt maize and isogenic maize plots in the species richness of the flea beetle assemblages.

Cry1Ab protein from Bacillus thuringiensis and MON810 cry1Ab-transgenic maize exerts no adjuvant effect after airway exposure.

The genetically modified (GM) maize event MON810 has been inserted with a processed version of the transgene, cry1Ab, derived from the soil bacterium Bacillus thuringiensis (Bt) to express proteins with insecticidal properties. Such proteins may introduce new allergens and also act as adjuvants that promote allergic responses. While focus has been on safe consumption and hence the oral exposure to GM food and feed, little is known regarding inhalation of pollen and desiccated airborne plant material from GM crops. The aim of this study was to investigate whether plant material from the Cry1Ab-expressing maize variety MON810, or trypsin-activated Cry1Ab (trypCry1Ab) protein produced in recombinant bacteria, may act as adjuvants against the allergen ovalbumin (OVA) in a mouse model of airway allergy. A clear proallergic adjuvant effect of the mucosal adjuvant cholera toxin (CT) was demonstrated, determined as increased specific IgE, eosinophils and Th2 cytokines in MLN cell supernates, while no elevation in OVA-specific antibodies or cytokine release from MLN cells after stimulation with OVA were observed in mice receiving Cry1Ab-containing plant materials or the trypCry1Ab protein. Our data suggest that Cry1Ab proteins had no detectable systemic adjuvant effect in mice after airway exposure. Further experiments with purified plant proteins, as well as long-term exposures needs be conducted to further evaluate exposures experienced in real-life situations.

Comparative study of transgenic and non-transgenic maize (Zea mays) flours commercialized in Brazil, focussing on proteomic analyses

Genetically modified foods are a major concern around the world due to the lack of information concerning their safety and health effects. This work evaluates differences, at the proteomic level, between two types of crop samples: transgenic (MON810 event with the Cry1Ab gene, which confers resistance to insects) and non-transgenic maize flour commercialized in Brazil. The 2-D DIGE technique revealed 99 differentially expressed spots, which were collected in 2-D PAGE gels and identified via mass spectrometry (nESI-QTOF MS/MS). The abundance of protein differences between the transgenic and non-transgenic samples could arise from genetic modification or as a result of an environmental influence pertaining to the commercial sample. The major functional category of proteins identified was related to disease/defense and, although differences were observed between samples, no toxins or allergenic proteins were found.

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.

Native Maize Resistance to Corn Earworm, Helicoverpa zea1, and Fall Armyworm, Spodoptera frugiperda1, with Notes on Aflatoxin Content

Fifteen genotypes of maize, Zea mays L., varying from putatively resistant to susceptible to corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae), based on visual observations in a breeding nursery, were evaluated for leaf and ear injury, yield, and aflatoxin content in an open field experiment. The genotypes were nine nontransgenic inbred lines and six hybrids including a Bt hybrid containing transgene events MON810 and MON88017. Larval development and progressive leaf injury were measured on selected genotypes in companion laboratory larval feeding and field-cage experiments. Resistance to corn earworm was confirmed for one nontransgenic inbred line in the open field as observed by significantly less ear injury with deepest penetration of larval feeding as low as 1.61 cm and total surface area as low as 1.44 cm2, compared to injury of susceptible genotypes (e.g., depth of penetration as high as 7.53 cm and surface ear injury as high as 14.16 cm2). The low injury of the putative resistant genotype approached the low ear injury seen in the transgene Bt hybrid. Fall armyworm was not abundant in the open field, and injury scores were not significant different across genotypes, ranging from 1.15 to 3.33 (using the 1–9 leaf injury scale). But putative resistance to fall armyworm was indicated in one genotype in field cages as observed by less leaf injury 7 to 24 days after artificial infestation compared with a susceptible genotype. Related to yield, kernel weight of the inbred genotypes (as low as 205 kg/ha) was significantly less than kernel weight of the hybrids (as high as 2599 kg/ha), but there was no apparent relationship of yield with plant injury. Few differences in aflatoxin content were observed, but variability was great, average 52 to 2838 ppb across genotypes. One genotype resistant to corn earworm was referred for advanced breeding and testing for resistance to multiple stresses, with the aim to include native resistance to the insects into the genetic background of high-yielding maize, including Bt hybrids, grown in the southern U.S. Further observations of three genotypes were recommended before consideration for advanced breeding.

Impact of coleopteran-active Bt corn on non-target nematode communities in soil and decomposing corn roots

Genetically engineered corn expressing crystalline proteins for insect control and encoded by genes derived from soil bacterium Bacillus thuringiensis (Bt) are widely adopted in the United States. Among the seven different events of Bt corn available commercially, YieldGard® Rootworm (event MON863) expresses a variant of the cry3Bb1 protein in the root tissue to control corn rootworm larvae. Nematodes reside in the rhizosphere and are potentially exposed to Cry3Bb1 toxins exudated from roots of Bt corn. We test the hypothesis that coleopteran-active Bt corn does not affect non-target soil nematodes. Experimental treatments were: 1) a Bt hybrid, 2) a non-Bt isoline treated with a conventional soil insecticide, and 3) a non-Bt isoline without insecticide. Nematodes were extracted from soil samples collected prior to planting (May), at peak anthesis (August), and after harvest (October) in 2003 and 2004, enumerated and identified to genus. A total of 73 nematode genera were encountered in soil and litter combined. During the growing season, maturity index values and relative abundance of fungivorous nematodes were greater in the Bt hybrid than the non-Bt isoline with or without insecticide. Nematode trophic diversity values were greater in the Bt hybrid than non-Bt isoline with insecticide and this effect continued through the following spring. Abundance of nematode predators increased two weeks after insecticide was applied to non-Bt isoline, but decreased without insecticides on either Bt or the non-Bt isoline. In decaying roots of corn treatments, maturity index values and the relative abundance of nematode predators was greater in the Bt hybrid than non-Bt isoline with insecticide. Effects at the overall community structure and nematode genera varied more by seasonal phenology than corn treatment. The isoline with insecticide had more non-target effects on nematode communities than the Bt hybrid. This treatment increased the relative abundance of predaceous nematodes temporarily but eventually reduced successional maturity by harvest time, which continued to decline during the winter in both soil and decaying corn roots.

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.