Showing papers on "Bacillus thuringiensis published in 2011"
TL;DR: Recently, similar Cry-binding proteins have been identified in the three insect orders, as cadherin, aminopeptidase-N and alkaline phosphatase suggesting a conserved mode of action, suggesting a significant reduction in chemical insecticide use.
885 citations
TL;DR: Recent progress in the development of Bt technology and the countermeasures that have been introduced to prevent the evolution of resistant insect populations are reviewed.
Abstract: Bacillus thuringiensis (Bt) is a soil bacterium that forms spores during the stationary phase of its growth cycle. The spores contain crystals, predominantly comprising one or more Cry and/or Cyt proteins (also known as δ-endotoxins) that have potent and specific insecticidal activity. Different strains of Bt produce different types of toxin, each of which affects a narrow taxonomic group of insects. Therefore, Bt toxins have been used as topical pesticides to protect crops, and more recently the proteins have been expressed in transgenic plants to confer inherent pest resistance. Bt transgenic crops have been overwhelmingly successful and beneficial, leading to higher yields and reducing the use of chemical pesticides and fossil fuels. However, their deployment has attracted some criticism particularly with regard to the potential evolution of pest-resistant insect strains. Here, we review recent progress in the development of Bt technology and the countermeasures that have been introduced to prevent the evolution of resistant insect populations.
632 citations
TL;DR: This is the first report of field-evolved resistance to a Bt toxin by the western corn rootworm and by any species of Coleoptera, and suggests that improvements in resistance management and a more integrated approach to the use of Bt crops may be necessary.
Abstract: Background
Crops engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are planted on millions of hectares annually, reducing the use of conventional insecticides and suppressing pests. However, the evolution of resistance could cut short these benefits. A primary pest targeted by Bt maize in the United States is the western corn rootworm Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae).
601 citations
TL;DR: Drought stress affected growth of isolates as indicated by increased intracellular free amino acids, proline, total soluble sugars, and exopolysaccharides, while inoculated maize seedlings showed physiological response that could alleviate drought stress negative effects.
Abstract: In present study Bacillus spp. screened for drought tolerance could tolerate minimal water potential (-0.73 MPa) were evaluated for plant growth promoting properties at –0.73 MPa. Drought stress affected growth of isolates as indicated by increased intracellular free amino acids, proline, total soluble sugars, and exopolysaccharides. Drought-tolerant Bacillus spp. HYD-B17, HYTAPB18, HYDGRFB19, BKB30, RMPB44 identified as Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus thuringiensis, Paenibacillus favisporus, Bacillus subtilis based on 16S rDNA gene sequence were used to study the effect of inoculation on growth, osmolytes, antioxidant status. Inoculation increased plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability, decreasing leaf water loss. Bacillus spp. effect on osmoregulation increased proline, sugars, free amino acids and decreased electrolyte leakage. Inoculation reduced the activity of antioxidant enzymes asc...
455 citations
TL;DR: Observations support the claim that implementation of the ‘high‐dose/refuge’ IRM strategy has been successful in substantially delaying field resistance to Bt crops.
Abstract: Transgenic maize and cotton expressing Bacillus thuringiensis (Bt) toxins were first commercialized in 1996. By 2009, Bt crops were planted on ca. 47.6 Mha in 22 countries worldwide, with the USA and Canada accounting for 54% of this area. Resistance (virulence) development in target insect pests is a major threat to the sustainable use of Bt crops. Four major target pests of Bt crops in the USA and Canada – European corn borer, Ostrinia nubilalis (Hubner), southwestern corn borer, Diatraea grandiosella Dyar (both Lepidoptera: Crambidae), tobacco budworm, Heliothis virescens Fabricius (Lepidoptera: Noctuidae), and pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) – remain susceptible to Bt toxins after 15 years of intensive use of Bt maize and Bt cotton. The success in sustaining susceptibility in these major pests is associated with successful implementation of the ‘high-dose/refuge’ insecticide resistance management (IRM) strategy: (i) Bt crop cultivars express a ‘high dose’, (ii) initial frequency of resistance alleles is very low, and (iii) a refuge is maintained nearby in the environment. Field resistance (including control failure) to a Bt crop has been clearly documented in three situations: fall armyworm [Spodoptera frugiperda JE Smith] in Puerto Rico, African stem borer [Busseola fusca Fuller (Lepidoptera: Noctuidae)] in South Africa, and P. gossypiella in India. Factors associated with these cases of field resistance include: failure to use high-dose Bt cultivars and lack of sufficient refuge. These observations support the claim that implementation of the ‘high-dose/refuge’ IRM strategy has been successful in substantially delaying field resistance to Bt crops.
254 citations
TL;DR: Genetic mapping of a membrane transporter (ABCC2) to a locus controlling Bt Cry1Ac toxin resistance in two lepidopterans implies that this protein plays a critical role in Bt function.
Abstract: Despite the prominent and worldwide use of Bacillus thuringiensis (Bt) insecticidal toxins in agriculture, knowledge of the mechanism by which they kill pests remains incomplete. Here we report genetic mapping of a membrane transporter (ABCC2) to a locus controlling Bt Cry1Ac toxin resistance in two lepidopterans, implying that this protein plays a critical role in Bt function.
246 citations
TL;DR: It is reported that the resistance to the Bt toxin Cry1Ac in the cabbage looper, Trichoplusia ni, evolved in greenhouses, is associated with differential alteration of two midgut aminopeptidases N, APN1 and APN6, conferred by a trans-regulatory mechanism.
Abstract: The soil bacterium Bacillus thuringiensis (Bt) is the most successfully used biopesticide in agriculture, and its insecticidal protein genes are the primary transgenes used for insect control in transgenic crops. However, evolution of insect resistance to Bt toxins threatens the long-term future of Bt applications. To date, cases of resistance to Bt toxins have been reported in agricultural situations in six insect species, but the molecular basis for these cases of resistance remains unclear. Here we report that the resistance to the Bt toxin Cry1Ac in the cabbage looper, Trichoplusia ni, evolved in greenhouses, is associated with differential alteration of two midgut aminopeptidases N, APN1 and APN6, conferred by a trans-regulatory mechanism. Biochemical, proteomic, and molecular analyses showed that in the Cry1Ac-resistant T. ni, APN1 was significantly down-regulated, whereas APN6 was significantly up-regulated. The Cry1Ac resistance was correlated with down-regulation of APN1 but not with the up-regulation of APN6. The concurrent up-regulation of APN6 and down-regulation of APN1 might play a role in compensating for the loss of APN1 to minimize the fitness costs of the resistance. Along with identifying reduced expression of APN1 as the molecular basis of Bt resistance selected in an agricultural setting, our findings demonstrate the importance of APN1 to the mode of action of Bt toxin Cry1Ac.
180 citations
TL;DR: The results have shown that the impact of T. absoluta can be greatly reduced by spraying only B. thuringiensis-based formulates, with no need for chemical insecticides, and the integration of this technology with other biological control methods focused on T. Absoluta eggs, such as the use of mirid predators or parasitoids.
Abstract: The tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is considered to be one of the most devastating pests affecting tomato crops in South America, where crop losses range from 60 to 100%. After its detection in the Spanish tomato-growing area at the end of 2006, it spread quickly to other European and northern African countries. Currently, T. absoluta management in these countries is mainly based on chemical treatments. Nonetheless, special emphasis is being placed on implementing environmentally safe strategies. Commercial formulates based on Bacillus thuringiensis may be a good alternative, as they have been used to control other insect pests successfully. The laboratory, greenhouse, and open-field experiments presented in this work are evidence that B. thuringiensis is highly efficient in controlling T. absoluta. First instar larvae were the most susceptible, while susceptibility was lower in second and third instar larvae. Our results have shown that the impact of T. absoluta can be greatly reduced by spraying only B. thuringiensis-based formulates, with no need for chemical insecticides. Furthermore, the integration of this technology with other biological control methods focused on T. absoluta eggs, such as the use of mirid predators or parasitoids, could reduce the number of B. thuringiensis treatments and the use of chemicals, with the consequent reduction of residues on fruits.
158 citations
TL;DR: Responsibility to Cry1Ac was significantly lower in 13 field populations from northern China, where Bt cotton has been planted intensively, than in two populations from sites in northwestern China where exposure to Bt Cotton has been limited, implying that resistance toCry1Ac in northern China is a specific adaptation caused by exposure to this toxin in Btotton.
Abstract: Transgenic crops producing Bacillus thuringiensis (Bt) toxins kill some key insect pests, but evolution of resistance by pests can reduce their efficacy. The predominant strategy for delaying pest resistance to Bt crops requires refuges of non-Bt host plants to promote survival of susceptible pests. To delay pest resistance to transgenic cotton producing Bt toxin Cry1Ac, farmers in the United States and Australia planted refuges of non-Bt cotton, while farmers in China have relied on “natural” refuges of non-Bt host plants other than cotton. Here we report data from a 2010 survey showing field-evolved resistance to Cry1Ac of the major target pest, cotton bollworm (Helicoverpa armigera), in northern China. Laboratory bioassay results show that susceptibility to Cry1Ac was significantly lower in 13 field populations from northern China, where Bt cotton has been planted intensively, than in two populations from sites in northwestern China where exposure to Bt cotton has been limited. Susceptibility to Bt toxin Cry2Ab did not differ between northern and northwestern China, demonstrating that resistance to Cry1Ac did not cause cross-resistance to Cry2Ab, and implying that resistance to Cry1Ac in northern China is a specific adaptation caused by exposure to this toxin in Bt cotton. Despite the resistance detected in laboratory bioassays, control failures of Bt cotton have not been reported in China. This early warning may spur proactive countermeasures, including a switch to transgenic cotton producing two or more toxins distinct from Cry1A toxins.
157 citations
TL;DR: The proteomic and genomic detection of reduced levels of midgut membrane-bound alkaline phosphatase (mALP) as a common feature in strains of Cry-resistant Heliothis virescens, Helicoverpa armigera and Spodoptera frugiperda when compared to susceptible larvae is reported.
Abstract: Development of insect resistance is one of the main concerns with the use of transgenic crops expressing Cry toxins from the bacterium Bacillus thuringiensis. Identification of biomarkers would assist in the development of sensitive DNA-based methods to monitor evolution of resistance to Bt toxins in natural populations. We report on the proteomic and genomic detection of reduced levels of midgut membrane-bound alkaline phosphatase (mALP) as a common feature in strains of Cry-resistant Heliothis virescens, Helicoverpa armigera and Spodoptera frugiperda when compared to susceptible larvae. Reduced levels of H. virescens mALP protein (HvmALP) were detected by two dimensional differential in-gel electrophoresis (2D-DIGE) analysis in Cry-resistant compared to susceptible larvae, further supported by alkaline phosphatase activity assays and Western blotting. Through quantitative real-time polymerase chain reaction (qRT-PCR) we demonstrate that the reduction in HvmALP protein levels in resistant larvae are the result of reduced transcript amounts. Similar reductions in ALP activity and mALP transcript levels were also detected for a Cry1Ac-resistant strain of H. armigera and field-derived strains of S. frugiperda resistant to Cry1Fa. Considering the unique resistance and cross-resistance phenotypes of the insect strains used in this work, our data suggest that reduced mALP expression should be targeted for development of effective biomarkers for resistance to Cry toxins in lepidopteran pests.
154 citations
TL;DR: This review is an attempt to provide an overview of the major trends and developments of Bt for the control of agricultural insect pests and to describe the main approaches that have been used to improve this natural bioinsecticide.
Abstract: Bacillus thuringiensis, known as Bt, is a spore-forming bacterium that occurs naturally in soil and that produces highly specific insecticidal proteins called Cry proteins. These proteins are stomach poisons that specifically affect insects. Today, Bt preparations are considered as the most effective, specific and environmentally-friendly bioinsecticides; they have been used as biological pesticides in agriculture, forestry and in human health for the elimination of vectors of diseases for more than 60 years and their implementation far exceeds other microbial agents such as fungi, protozoa or viruses. This review on the use of this entomopathogenic bacterium in crop protection is not intended to be a compilation of the results of all the investigations made in this field. Instead, it is an attempt to provide an overview of the major trends and developments of Bt for the control of agricultural insect pests and to describe the main approaches that have been used to improve this natural bioinsecticide. Bt-based insecticides are considered safe for mammals and birds, and are safer for non-target insects than conventional insecticides; they have become the most widely used microbial insecticides. However, Bt products have several limitations, such as a narrow activity spectrum, instability in rain and sunlight, and inefficiency against pest feeding on internal tissues of the plants. The first step towards improving Bt has involved the isolation of new strains with higher and broader insecticidal activity against targeted insect pests and the cloning of cry genes encoding new insecticidal crystal proteins. A second strategy was to increase the persistence of its toxins in the field by encapsulation in recombinant asporogenic Bt strains or other heterologous recombinant microbial hosts; this protected the toxins against UV degradation and had the advantage that the transgenic microorganisms released into the environment were non-viable. Bt has also become a key source of genes for transgenic expression to provide pest resistance in plants and in so-called genetically modified plants. The engineering of plants to express Bt cry genes has been especially helpful against pests that attack parts of the plant that are usually not well protected by conventional insecticide application. The potential effects on human health and the environment of the large-scale use of these Bt crops are also in the scope of this review.
TL;DR: Evidence is reported from five major crop pests refuting the hypothesis that genetically modified Bt toxins would be effective only if resistance was linked with mutations in genes encoding toxin-binding cadherin proteins.
Abstract: Transgenic crops that produce Bacillus thuringiensis (Bt) toxins are grown widely for pest control, but insect adaptation can reduce their efficacy. The genetically modified Bt toxins Cry1AbMod and Cry1AcMod were designed to counter insect resistance to native Bt toxins Cry1Ab and Cry1Ac. Previous results suggested that the modified toxins would be effective only if resistance was linked with mutations in genes encoding toxin-binding cadherin proteins. Here we report evidence from five major crop pests refuting this hypothesis. Relative to native toxins, the potency of modified toxins was >350-fold higher against resistant strains of Plutella xylostella and Ostrinia nubilalis in which resistance was not linked with cadherin mutations. Conversely, the modified toxins provided little or no advantage against some resistant strains of three other pests with altered cadherin. Independent of the presence of cadherin mutations, the relative potency of the modified toxins was generally higher against the most resistant strains.
TL;DR: It is demonstrated that E. faecalis is a commensal in the gut of Manduca sexta and a pathogen in the hemocoel, resulting in a robust immune response and rapid death, a process the authors refer to as the “commensal-to-pathogen” switch.
Abstract: A dynamic homeostasis is maintained between the host and native bacteria of the gastrointestinal tract in animals, but migration of bacteria from the gut to other organs can lead to disease or death. Enterococcus faecalis is a commensal of the gastrointestinal tract; however, Enterococcus spp. are increasingly frequent causes of nosocomial infections with a high mortality rate. We investigated the commensal-to-pathogen switch undergone by E. faecalis OG1RF in the lepidopteran model host Manduca sexta associated with its location in the host. E. faecalis persists in the harsh midgut environment of M. sexta larvae without causing apparent illness, but injection of E. faecalis directly into the larval hemocoel is followed by rapid death. Additionally, oral ingestion of E. faecalis in the presence of Bacillus thuringiensis insecticidal toxin, a pore-forming toxin that targets the midgut epithelium, induces an elevated mortality rate. We show that the loss of gut integrity due to B. thuringiensis toxin correlates with the translocation of E. faecalis from the gastrointestinal tract into the hemolymph. Upon gaining access to the hemolymph, E. faecalis induces an innate immune response, illustrated by hemocyte aggregation, in larvae prior to death. The degree of hemocyte aggregation is dependent upon the route of E. faecalis entry. Our data demonstrate the efficacy of the M. sexta larval model system in investigating E. faecalis-induced sepsis and clarifies controversies in the field regarding the events leading to larval death following B. thuringiensis toxin exposure. IMPORTANCE This study advances our knowledge of Enterococcus faecalis-induced sepsis following translocation from the gut and provides a model for mammalian diseases in which the spatial distribution of bacteria determines disease outcomes. We demonstrate that E. faecalis is a commensal in the gut of Manduca sexta and a pathogen in the hemocoel, resulting in a robust immune response and rapid death, a process we refer to as the “commensal-to-pathogen” switch. While controversy remains regarding Bacillus thuringiensis toxin-induced killing, our laboratory previously found that under some conditions, the midgut microbiota is essential for B. thuringiensis toxin killing of Lymantria dispar (N. A. Broderick, K. F. Raffa, and J. Handelsman, Proc. Natl. Acad. Sci. U. S. A. 103:15196–15199, 2006; B. Raymond, et al., Environ. Microbiol. 11:2556–2563, 2009; P. R. Johnston, and N. Crickmore, Appl. Environ. Microbiol. 75:5094–5099, 2009). We and others have demonstrated that the role of the midgut microbiota in B. thuringiensis toxin killing is dependent upon the lepidopteran species and formulation of B. thuringiensis toxin (N. A. Broderick, K. F. Raffa, and J. Handelsman, Proc. Natl. Acad. Sci. U. S. A. 103:15196–15199, 2006; N. A. Broderick, et al., BMC Biol. 7:11, 2009). This work reconciles much of the apparently contradictory previous data and reveals that the M. sexta-E. faecalis system provides a model for mammalian sepsis.
TL;DR: Results demonstrate that when B. thuringiensis treatments are applied immediately after the initial detection of T. absoluta on plants, they do not interfere with N. tenuis establishment in the crop because T.Absoluta eggs are available, and treatments with B.Thuringienis later in the growing season would no longer be necessary because mirids alone would control the pest.
Abstract: Since Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) was first detected at the end of 2006 in the Mediterranean Basin, several endemic natural enemies have been reported to prey on this exotic pest. The predator Nesidiocoris tenuis Reuter (Hemiptera: Miridae) can regulate T. absoluta populations, because it is able to prey efficiently on T. absoluta eggs. Furthermore, previous studies have demonstrated that first-instar larvae of T. absoluta are highly susceptible to Bacillus thuringiensis (Bt) treatments. In this work, we tested the combination of both approaches under greenhouse conditions. B. thuringiensis formulations were sprayed weekly for two months, three months or throughout the growing cycle, and in all cases, one N. tenuis per plant was also released. Control plants were completely destroyed by the infestation levels reached by T. absoluta. In contrast, all treatments based on B. thuringiensis treatments and releases of N. tenuis reduced leaf damage by more than 97% when compared to the untreated control, with no significant differences among them. Furthermore, yield in the control plants was significantly reduced when compared with all Bt–N. tenuis treatments. Our results demonstrate that when B. thuringiensis treatments are applied immediately after the initial detection of T. absoluta on plants, they do not interfere with N. tenuis establishment in the crop because T. absoluta eggs are available. According to our data, treatments with B. thuringiensis later in the growing season would no longer be necessary because mirids alone would control the pest.
TL;DR: The specific binding of Cry2Ae toxin to binding sites on BBMV from larvae of the three most commercially relevant heliothine species, Heliothis virescens, Helicoverpa zea, and Helic overpa armigera is reported.
Abstract: The use of combinations of Bacillus thuringiensis (Bt) toxins with diverse modes of action for insect pest control has been proposed as the most efficient strategy to increase target range and delay the onset of insect resistance. Considering that most cases of cross-resistance to Bt toxins in laboratory-selected insect colonies are due to alteration of common toxin binding sites, independent modes of action can be defined as toxins sharing limited or no binding sites in brush border membrane vesicles (BBMV) prepared from the target insect larvae. In this paper, we report on the specific binding of Cry2Ae toxin to binding sites on BBMV from larvae of the three most commercially relevant heliothine species, Heliothis virescens, Helicoverpa zea, and Helicoverpa armigera. Using chromatographic purification under reducing conditions before labeling, we detected specific binding of radiolabeled Cry2Ae, which allowed us to perform competition assays using Cry1Ab, Cry1Ac, Cry1Fa, Vip3A, Cry2Ae, and Cry2Ab toxins as competitors. In these assays, Cry2Ae binding sites were shared with Cry2Ab but not with the tested Cry1 or Vip3A toxins. Our data support the use of Cry2Ae toxin in combination with Cry1 or Vip3A toxins in strategies to increase target range and delay the onset of heliothine resistance.
TL;DR: RPW hemocytes, the main immunocompetent cells in the insect, are described for the first time and the hemocyte response of RPW larvae to sub-lethal doses of commercial products containing Bt was examined.
TL;DR: The present study briefly summarizes the data regarding the development and commercial use of transgenic Bt varieties, elaborate on the procedure and methods for assessing the non-target effects of insect-resistant GE plants, and synthetically analyze the related research results.
Abstract: The application of recombinant DNA technology has resulted in many insect-resistant varieties by genetic engineering (GE). Crops expressing Cry toxins derived from Bacillus thuringiensis (Bt) have been planted worldwide, and are an effective tool for pest control. However, one ecological concern regarding the potential effects of insect-resistant GE plants on non-target organisms (NTOs) has been continually debated. In the present study, we briefly summarize the data regarding the development and commercial use of transgenic Bt varieties, elaborate on the procedure and methods for assessing the non-target effects of insect-resistant GE plants, and synthetically analyze the related research results, mostly those published between 2005 and 2010. A mass of laboratory and field studies have shown that the currently available Bt crops have no direct detrimental effects on NTOs due to their narrow spectrum of activity, and Bt crops are increasing the abundance of some beneficial insects and improving the natural control of specific pests. The use of Bt crops, such as Bt maize and Bt cotton, results in significant reductions of insecticide application and clear benefits on the environment and farmer health. Consequently, Bt crops can be a useful component of integrated pest management systems to protect the crop from targeted pests.
TL;DR: The midgut histopathology of Vip3Aa fed larvae showed vacuolization of the cytoplasm, brush border membrane destruction, vesicle formation in the apical region and cellular disintegration, which supports the use of VIP3AA16 proteins as insecticidal agent, especially in case of Cry-resistance management.
TL;DR: The results have shown the significance of pyramiding and co-expression of two Cry toxins for efficient protection against lepidopteran pests of chickpea.
Abstract: The modified cry1Ab and cry1Ac insecticidal genes of Bacillus thuringiensis (Bt) under the control of two different constitutive promoters have been introduced into chickpea (Cicer arietinum L.) by Agrobacterium-mediated transformation of pre-conditioned cotyledonary nodes. 118 stable transformed T0 plants as independent transformation events were obtained expressing individual cry1Ab, cry1Ac or both pyramided genes for their co-expression driven by either cauliflower mosaic virus 35S promoter with duplicated enhancer (CaMV35S) or synthetic constitutive promoter (Pcec) and their combinations. Integration and inheritance of transgenes in T0 and T1 population of transgenic chickpea plants were determined by PCR, RT-PCR and Southern hybridization. Results of Southern hybridization showed single copy integration of cry1Ab or cry1Ac genes in most of the transgenic plants developed with either single or pyramided genes and reflected Mendelian inheritance of transgenes in T1 progeny. Real time PCR of pyramided transgenic plants clearly showed differential expression of transcripts for both the genes driven by CaMV35S and Pcec promoters. Quantitative assessment of Bt Cry toxins by ELISA of T0 transgenic chickpea plants showed expression of toxin ranging from 5 to 40 ng mg−1 of total soluble protein (TSP) in leaves of transgenic plants. Insect bioassay performed with transgenic plants showed relatively higher toxicity for plants expressing Cry1Ac protein as compared to Cry1Ab to Helicoverpa armigera. Pyramided transgenic plants with moderate expression levels (15–20 ng mg−1 of TSP) showed high-level of resistance and protection against pod borer larvae of H. armigera as compared to high level expression of a single toxin. These results have shown the significance of pyramiding and co-expression of two Cry toxins for efficient protection against lepidopteran pests of chickpea.
TL;DR: Results suggest methanol extracts of J. curcas and B. thuringiensis israelensis have potential to be used as an ideal eco-friendly approach for the control of the major lymphatic filarial vector, C. quinquefasciatus.
Abstract: The present study explored the effects of Jatropha curcas leaf extract and Bacillus thuringiensis israelensis larvicidal activity against the lymphatic filarial vector, Culex quinquefasciatus. Wights were selected for investigating the larvicidal potential against the first to fourth instar larvae of the laboratory-reared mosquito species, C. quinquefasciatus Say, in which the major lymphatic filariasis was used. The medicinal plants were collected from the area around Bharathiar University, Coimbatore. The dried plant materials were powdered by an electric blender. From the powder, 100 g of the plant materials was extracted with 300 ml of organic solvents of methanol for 8 h, using a Soxhlet apparatus, and filtered. The crude plant extracts were evaporated to dryness in a rotary vacuum evaporator. The plant extract showed larvicidal effects after 24 h of exposure; however, the highest larval mortality was found in the leaf extract of methanol J. curcas against the first to fourth instar larvae of values LC50 = 1.200%, 1.290%, 1.358%, and 1.448% and LC90 = 2.094%, 2.323%, 2.444%, and 2.544% and B. thuringiensis israelensis against the first to fourth instar larvae of values LC50 = 9.332%, 9.832%, 10.212%, 10.622% and LC90 = 15.225%, 15.508%, 15.887%, and 15.986% larvae of C. quinquefasciatus, respectively. No mortality was observed in the control. These results suggest methanol extracts of J. curcas and B. thuringiensis israelensis have potential to be used as an ideal eco-friendly approach for the control of the major lymphatic filarial vector, C. quinquefasciatus.
TL;DR: Cry1Ab has limited effects on fall armyworm; whereas Cry1F demonstrated significant reductions in foliar injury and lower survivorship compared to that on non-Bt corn tissues, suggesting selection pressures across the farmscape could be affected.
TL;DR: This is the first report among the non-photosynthetic microbes, where the Bacillus spp.—B.
Abstract: Metabolic activities of four Bacillus strains to transform glucose into hydrogen (H2) and polyhydroxybutyrate (PHB) in two stages were investigated in this study. Under batch culture conditions, Bacillus thuringiensis EGU45 and Bacillus cereus EGU44 evolved 1.67–1.92 mol H2/mol glucose, respectively during the initial 3 days of incubation at 37°C. In the next 2 days, the residual glucose solutions along with B. thuringiensis EGU45 shaken at 200 rpm was found to produce PHB yield of 11.3% of dry cell mass. This is the first report among the non-photosynthetic microbes, where the Bacillus spp.—B. thuringiensis and B. cereus strains have been shown to produce H2 and PHB in same medium under different conditions.
TL;DR: Cry4Ba domain II loop α-8 is involved in binding and in synergism with Cyt1Aa since Cry4Ba SI303-304AA double mutant showed decreased binding and synergismwith Cyt2Aa, suggesting the mechanism of synergism between these two Bti toxins is similar to that of Cry11Aa and Cyt 1Aa.
TL;DR: The data indicate that cultivation of MIR162 maize poses negligible risk to non-target organisms, and that crops producing Vip3A are unlikely to adversely affect biological control organisms such that benefits from reduced insecticide applications are lost.
Abstract: Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) provide economic, environmental and health benefits by maintaining or increasing crop yields with fewer applications of insecticide. To sustain these benefits, it is important to delay the evolution of insect resistance to the proteins, and to ensure that the proteins do not harm non-target organisms, particularly those that may control secondary pests that would otherwise flourish because of reduced insecticide applications. Vip3A is a Bt vegetative insecticidal protein that is active against lepidopterous pests. It has a different mode of action from other proteins for control of Lepidoptera in current Bt crops, and when combined with these proteins, it should help to delay the evolution of pest resistance to Bt crops. This paper presents data on the effects of Vip3A on non-target organisms, and an ecological risk assessment of MIR162 maize, which expresses Vip3Aa20. Laboratory studies indicate few adverse effects of Vip3A to non-target organisms: 11 of 12 species tested showed no adverse effects when exposed to high concentrations of Vip3A relative to estimated exposures resulting from cultivation of MIR162 maize. Daphnia magna exposed to Vip3Aa20 were unaffected in terms of survival or fecundity, but grew slightly more slowly than unexposed controls. The data indicate that cultivation of MIR162 maize poses negligible risk to non-target organisms, and that crops producing Vip3A are unlikely to adversely affect biological control organisms such that benefits from reduced insecticide applications are lost.
TL;DR: It is demonstrated that Bt cotton will pose a negligible risk to C. maculata and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Btotton, thus demonstrating a comprehensive system for assessing the risk of genetically modified plants on non-target organisms.
Abstract: The ladybird beetle, Coleomegilla maculata (DeGeer), is a common and abundant predator in many cropping systems. Its larvae and adults are predaceous, feeding on aphids, thrips, lepidopteran larvae and plant tissues, such as pollen. Therefore, this species is exposed to insecticidal proteins expressed in insect-resistant, genetically engineered cotton expressing Cry proteins derived from Bacillus thuringiensis (Bt). A tritrophic bioassay was conduced to evaluate the potential impact of Cry2Ab- and Cry1Ac-expressing cotton on fitness parameters of C. maculata using Bt-susceptible and -resistant larvae of Trichoplusia ni as prey. Coleomegilla maculata survival, development time, adult weight and fecundity were not different when they were fed with resistant T. ni larvae reared on either Bt or control cotton. To ensure that C. maculata were not sensitive to the tested Cry toxins independent from the plant background and to add certainty to the hazard assessment, C. maculata larvae were fed artificial diet incorporated with Cry2Ab, Cry1Ac or both at >10 times higher concentrations than in cotton tissue. Artificial diet containing E-64 was included as a positive control. No differences were detected in any life-table parameters between Cry protein-containing diet treatments and the control diet. In contrast, larvae of C. maculata fed the E-64 could not develop to the pupal stage and the 7-d larval weight was significantly negatively affected. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources were confirmed by ELISA and sensitive-insect bioassays. Our results show that C. maculata is not affected by Bt cotton and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Bt cotton, thus demonstrating that Bt cotton will pose a negligible risk to C. maculata. More importantly, this study demonstrates a comprehensive system for assessing the risk of genetically modified plants on non-target organisms.
TL;DR: Several isolates of Bacillus thuringiensis showed promising results, and upon purification the aphidicidal protein was recognized as a binary toxin, and holds a promise of its use in future as a candidate gene for developing transgenic crop plants tolerant against sap-sucking insect pests.
Abstract: Several isolates of Bacillus thuringiensis (Bt) were screened for the vegetative insecticidal protein (Vip) effective against sap-sucking insect pests. Screening results were based on LC(50) values against cotton aphid (Aphis gossypii), one of the dangerous pests of various crop plants including cotton. Among the isolates, the Bt#BREF24 showed promising results, and upon purification the aphidicidal protein was recognized as a binary toxin. One of the components of this binary toxin was identified by peptide sequencing to be a homolog of Vip2A that has been reported previously in other Bacillus spp. Vip2 belongs to the binary toxin group Vip1-Vip2, and is responsible for the enzymatic activity; and Vip1 is the translocation and receptor binding protein. The two genes encoding the corresponding proteins of the binary toxin, designated as vip2Ae and vip1Ae, were cloned from the Bt#BREF24, sequenced, and heterologously expressed in Escherichia coli. Aphid feeding assay with the recombinant proteins confirmed that these proteins are indeed the two components of the binary toxins, and the presence of both partners is essential for the activity. Aphid specificity of the binary toxin was further verified by ligand blotting experiment, which identified an ~50 kDa receptor in the brush border membrane vesicles of the cotton aphids only, but not in the lepidopteran insects. Our finding holds a promise of its use in future as a candidate gene for developing transgenic crop plants tolerant against sap-sucking insect pests.
TL;DR: It is demonstrated that the two-gene lines of insect-resistant rice expressing two Bt genes have commercial potential and could serve as a valuable IRM strategy.
Abstract: BACKGROUND: Transgenic crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis Berliner (Bt )w ere first commercialised in 1996. The risk that pests have the potential to evolve resistance to Bt toxins is one of the most serious challenges to this technology. Gene stacking, pyramiding two Bt genes into one variety, is considered to be an effective insect resistance management (IRM) strategy. In this study, insect-resistant rice expressing two Bt genes was developed by sexual crossing, and then characterised. RESULTS: Homozygous rice lines of two pyramided Bt genes were obtained in the F3 generation. Quantification of Bt toxin showedthatproteinconcentrationsofCry1Ab,Cry1AcandCry2Ainthetwo-genelineswerecomparablewiththeirsingle-gene parents, while the expression of cry1C gene decreased after gene stacking. Four two-gene lines showed higher activity to striped stem borer (Chilo suppressalis Walker) than parental lines in the laboratory bioassay. All pyramided lines and their hybrids exhibited excellent efficacy against stemborers and leaffolders in field evaluation, while most pyramided lines had no significant differences from original variety in yield under spraying of insecticide. CONCLUSION: These results demonstrate that the two-gene lines have commercial potential and could serve as a valuable IRM strategy. c � 2011 Society of Chemical Industry
TL;DR: Results demonstrate that the step of activation, mainly, is at the origin of the difference of susceptibility of these two larvae towards B. thuringiensis Vip3Aa16 toxin.
TL;DR: This is the first systematic examination of the physiological basis for the low efficacy of Cry toxins against aphids, and analysis of Cry toxin-aphid gut interaction.
TL;DR: Cry1Ab resistance in D. saccharalis was incompletely dominant on commercial Bt corn hybrids, however, both experimental lines with pyramided genes of Cry1A.105 and Cry2Ab2 provided complete control of all three insect genotypes in both leaf tissue and intact plant tests.