Transgenic Bt Research Articles

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.

Effectiveness in the field of Bt rice lines against target pests under various cultural regimes

China has a long history of rice cultivation, incorporating several cultural practices known to influence damage by insect pests. Transgenic Bt rice expresses lepidopteran-specific insecticidal proteins that primarily target lepidopteran insect pests. However, the effectiveness of Bt rice against target insect pests under different cultural regimes has not been evaluated. In this study, the effectiveness of Bt rice lines against rice leaffolder, Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), and striped stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae), was evaluated under various transplanting densities, crop establishment methods, and planting times. The results showed that Bt rice lines (T2A-1 and T1C-19, containing Cry2A and Cry1C, respectively) could prevent damage by these target pests under a range of cultural practices. Injury by C. medinalis or C. suppressalis on rice did not differ with the rice lines under various transplanting densities. Direct-seeded non-Bt rice MH63 suffered heavier injury by C. medinalis and C. suppressalis than it did with transplanting, whereas injury to the two Bt rice lines did not differ with planting methods. Planting time significantly affected injury by C. medinalis or C. suppressalis on non-Bt rice, whereas injury to Bt rice lines did not differ with planting time. These results suggest that transplanting density, planting method, and planting time did not significantly affect the resistance of two Bt rice lines, due to their high insecticidal activity against target insects.

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.

Transgenic cry1C⁎ gene rough rice line T1C-19 does not change the host preferences of the non-target stored product pest, Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae), and its parasitoid wasp, Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae)

Rough rice grains are often stored for extended periods before they are used or consumed. However, during storage, the rough rice is vulnerable to insect infestation, resulting in significant economic loss. Previous studies have shown that volatiles cues, physical characteristics, and taste chemicals on the grains could be the important key behavior factors for storage insect pests to locate the hosts and select oviposition sites. It is also well known that the transgenic Bt rough rice line T1C-19, which expresses a cry1C⁎ gene has a high resistance to Lepidoptera pests. However, there were no evidences to show the consequences of host preference for non-target insect pests after growing Bt transgenic rice. In this study, the potential key factors of Bt rough rice were investigated for their impacts on the behaviors of non-target pest lesser grain borer Rhyzopertha dominica, the main weevil pest of grain and its parasitic wasps Anisopteromalus calandrae, the natural enemy of the beetle. Both electronic nose and electronic tongue analyses showed that the parameters of Bt rough rice were analogous to those of the non-Bt rough rice. The volatile profiles of Bt and non-Bt rough rice examined by gas chromatographic mass spectrometry (GC–MS) were similar. For most volatile compounds, there were no significantly quantitative differences in compound quantities between Bt and non-Bt rough rice. The densities of sclereids and trichomes on the rough rice husk surface were statistically equal in Bt and non-Bt rough rice. The non-target pest, R. dominica, and its parasitoid wasp, A. calandrae, were attracted to both rough rice and could not distinguish the transgenic T1C-19 from the isogenic rough rice. These results demonstrated that Bt rough rice has no negative impacts on the host preference behaviors of non-target stored product pest R. dominica and its parasitoid A. calandrae.

Asiatic cotton can generate similar economic benefits to Bt cotton under rainfed conditions.

American cotton (Gossypium hirsutum L.), transformed with Bacillus thuringiensis Cry genes (Bt G. hirsutum) that confer resistance to lepidopteran pests, is extensively cultivated worldwide. In India, transgenic Bt G. hirsutum was commercially released in 2002 and by 2014 95% of farmers had adopted Bt G. hirsutum(1). The economic benefits of Bt G. hirsutum over non-Bt G. hirsutum are well documented and include increase in yields, increase in farmers' net revenue and reduction in pesticide application against lepidopteran pests(2-9). However, it is unclear to what extent irrigation influences the performance of Bt G. hirsutum on smallholder farming in India, and if, in the absence of irrigation, growing Bt G. hirsutum provides greater economic benefits for Indian smallholder farmers compared with growing the Asiatic cotton Gossypium arboreum L. Here, we compare the economic impact of growing Bt G. hirsutum with growing G. arboreum under rainfed conditions in the Indian state of Maharashtra, and show that G. arboreum can generate similar net revenue, and thus similar economic benefits for smallholder farmers compared with growing Bt G. hirsutum. We also compare the economic impact of growing Bt G. hirsutum under rainfed conditions with growing Bt G. hirsutum under irrigated conditions and show that even though Bt G. hirsutum yields increase with irrigation, the net revenue does not significantly increase because farmers using irrigation spend significantly more than farmers growing Bt G. hirsutum without irrigation. We conclude that our data provide a broader insight into how socio-economic data needs to be incorporated into agro-ecological data when planning strategies to improve cotton farming in India.

Comparative proteomics of Bt-transgenic and non-transgenic cotton leaves

BackgroundAs the rapid growth of the commercialized acreage in genetically modified (GM) crops, the unintended effects of GM crops’ biosafety assessment have been given much attention. To investigate whether transgenic events cause unintended effects, comparative proteomics of cotton leaves between the commercial transgenic Bt + CpTI cotton SGK321 (BT) clone and its non-transgenic parental counterpart SY321 wild type (WT) was performed.ResultsUsing enzyme linked immunosorbent assay (ELISA), Cry1Ac toxin protein was detected in the BT leaves, while its content was only 0.31 pg/g. By 2-DE, 58 differentially expressed proteins (DEPs) were detected. Among them 35 were identified by MS. These identified DEPs were mainly involved in carbohydrate transport and metabolism, chaperones related to post-translational modification and energy production. Pathway analysis revealed that most of the DEPs were implicated in carbon fixation and photosynthesis, glyoxylate and dicarboxylate metabolism, and oxidative pentose phosphate pathway. Thirteen identified proteins were involved in protein-protein interaction. The protein interactions were mainly involved in photosynthesis and energy metabolite pathway.ConclusionsOur study demonstrated that exogenous DNA in a host cotton genome can affect the plant growth and photosynthesis. Although some unintended variations of proteins were found between BT and WT cotton, no toxic proteins or allergens were detected. This study verified genetically modified operation did not sharply alter cotton leaf proteome, and the target proteins were hardly checked by traditional proteomic analysis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12953-015-0071-8) contains supplementary material, which is available to authorized users.

Effect of Seed Blends and Soil-Insecticide on Western and Northern Corn Rootworm Emergence from mCry3A+eCry3.1Ab Bt Maize.

Seed blends containing various ratios of transgenic Bt maize (Zea mays L.) expressing the mCry3A+eCry3.1Ab proteins and non-Bt maize (near-isoline maize) were deployed alone and in combination with a soil applied pyrethroid insecticide (Force CS) to evaluate the emergence of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in a total of nine field environments across the Midwestern United States in 2010 and 2011. Northern corn rootworm, Diabrotica barberi Smith & Lawrence emergence was also evaluated in four of these environments. Both western and northern corn rootworm beetle emergence from all Bt treatments was significantly reduced when compared with beetle emergence from near-isoline treatments. Averaged across all environments, western corn rootworm beetle emergence from 95:5, 90:10, and 80:20 seed blend ratios of mCry3A+eCry3.1Ab: near-isoline were 2.6-, 4.2-, and 6.7-fold greater than that from the 100:0 ratio treatment. Northern corn rootworm emergence from the same seed blend treatments resulted in 2.8-, 3.2-, and 4.2-fold more beetles than from the 100:0 treatment. The addition of Force CS (tefluthrin) significantly reduced western corn rootworm beetle emergence for each of the three treatments to which it was applied. Force CS also significantly delayed the number of days to 50% beetle emergence in western corn rootworms. Time to 50% beetle emergence in the 100% mCry3A+eCry3.1Ab treatment with Force CS was delayed 13.7 d when compared with western corn rootworm beetle emergence on near-isoline corn. These data are discussed in terms of rootworm resistance management.

Transgene expression and Bt protein content in transgenic Bt maize (MON810) under optimal and stressful environmental conditions.

Bt protein content in transgenic insect resistant (Bt) maize may vary between tissues within plants and between plants growing under different environmental conditions. However, it is unknown whether and how Bt protein content correlates with transgene expression, and whether this relationship is influenced by stressful environmental conditions. Two Bt maize varieties containing the same transgene cassette (MON 810) were grown under optimal and stressful conditions. Before and during stress exposure, the upper leaves were analysed for transgene expression using quantitative RT-PCR and for Bt content using ELISA. Under optimal conditions there was no significant difference in the transgene expression between the two investigated Bt maize varieties whereas Bt protein content differed significantly. Transgene expression was correlated with Bt protein content in only one of the varieties. Under stressful environmental conditions we found similar transgene expressions as under optimal conditions but Bt content responded differently. These results suggest that Bt content is not only controlled by the transgene expression but is also dependent on the genetic background of the maize variety. Under stressful conditions the concentration of Bt protein is even more difficult to predict.

A 90 day safety assessment of genetically modified rice expressing Cry1Ab/1Ac protein using an aquatic animal model.

In fields of transgenic Bt rice, frogs are exposed to Bt proteins through consumption of both target and nontarget insects. In the present study, we assessed the risk posed by transgenic rice expressing a Cry1Ab/1Ac fusion protein (Huahui 1, HH1) on the development of Xenopus laevis. For 90 days, froglets were fed a diet with 30% HH1 rice, 30% parental rice (Minghui 63, MH63), or no rice as a control. Body weight and length were measured every 15 days. After sacrificing the froglets, we performed a range of biological, clinical, and pathological assessments. No significant differences were found in body weight (on day 90: 27.7 ± 2.17, 27.4 ± 2.40, and 27.9 ± 1.67 g for HH1, MH63, and control, respectively), body length (on day 90: 60.2 ± 1.55, 59.3 ± 2.33, and 59.7 ± 1.64 mm for HH1, MH63, and control, respectively), animal behavior, organ weight, liver and kidney function, or the microstructure of some tissues between the froglets fed on the HH1-containing diet and those fed on the MH63-containing or control diets. This indicates that frog development was not adversely affected by dietary intake of Cry1Ab/1Ac protein.

Comparative Nutritional Analysis for Marker-Free Transgenic Bt rice and Non-Transgenic Counterparts

Comparative Nutritional Analysis for Marker-Free Transgenic Bt rice and Non-Transgenic Counterparts

Field resistance monitoring of Apolygus lucorum (Hemiptera: Miridae) in Shandong, China to seven commonly used insecticides

Recently, due to the decreased usage of broad-spectrum insecticides in transgenic Bt cotton in China, Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae) has emerged as a major pest of cotton and other agricultural crops. A glass vial bioassay method was used to evaluate the resistance in the Shandong populations of A. lucorum to seven commonly used insecticides during 2009–2014. For organophosphate insecticides, there was no resistance to malathion in most of the collected populations, and resistance ratios were 1.2–5.6-fold for chlorpyrifos in comparison to a susceptible Juye strain. For pyrethroid insecticides, the resistance of three populations (Juye, Huimin and Xiajin) showed an upward tendency during the six studied years, and the resistance levels were 2.0–19.5-fold for bifenthrin and 1.1–8.2-fold for lambda-cyhalothrin, but the efficiency of bifenthrin remained high because its LC50 value was very low (LC50 < 50.9 ng/cm2) compared to the LC50 values of other insecticides. For carbamate insecticides, the resistance ratios ranged from 1.6 to 19.0-fold for methomyl and 1.3–5.5-fold for carbosulfan. For phenylpyrazole insecticides, there was moderate resistance to fipronil (up to 31.3-fold). The resistances of A. lucorum to insecticides have developed slowly in Shandong, except the resistance of the Juye population to fipronil. Therefore, malathion, chlorpyrifos, bifenthrin and carbosulfan can still be employed in integrated pest management (IPM) programs supplemented with physical and biological control methods.

Planting window requirements for Bt cotton in Australia: do they limit the exposure ofHelicoverpaspp. (Lepidoptera: Noctuidae) to Bt toxins?

The threat of Bt resistance in Helicoverpa armigera (Hubner 1808) and H. punctigera (Wallengren 1860) (Heliothinae) is a major impediment to the sustainability of transgenic (Bt) cotton crops in Australia. A resistance management plan has, therefore, been instigated that in part requires farmers to sow their Bt cotton within specified dates to limit the number of generations of Helicoverpa spp. that are exposed to Bt toxins during the growing season. This study evaluated this strategy by utilising industry-wide databases of planting dates and other cropping/pest management events throughout 11 growing seasons. The analysis included model predictions of when Helicoverpa is likely to enter winter (pupal) diapause and emerge as moths in spring, and the long-term pheromone trapping records of moths. In New South Wales and southern Queensland (Qld), most first-generation moths were caught at the same time, or before, cotton was planted (mostly in October). This generation was, therefore, unlikely to have been exposed significantly to Bt toxins as feeding larvae in spring, but some individuals (especially H. armigera) may have been exposed to Bt prior to pupating in the previous autumn. Three subsequent generations, which could have been exposed to Bt during summer–autumn, were recognisable in trap catches before moths became very rare in early April. By then, the majority of Helicoverpa had entered winter diapause as pupae and cotton harvest was well underway. We conclude that the current planting window (pre-mid-November in these regions) achieves little in limiting the exposure of Helicoverpa to Bt. However, insufficient is known of the population dynamics of Helicoverpa in central Qld to be as definitive about the need for planting windows there. Importantly, Helicoverpa are active all year round in central Qld and cotton can be grown over a longer period, thus increasing the risks of greater exposure to Bt.

Transcriptome differences between Cry1Ab resistant and susceptible strains of Asian corn borer.

BackgroundAsian corn borer (ACB), Ostrinia furnacalis (Guenée), is the major insect pest of maize in China and countries of East and Southeast Asia, the Pacific and Australasia. ACB can develop strong resistance to the transgenic Bt maize expressing Cry1Ab, the most widely commercialized Bt maize worldwide. However, the molecular basis for the resistance mechanisms of ACB to Cry1Ab remained unclear. Two biological replicates of the transcriptome of Bt susceptible (ACB-BtS) and Cry1Ab resistant (ACB-AbR) strains of ACB were sequenced using Solexa/Illumina RNA-Seq technology to identify Cry1Ab resistance-relevant genes.ResultsThe numbers of unigenes for two biological replications were 63,032 and 53,710 for ACB-BtS and 57,770 and 54,468 for ACB-AbR. There were 35,723 annotated unigenes from ACB reads found by BLAST searching NCBI non-redundant, NCBI non-redundant nucleotide, Swiss-prot protein, Kyoto Encyclopedia of Genes and Genomes, Cluster of Orthologous Groups of proteins, and Gene Ontology databases. Based on the NOISeq method, 3,793 unigenes were judged to be differentially expressed between ACB-BtS and ACB-AbR. Cry1Ab resistance appeared to be associated with change in the transcription level of enzymes involved in growth regulation, detoxification and metabolic/catabolic process. Among previously described Bt toxin receptors, the differentially expressed unigenes associated with aminopeptidase N and chymotrypsin/trypsin were up-regulated in ACB-AbR. Whereas, other putative Cry receptors, cadherin-like protein, alkaline phosphatase, glycolipid, actin, V-type proton ATPase vatalytic, heat shock protein, were under-transcripted. Finally, GPI-anchor biosynthesis was found to be involved in the significantly enriched pathway, and all genes mapped to the pathway were substantially down-regulated in ACB-AbR.ConclusionTo our knowledge, this is the first comparative transcriptome study to discover candidate genes involved in ACB Bt resistance. This study identified differentially expressed unigenes related to general Bt resistance in ACB. The assembled, annotated transcriptomes provides a valuable genomic resource for further understanding of the molecular basis of ACB Bt resistance mechanisms.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1362-2) contains supplementary material, which is available to authorized users.

Laboratory Evaluation of Transgenic Bt Cotton (cry1Ac +cry2Ab genes) and Non-Bt Cotton against Neonates, First and Second Instar Larvae of Spodoptera litura Fab.

Transgenic Bt cotton BG II (cry1Ac +cry2Ab genes) in comparison with non-Bt cotton were evaluated for their effect on the development of Spodoptera litura in the IPM Laboratory of Department of Entomology, Punjab Agricultural University Ludhiana. The leaf and square of various Bt cotton cultivars viz. MRC 7017, BCHH 6488, BCHH 6588, Ankur 3028, NCS 855 and non-Bt cotton LH 2076 were fed to the neonates, first and second instars larvae of cotton leaf worm, S. litura. The neonates, 1st and 2nd instar larvae when fed on leaves of transgenic Bt cotton resulted in 100 per cent mortality as compared to non-Bt cotton (0.00). However, 2nd instar larvae fed on squares of Bt cotton resulted in 100 per cent mortality in most of the Bt cotton cultivars, MRC 7017, BCHH 6488, BCHH 6588 and Ankur 3028 except NCS 855 (82.16) and non-Bt (6.63). The developmental times of 2nd instar larvae of S. litura were different among Bt cotton cultivars and non-Bt cotton. The survived 3rd instar larvae fed on leaves in Ankur 3028 (11.11) followed by BCHH 6588 (7.14) and BCHH 6488 (7.4) continued to be 3rd instar even after 17 days, while those on non Bt cotton moulted to pupal stage (7.14). However, when larvae fed on squares of Bt cotton and non-Bt cotton, maximum pupation takes place in non Bt cotton cultivar, LH 2076 (93.33) followed by Bt cotton cultivar NCS 855 (17.85) after 24 days. The total developmental time of larvae in the Bt cotton was significantly longer than that of larvae on non-Bt squares. The higher weight of larvae fed on leaves was recorded in LH 2076 (19.72 mg). Similarly, after 10 days of release of S. litura on squares of different cotton cultivars higher weight of larvae was recorded in LH 2076 (25.671 mg) and lower in MRC 7017 (2.919 mg). The pupae that developed from the larvae that fed on non-Bt were heavier than those that developed from the larvae that fed on non-Bt cotton squares. After 27 days, 100 per cent adult emergence was recorded in non-Bt cotton cultivar, LH 2076 followed by single emergence in BG II cotton cultivar NCS 855. However, after 31 days, four adults were formed in case of NCS 855 but they were not able to survive for more than 2 days and all of them were males. It can be inferred that all BGII cotton cultivars were toxic to neonates, first and second instar larvae of S. litura under laboratory conditions.

Comparative susceptibility of transgenic Bt cotton hybrids to Earias spp. and other non-target insects

Four Bt cotton (Gossypium hirsutum L.) hybrids, each with one of four different events, viz., MRC 6301 Bt (cry1Ac gene), JKCH 1947 Bt (modified cry1Ac gene), NCEH 6R Bt (fusion cry1Ac/cry1Ab gene) and MRC 7017 Bollgard II (cry1Ac and cry2Ab genes) were evaluated along with their respective isogenic non-Bt genotypes against Earias spp., sucking insect pests, and predators in 2010 and 2011. Female oviposition was not significantly different between Bt and non-Bt cotton hybrids. All Bt cotton hybrids recorded significantly reduced damage of Earias spp. in shoots, squares, green bolls and freshly shed fruiting bodies as compared to the isogenic non-Bt genotypes. In 2010, the incidence of Earias spp. was observed only on 136 day old crop or later. MRC 7017 Bollgard II had the lowest damage followed by NCEH 6R Bt, MRC 6301 Bt and JKCH 1947 Bt. However, no damage was observed in any of the Bt hybrids throughout the cropping season in 2011. The time of first appearance of Earias spp. on Bt cotton differed from non-Bt genotypes, whereas, first appearance of sucking insects and predators did not differ between Bt and their isogenic non-Bt genotypes. Populations of sucking insect pests {Amrasca biguttula biguttula (Ishida), Bemisia tabaci (Gen.) and Thrips tabaci (Lindemann)} varied significantly among different cotton genotypes. Nevertheless, their incidence on Bt cotton hybrids did not differ significantly from the respective isogenic non-Bt genotypes. No significant differences were observed with respect to relative abundance of predators, viz., spiders, chrysopids and coccinellids on Bt and non-Bt cotton genotypes. All Bt cotton hybrids out-yielded their isogenic non-Bt genotypes during both years. The yield was significantly higher in MRC 7017 Bollgard II followed by MRC 6301 Bt, NCEH 6R Bt and JKCH 1947 Bt. The selection of superior genotypes with better yield characteristics is thus vital for developing high yielding transgenic cotton.

A de novo transcriptomic analysis to reveal functional genes in Apolygus lucorum.

The widespread planting of genetically engineered cotton producing the Cry1Ac toxin has led to significantly reduced pesticide applications since 1997. However, consequently, the number of green mirid bugs (GMB), Apolygus lucorum (Meyer-Dür) has increased. So far the GMB, instead of the cotton bollworm Helicoverpa armigera (Hübner), has become the major pest in the transgenic Bt cotton field and has influenced cotton yield. Disproportionately, only a few studies on GMB at molecular level have been reported. Libraries from both third instar nymphs and adults were sequenced using Illumina technology, producing more than 106 million short reads and assembled into 63029 unigenes of mean length 597 nt and N50 813 nt, ranging from 300 nt to 9771 nt. BLASTx analysis against Nr, Swissprot, GO and COG was performed to annotate these unigenes. As a result, 26478 unigenes (42.01%) matched to known proteins and 107 immune-related, 320 digestive-related and 53 metamorphosis-related genes were detected in these annotated unigenes. Additionally, we profiled gene expression using mapping based differentially expressed genes (DEGs) strategy between the two developmental stages: nymph and adult. The results demonstrated that thousands of genes were significantly differentially expressed at different developmental stages. The transcriptome and gene expression data provided comprehensive and global gene resources of GMB. This transcriptome would improve our understanding of the molecular mechanisms of various underlying biological characteristics, including development, digestion and immunity in GMB. Therefore, these findings could help elucidate the intrinsic factors of the GMB resurgence, offering novel pest management targets for future transgenic cotton breeding.

A 3-year field investigation of impacts of Monsanto’s transgenic Bt-cotton NC 33B on rhizosphere microbial communities in northern China

Monsanto’s Bt-cotton NC 33B, planted in northern China for more than one decade, effectively controls cotton bollworms and decreases the use of chemical insecticides. Because of the concern about undesirable ecological side-effects of transgenic Bt-cottons, it is important to assess Bt-cotton NC 33B’s effects on soil microorganisms in this zone. Microbial communities in the rhizosphere soil of Bt and non-Bt cottons were monitored under field conditions by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints of eubacteria, fungi and actinomycetes at six growth stages after three-year cultivation. Results showed that the population sizes and community structures of eubacteria, fungi and actinomycetes in rhizosphere soil were markedly affected by natural variations in the environment related to cotton growth stages. However, there was no significant difference in eubacterial, fungal and actinomycete population size and community structures in rhizosphere soil between NC 33B and its non-transgenic parent. In general, Bt-cotton NC 33B did not show evident effects on microbial communities in the rhizosphere soil under field conditions after three-year cultivation. This study provides a theoretical basis for environmental impact monitoring of transgenic Bt cottons.

Optimizing pyramided transgenic Bt crops for sustainable pest management.

Transgenic crop pyramids producing two or more Bacillus thuringiensis (Bt) toxins that kill the same insect pest have been widely used to delay evolution of pest resistance. To assess the potential of pyramids to achieve this goal, we analyze data from 38 studies that report effects of ten Bt toxins used in transgenic crops against 15 insect pests. We find that compared with optimal low levels of insect survival, survival on currently used pyramids is often higher for both susceptible insects and insects resistant to one of the toxins in the pyramid. Furthermore, we find that cross-resistance and antagonism between toxins used in pyramids are common, and that these problems are associated with the similarity of the amino acid sequences of domains II and III of the toxins, respectively. This analysis should assist in future pyramid design and the development of sustainable resistance management strategies.

Development of Clitoria ternatea as a biopesticide for cotton pest management: assessment of product effect on Helicoverpa spp. and their natural enemies

AbstractThe Australian cotton industry is now dominated by transgenic (Bt) varieties, which provide a strong platform for integrated pest management (IPM) of Helicoverpa spp. (Lepidoptera: Noctuidae). New IPM‐compatible tools are required to manage the development of resistance in Helicoverpa spp. and the control of other sucking pests. A 10‐year study commenced in 2001 to identify short‐range, non‐volatile compounds on organ surfaces of plants that deter feeding or oviposition, or are toxic and do not support development of Helicoverpa spp. on cotton plants. The results of the initial study identified Clitoria ternateaL. (Fabaceae) as non‐preferred for Helicoverpa spp. oviposition and larval feeding. The study found that C. ternatea fractionalized extract mixture (fractions 2, 3, 4, and 6) caused oviposition and feeding deterrence as well as direct toxicity to Helicoverpa spp. This study has developed an oil‐based semiochemical product from C. ternatea identified in the initial study into a potential commercial product. The application of 1–2% (vol/vol) of the oil‐based formulation of the C. ternatea mixture against Helicoverpa spp. on commercial transgenic and conventional cotton crops resulted in Helicoverpa spp. oviposition and larval feeding deterrence, as well as caused direct mortality to larvae. No negative effect on beneficial insects was observed. In conclusion, the ability of the oil‐based C. ternatea mixture to control Helicoverpa spp. infestations, while conserving beneficial insect populations, suggests its potential for use in supplementing IPM programs to reduce the use of synthetic insecticides on transgenic and conventional cotton crops.

Potential for and consequences of naturalized Bt products: Qualitative dynamics from indirect intransitivities

Advances in genetic modification technology and the production of human-altered genomes have led to an array of genetically modified organisms utilized to address numerous global issues. The human need-based development of these modified organisms often presents unprecedented phenotypes which will interact with the world's existing biodiversity in unknown ways. One such example is Bt transgene crops proliferating because of their application to food security issues due to their resistance to pest insects. While threats to long term viability of Bt crop use due to resistance evolution in pests have been extensively investigated, issues regarding the effects of Bt transgene crops on existing ecosystems and the biodiversity contained therein have seen less scrutiny. In particular, the long-term dynamics in the case of a naturalized Bt product has not received the attention it deserves. Here we note that the ecosystem structure emerging from a naturalized Bt crop is, qualitatively, an intransitive loop. Based on this structure we develop a simple ecosystem model showing that the intransitive nature of the system has potential to facilitate long term persistence of naturalized Bt transgenes by shifting community dynamics.