Bacillus Thuringiensis (bacillus + thuringiensi)

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Terms modified by Bacillus Thuringiensis

  • bacillus thuringiensi strain

  • Selected Abstracts

    Could Bt transgenic crops have nutritionally favourable effects on resistant insects?

    ECOLOGY LETTERS, Issue 3 2003
    Ali H. Sayyed
    Abstract We present an idea that larvae of some Bacillus thuringiensis (Bt,) resistant populations of the diamondback moth, Plutella xylostella (L.), may be able to use Cry1Ac toxin derived from Bt as a supplementary food protein. Bt transgenic crops could therefore have unanticipated nutritionally favourable effects, increasing the fitness of resistant populations. This idea is discussed in the context of the evolution of resistance to Bt transgenic crops. [source]

    Evaluation of dietary effects of transgenic corn pollen expressing Cry3Bb1 protein on a non-target ladybird beetle, Coleomegilla maculata

    Jian J. Duan
    Abstract A transgenic corn event (MON 863) has been recently developed by Monsanto Company for control of corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae). This transgenic corn event expresses the cry3Bb1 gene derived from Bacillus thuringiensis (Berliner), which encodes the insecticidal Cry3Bb1 protein for corn rootworm control. A continuous feeding study was conducted in the laboratory to evaluate the dietary effect of MON 863 pollen expressing the Cry3Bb1 protein on the survival, larval development, and reproductive capacity of the non-target species, Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae). First instar C. maculata (less than 24 h old) and newly emerging adults (less than 72 h old) were fed individually on a diet mixture containing 50% of MON 863 pollen, non-transgenic (control) corn pollen, bee pollen (a component of normal rearing diet), or potassium arsenate-treated control corn pollen. In the larval tests, 96.7%, 90.0%, and 93.3% of C. maculata larvae successfully pupated and then emerged as adults when fed on MON 863 pollen, non-transgenic corn pollen, and bee pollen (normal rearing) diets, respectively. Among the larvae completing their development, there were no significant differences in the developmental time to pupation and adult emergence among the transgenic corn pollen, non-transgenic corn pollen, and bee pollen diet treatments. All larvae fed on arsenate treated corn pollen diet died as larvae. For tests with adults, 83.3%, 80.0%, and 100% of adult C. maculata survived for the 30 days of the test period when reared on diets containing 50% of MON 863 pollen, non-transgenic corn pollen, and bee pollen respectively. While the adult survival rate on MON 863 pollen diet was significantly less than that on the bee pollen diet, there was no significant difference between the MON 863 and non-transgenic corn pollen treatments. During the period of adult testing, an average of 77, 80, and 89 eggs per female were laid by females fed on the MON 863 pollen, control corn pollen, and bee pollen, respectively; no significant differences were detected in the number of eggs laid among these treatments. These results demonstrate that when offered at 50% by weight of the dietary component, transgenic corn (MON 863) pollen expressing Cry3Bb1 protein had no measurable negative effect on the survival and development of C. maculata larvae to pupation and adulthood nor any adverse effect on adult survival and reproductive capacity. Relevance of these findings to ecological impacts of transgenic Bt crops on non-target beneficial insects is discussed. [source]

    Effect of rice lines transformed with Bacillus thuringiensis toxin genes on the brown planthopper and its predator Cyrtorhinus lividipennis

    Carmencita C. Bernal
    Abstract Five transgenic rice lines, each containing an insecticidal toxin gene from Bacillus thuringiensis (Bt) under control of a different promoter, were tested for effects on two non-target insects: the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and its predator Cyrtorhinus lividipennis (Hemiptera: Miridae). Bt toxin was detected by ELISA in the honeydew of N. lugens that fed on rice lines with the CaMV 35S and actin promoters. Nilaparvata lugens produced greater volumes of acidic honeydew (derived from xylem feeding) on all five Bt rice lines than on non-transgenic control lines. The amount of honeydew derived from phloem feeding did not differ between Bt and control lines. There were no differences between N. lugens reared on Bt and control lines in any of the five fitness parameters measured (survival to the adult stage, male and female weight, and male and female developmental time). There were no differences between C. lividipennis reared on N. lugens nymphs from Bt and control lines, in any of the three fitness parameters examined (survival to the adult stage and male and female developmental time). Our results indicate that N. lugens and its natural enemies will be exposed to Bt toxins from rice lines transformed with some Bt gene constructs, but that this exposure might not affect N. lugens and C. lividipennis fitness. [source]

    Insecticidal effects of selected biological control agents on the larvae of Plutella xylostella (Lepidoptera: Plutellidae)

    Ömer ERTÜRK
    Abstract To identify a more effective and safe biological control agent against a common cabbage pest, Plutella xylostella (L.) (Lepidoptera: Plutellidae), the insecticidal effects of selected biological agents were evaluated. The highest insecticidal effects determined were 100, 73.5, 45.5, 47 and 55.3% using toxin HD-1 (isolated from the Harry Dumagae strain of Bacillus thuringiensis), toxin BTS-1 (isolated from the tenebrionis strain of B. thuringiensis), B. thuringiensis Berliner, B. thuringiensis israelensis and B. thuringiensis kurstaki, respectively. [source]

    Distribution of S-layers on the surface of Bacillus cereus strains: phylogenetic origin and ecological pressure

    Tâm Mignot
    Bacillus anthracis, Bacillus cereus and Bacillus thuringiensis have been described as members of the Bacillus cereus group but are, in fact, one species. B. anthracis is a mammal pathogen, B. thuringiensis an entomopathogen and B. cereus a ubiquitous soil bacterium and an occasional human pathogen. In two clinical isolates of B. cereus, in some B. thuringiensis strains and in B. anthracis, an S-layer has been described. We investigated how the S-layer is distributed in B. cereus, and whether phylogeny or ecology could explain its presence on the surface of some but not all strains. We first developed a simple biochemical assay to test for the presence of the S-layer. We then used the assay with 51 strains of known genetic relationship: 26 genetically diverse B. cereus and 25 non- B. anthracis of the B. anthracis cluster. When present, the genetic organization of the S-layer locus was analysed further. It was identical in B. cereus and B. anthracis. Nineteen strains harboured an S-layer, 16 of which belonged to the B. anthracis cluster. All 19 were B. cereus clinical isolates or B. thuringiensis, except for one soil and one dairy strain. These findings suggest a common phylogenetic origin for the S-layer at the surface of B. cereus strains and, presumably, ecological pressure on its maintenance. [source]

    Subacute effects of transgenic Cry1Ab Bacillus thuringiensis corn litter on the isopods Trachelipus rathkii and Armadillidium nasatum

    Bryan W. Clark
    Abstract Laboratory studies were conducted to investigate the subacute effects of transgenic Cry1Ab corn leaf material containing Bacillus thuringiensis (Bt) protein on the terrestrial isopods Trachelipus rathkii and Armadillidium nasatum. Survival and growth were measured for eight weeks in isopods fed leaf material of two Bt11 corn varieties, two Monsanto 810 (Mon810) corn varieties, and the isolines of each. Total lipid and protein content of the organisms was measured to examine effects on energetic reserves. Armadillidium nasatum individuals in all treatments responded similarly. For T. rathkii, no statistically significant effect of Bt was observed, but statistical differences were observed in growth between hybrids. Protein and sugar content of the food were found to be correlated with the differences in growth for T. rathkii. Total protein content was higher in T. rathkii and A. nasatum fed material with higher protein and sugar content. A trend toward less growth in T. rathkii on Bt corn varieties versus their isolines triggered a concentration-response assay with purified Cry1Ab protein. No adverse effects of purified Bt protein were observed. These results indicate that little hazard to T. rathkii and A. nasatum from Bt corn leaf material from these hybrids exists. However, nutritional differences in corn hybrids contributed to differences in isopod growth. [source]

    Evolutionary ecology of insect adaptation to Bt crops

    Yves Carrière
    Abstract Transgenic crops producing Bacillus thuringiensis (Bt) toxins are used worldwide to control major pests of corn and cotton. Development of strategies to delay the evolution of pest resistance to Bt crops requires an understanding of factors affecting responses to natural selection, which include variation in survival on Bt crops, heritability of resistance, and fitness advantages associated with resistance mutations. The two main strategies adopted for delaying resistance are the refuge and pyramid strategies. Both can reduce heritability of resistance, but pyramids can also delay resistance by reducing genetic variation for resistance. Seasonal declines in the concentration of Bt toxins in transgenic cultivars, however, can increase the heritability of resistance. The fitness advantages associated with resistance mutations can be reduced by agronomic practices, including increasing refuge size, manipulating refuges to increase fitness costs, and manipulating Bt cultivars to reduce fitness of resistant individuals. Manipulating costs and fitness of resistant individuals on transgenic insecticidal crops may be especially important for thwarting evolution of resistance in haplodiploid and parthenogenetic pests. Field-evolved resistance to Bt crops in only five pests during the last 14 years suggests that the refuge strategy has successfully delayed resistance, but the accumulation of resistant pests could accelerate. [source]

    A new group of parasporal inclusions encoded by the S-layer gene of Bacillus thuringiensis

    Gang Guo
    Abstract Bacillus thuringiensis produces various groups of active proteins, such as Cyt, Vip and Parasporin, in addition to the Cry protein. In this study we show S-layer proteins to be a new group of parasporal inclusions of B. thuringiensis. The S-layer consists of a two-dimensional lattice structure and is the outermost component of many archaeobacteria and eubacteria. The parasporal inclusion of B. thuringiensis strain CTC was found to be not a typical crystal protein encoded by the cry gene, but a proteinaceous inclusion encoded by the S-layer gene. Furthermore, the CTC-like strains (with their parasporal inclusions coded by the S-layer gene) are widely distributed and accounted for 25.4% of the B. thuringiensis strains tested. These strains constitue a new group of parasporal inclusions encoded by the S-layer gene of B. thuringiensis and shed new light on B. thuringiensis nontoxic strains. [source]

    From soil to gut: Bacillus cereus and its food poisoning toxins

    Lotte P. Stenfors Arnesen
    Abstract Bacillus cereus is widespread in nature and frequently isolated from soil and growing plants, but it is also well adapted for growth in the intestinal tract of insects and mammals. From these habitats it is easily spread to foods, where it may cause an emetic or a diarrhoeal type of food-associated illness that is becoming increasingly important in the industrialized world. The emetic disease is a food intoxication caused by cereulide, a small ring-formed dodecadepsipeptide. Similar to the virulence determinants that distinguish Bacillus thuringiensis and Bacillus anthracis from B. cereus, the genetic determinants of cereulide are plasmid-borne. The diarrhoeal syndrome of B. cereus is an infection caused by vegetative cells, ingested as viable cells or spores, thought to produce protein enterotoxins in the small intestine. Three pore-forming cytotoxins have been associated with diarrhoeal disease: haemolysin BL (Hbl), nonhaemolytic enterotoxin (Nhe) and cytotoxin K. Hbl and Nhe are homologous three-component toxins, which appear to be related to the monooligomeric toxin cytolysin A found in Escherichia coli. This review will focus on the toxins associated with foodborne diseases frequently caused by B. cereus. The disease characteristics are described, and recent findings regarding the associated toxins are discussed, as well as the present knowledge on virulence regulation. [source]

    PCR-based identification of Bacillus thuringiensis pesticidal crystal genes

    Manuel Porcar
    Abstract The polymerase chain reaction (PCR) is a molecular tool widely used to characterize the insecticidal bacterium Bacillus thuringiensis. This technique can be used to amplify specific DNA fragments and thus to determine the presence or absence of a target gene. The identification of B. thuringiensis toxin genes by PCR can partially predict the insecticidal activity of a given strain. PCR has proven to be a rapid and reliable method and it has largely substituted bioassays in preliminary classification of B. thuringiensis collections. In this work, we compare the largest B. thuringiensis PCR-based screenings, and we review the natural occurrence of cry genes among native strains. We also discuss the use of PCR for the identification of novel cry genes, as well as the potential of novel technologies for the characterization of B. thuringiensis strains. [source]

    Isolation of transcripts from Diabrotica virgifera virgifera LeConte responsive to the Bacillus thuringiensis toxin Cry3Bb1

    A. Sayed
    Abstract Crystal (Cry) proteins derived from Bacillus thuringiensis (Bt) have been widely used as a method of insect pest management for several decades. In recent years, a transgenic corn expressing the Cry3Bb1 toxin has been successfully used for protection against corn rootworm larvae (genus Diabrotica). The biological action of the Bt toxin in corn rootworms has not yet been clearly defined. Because development of resistance to Bt by corn rootworms will have huge economic and ecological costs, insight into larval response to Bt toxin is highly desirable. We identified 19 unique transcripts that are differentially expressed in D. virgifera virgifera larvae reared on corn transgenic for Cry3Bb1. Putative identities of these genes were consistent with impacts on metabolism and development. Analysis of highly modulated transcripts resulted in the characterization of genes coding for a member of a cysteine-rich secretory protein family and a glutamine-rich membrane protein. A third gene that was isolated encodes a nondescript 132 amino acid protein while a fourth highly modulated transcript could not be further characterized. Expression patterns of these four genes were strikingly different between susceptible and resistant western corn rootworm populations. These genes may provide useful targets for monitoring of Bt exposure patterns and resistance development in pest and non-target insect populations. [source]

    Mining an Ostrinia nubilalis midgut expressed sequence tag (EST) library for candidate genes and single nucleotide polymorphisms (SNPs)

    B. S. Coates
    Abstract Genes expressed in lepidopteran midgut tissues are involved in digestion and Bacillus thuringiensis (Bt) toxin resistance traits. Five hundred and thirty five unique transcripts were annotated from 1745 high quality O. nubilalis larval midgut expressed sequence tags (ESTs). Full-length cDNA sequence of 12 putative serine proteinase genes and 3 partial O. nubilalis aminopeptidase N protein genes, apn1, apn3, and apn4, were obtained, and genes may have roles in plant feeding and Bt toxin resistance traits of Ostrinia larvae. The EST library was not normalized and insert frequencies reflect transcript levels under the initial treatment conditions and redundancy of inserts from highly expressed transcripts allowed prediction of putative single nucleotide polymorphisms (SNPs). Ten di-, tri- or tetranucleotide repeat unit microsatellite loci were identified, and minisatellite repeats were observed within the C-termini of two encoded serine proteinases. Molecular markers showed polymorphism at 28 SNP loci and one microsatellite locus, and Mendelian inheritance indicated that markers were applicable to genome mapping applications. This O. nubilalis larval midgut EST collection is a resource for gene discovery, expression information, and allelic variation for use in genetic marker development. [source]

    Sequence variation in trypsin- and chymotrypsin-like cDNAs from the midgut of Ostrinia nubilalis: methods for allelic differentiation of candidate Bacillus thuringiensis resistance genes

    B. S. Coates
    Abstract Midgut expressed alkaline serine proteases of Lepidoptera function in conversion of Bacillus thuringiensis (Bt) protoxin to active toxin, and reduced level of transcript T23 is associated with Ostrinia nubilalis resistance to Dipel® Bt formulations. Three groups of trypsin- (OnT25, OnT23, and OnT3) and two chymotrypsin-like (OnC1 and OnC2) cDNAs were isolated from O. nubilalis midgut tissue. Intraspecific groupings are based on cDNA similarity and peptide phylogeny. Derived serine proteases showed a catalytic triad (His, Asp, and Ser; except transcript OnT23a), three substrate specificity-determining residues, and three paired disulphide bonds. RT-PCR indicated all transcripts are expressed in the midgut. Mendelian-inherited genomic markers for loci OnT23, OnT3 and OnC1 will be useful for association of alleles with bioassayed Bt toxin resistance phenotypes. [source]

    Novel genetic basis of field-evolved resistance to Bt toxins in Plutella xylostella

    S. W. Baxter
    Abstract Insecticidal toxins from Bacillus thuringiensis (Bt) are widely used to control pest insects, but evolution of resistance threatens their continued efficacy. The most common type of Bt resistance (,Mode 1') is characterized by recessive inheritance, > 500-fold resistance to at least one Cry1A toxin, negligible cross-resistance to Cry1C, and reduced binding of Bt toxins to midgut membrane target sites. Mutations affecting a Cry1A-binding midgut cadherin protein are linked to laboratory-selected Mode 1 resistance in Heliothis virescens and Pectinophora gossypiella. Here we show that field-evolved Mode 1 resistance in the diamondback moth, Plutella xylostella, has a different genetic basis, indicating that screening for resistance in the field should not be restricted to a previously proposed DNA-based search for cadherin mutations. [source]

    cDNA sequence, mRNA expression and genomic DNA of trypsinogen from the Indianmeal moth, Plodia interpunctella

    Y. C. Zhu
    Abstract Trypsin-like enzymes are major insect gut enzymes that digest dietary proteins and proteolytically activate insecticidal proteins produced by the bacterium Bacillus thuringiensis (Bt). Resistance to Bt in a strain of the Indianmeal moth, Plodia interpunctella, was linked to the absence of a major trypsin-like proteinase (Oppert et al., 1997). In this study, trypsin-like proteinases, cDNA sequences, mRNA expression levels and genomic DNAs from Bt-susceptible and -resistant strains of the Indianmeal moth were compared. Proteinase activity blots of gut extracts indicated that the susceptible strain had two major trypsin-like proteinases, whereas the resistant strain had only one. Several trypsinogen-like cDNA clones were isolated and sequenced from cDNA libraries of both strains using a probe deduced from a conserved sequence for a serine proteinase active site. cDNAs of 852 nucleotides from the susceptible strain and 848 nucleotides from the resistant strain contained an open reading frame of 783 nucleotides which encoded a 261-amino acid trypsinogen-like protein. There was a single silent nucleotide difference between the two cDNAs in the open reading frame and the predicted amino acid sequence from the cDNA clones was most similar to sequences of trypsin-like proteinases from the spruce budworm, Choristoneura fumiferana, and the tobacco hornworm, Manduca sexta. The encoded protein included amino acid sequence motifs of serine proteinase active sites, conserved cysteine residues, and both zymogen activation and signal peptides. Northern blotting analysis showed no major difference between the two strains in mRNA expression in fourth-instar larvae, indicating that transcription was similar in the strains. Southern blotting analysis revealed that the restriction sites for the trypsinogen genes from the susceptible and resistant strains were different. Based on an enzyme size comparison, the cDNA isolated in this study corresponded to the gene for the smaller of two trypsin-like proteinases, which is found in both the Bt-susceptible and -resistant strains of the Indianmeal moth. The sequences reported in this paper have been deposited in the GenBank database (accession numbers AF064525 for the RC688 strain and AF064526 for HD198). [source]

    Effects of different brush border membrane vesicle isolation protocols on proteomic analysis of Cry1Ac binding proteins from the midgut of Helicoverpa armigera

    INSECT SCIENCE, Issue 6 2008
    Li-Zhen Chen
    Abstract Brush border membrane vesicles (BBMV) isolated from insect midguts have been widely used to study Cry1A binding proteins. Sample preparation is important in two-dimensional electrophoresis (2-DE), so to determine a suitable BBMV preparation method in Helicoverpa armigera for 2-DE, we compared three published BBMV preparation methods mostly used in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). All methods yielded similar types and numbers of binding proteins, but in different quantities. The Abdul-Rauf and Ellar protocol was the best of the three, but had limitations. Sufficient protein quantity is important for research involving limited numbers of insects, such as studies of insect resistance to Bacillus thuringiensis in the field. Consequently, we integrated the three BBMV isolation methods into a single protocol that yielded high quantities of BBMV proteins from H. armigera larval midguts, which proved suitable for 2-DE analysis. [source]

    Bias from Farmer Self-Selection in Genetically Modified Crop Productivity Estimates: Evidence from Indian Data

    Benjamin Crost
    Q12; D81 Abstract In the continuing debate over the impact of genetically modified (GM) crops on farmers of developing countries, it is important to accurately measure magnitudes such as farm-level yield gains from GM crop adoption. Yet most farm-level studies in the literature do not control for farmer self-selection, a potentially important source of bias in such estimates. We use farm-level panel data from Indian cotton farmers to investigate the yield effect of GM insect-resistant cotton. We explicitly take into account the fact that the choice of crop variety is an endogenous variable which might lead to bias from self-selection. A production function is estimated using a fixed-effects model to control for selection bias. Our results show that efficient farmers adopt Bacillus thuringiensis (Bt) cotton at a higher rate than their less efficient peers. This suggests that cross-sectional estimates of the yield effect of Bt cotton, which do not control for self-selection effects, are likely to be biased upwards. However, after controlling for selection bias, we still find that there is a significant positive yield effect from adoption of Bt cotton that more than offsets the additional cost of Bt seed. [source]

    Variability of Endotoxin Expression in Bt Transgenic Cotton

    H. Z. Dong
    Abstract Transgenic cotton expressing Bt (Bacillus thuringiensis) toxins is currently cultivated on a large commercial scale in many countries, but observations have shown that it behaves variably in toxin efficacy against target insects under field conditions. Understanding of the temporal and spatial variation in efficacy and the resulting mechanisms is essential for cotton protection and production. In this review, we summarize current knowledge on variability in Bt cotton efficacy, in particular on the induced variability by environmental stresses. We also discuss the resulting mechanisms and the countermeasures for the inconsistence in efficacy in Bt cotton. It is indicated that insecticidal protein content in Bt cotton is variable with plant age, plant structure or under certain environmental stresses. Variability in Bt cotton efficacy against target insect pests is mainly attributed to the changes in Bt protein content, but physiological changes associated with the production of secondary compounds in plant tissues may also play an important role. Reduction of Bt protein content in late-season cotton could be due to the overexpression of Bt gene at earlier stages, which leads to gene regulation at post-transcription levels and consequently results in gene silencing at a later stage. Methylation of the promotor may be also involved in the declined expression of endotoxin proteins. As a part of total protein, the insecticidal protein in plant tissues changes its level through inhibited synthesis, degradation or translocation to developing plant parts, particularly under environmental stresses, thus being closely correlated to N metabolism. It can be concluded that developing new cotton varieties with more powerful resistance, applying certain plant growth regulators, enhancing intra-plant defensive capability, and maintenance of general health of the transgenic crop are important in realizing the full transgenic potential in Bt cotton. [source]

    Spatial and temporal variability in host use by Helicoverpa zea as measured by analyses of stable carbon isotope ratios and gossypol residues

    Graham Head
    Summary 1.,A high dose/refuge strategy has been adopted in the USA to manage the risk of Bacillus thuringiensis (Bt) resistance in target pests such as the cotton bollworm (CBW), Helicoverpa zea (Boddie) in transgenic Bt cotton Gossypium hirsutum L. Structured refuges, consisting of non-Bt cotton, have been a mandated part of this strategy to produce non-selected insects that are temporally and spatially synchronous with insects from the Bt crop, diluting Bt resistance alleles through mating. However, the bollworm is highly polyphagous and exploits a large number of crop and weedy hosts concurrently with Bt cotton. 2.,A study was carried out in five major US cotton-producing states during 2002 and 2003 using the ratios of 13C to 12C in bollworm moths to estimate the proportions of the population originating from C3 or C4 plants. A separate study measured gossypol residues in moths from four states in 2005 and 2006, enabling the identification of moths whose natal hosts were cotton rather than other C3 hosts. 3.,C4 hosts served as the principal source of bollworm moths from mid-to-late June to early September, depending on the state. Beginning in late August/early September and lasting 1,4 weeks, the majority of moths exhibited isotopic compositions characteristic of C3 hosts. During this period, however, the minimum percentage of moths that developed as larvae on C4 hosts was typically >25%. By mid-September and through October and November, the majority of the bollworm population exhibited C4 isotopic compositions. 4.,Between late June and early August, cotton-derived bollworm moths (moths with gossypol residues) comprised <1% of moths in all states, and remained below this level throughout the season in North Carolina. In other states, cotton-derived moths increased between early August and early September to peak at an average of 19·1% of all moths. 5.,Synthesis and applications.,Data on 13C/12C ratios and gossypol residues in CBW moths were used to assess the importance of structured non-Bt cotton refuges for the management of Bt resistance risk in H. zea. Weekly estimates of bollworm breeding on cotton, C3 plants other than cotton and C4 plants showed that, throughout the season, the majority of bollworm moths caught in pheromone traps adjacent to cotton fields did not develop as larvae on cotton. This result implies that management practices in cotton such as the use of structured cotton refuges will play a relatively minor role , particularly compared with maize Zea mays L. , in managing potential resistance to Bt cotton in populations of the CBW in the US Cotton Belt. [source]

    Response of multiple generations of beet armyworm, Spodoptera exigua (Hübner), feeding on transgenic Bt cotton

    G. Wu
    Abstract Development, reproduction and food utilization of three successive generations of beet armyworm, Spodoptera exigua (Hübner), fed on transgenic and non-transgenic Bt cotton were examined. Significantly longer larval life-span and lower pupal weight were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non-transgenic Bt cotton. Significantly higher survival rate and adult fecundity of S. exigua were found in three successive generations of S. exigua fed on transgenic Bt cotton compared with non-transgenic Bt cotton. The survival rate and adult fecundity of S. exigua were occurred significant increase in the third generation compared with the first generation after feeding on transgenic Bt cotton. Significantly lower consumption, frass and relative growth rate (RGR) were observed in three successive generations of S. exigua fed on transgenic Bt cotton compared with non-transgenic Bt cotton. Cotton variety significantly affected all indices of larval consumption and utilization in three successive generations of S. exigua, except for efficiency of conversion of ingested food. However, beet armyworm generation only significantly affected RGR of S. exigua. The results of this study indicated food quality on the diet-utilization efficiency of S. exigua was different along with beet armyworm generation. Measuring multigenerational development and food utilization of S. exigua at individual and population level in response to Bacillus thuringiensis (Bt) can provide a more meaningful evaluation of long-term population dynamics than experiments on a single generation. It is imperative to develop an appropriate multigenerational pest management tactic to monitor the field population dynamics of non-target pests (e.g., beet armyworm) in agricultural Bt cotton ecosystem. [source]

    Determination of baseline susceptibility to Cry1Ab protein for Asian corn borer (Lep., Crambidae)

    K. He
    Abstract:, Although transgenic Bacillus thuringiensis (Bt) corn can provide a new tool for control of the Asian corn borer (ACB), Ostrinia furnacalis (Guenée), concern has been raised regarding the possibility of the target insect evolving resistance to the Bt protein under intensive selection pressure from Bt corn. Therefore, it is necessary to establish baseline data to enable detection of changes in susceptibility in field populations after prolonged exposure to Bt corn. Susceptibility to purified Cry1Ab protein from Bt was determined for 10 populations of ACB from the major corn-growing regions of China, ranging geographically from Heilongjiang Province in the northeast to Shaanxi Province in the east-central part. Neonate ACB were exposed to semi-artificial diet incorporated with increasing Cry1Ab protein concentrations, and mortality and growth inhibition were evaluated after 7 days. The range of LC50 (50% lethal concentration) among the populations was 0.10 to 0.81 ,g/g (Cry1Ab protein/diet). Differences (P < 0.05) in susceptibility among the populations were significant. LC50s generated from the Huanghuaihai Summer Corn Region were higher than those from the Spring Corn Regions. Bt was one of the significant natural biomortality factors of overwintering generation ACB. There was a significant correlation between percentage of the larvae infected with Bt and their LC50 values to Cry1Ab protein in geographic distinct populations (r = 0.7350*, d.f. = 8, r0.05 = 0.632). Based on the background of Bt formulations used for corn insect pests control in these areas, these differences were not caused by prior exposure to Bt insecticides. Instead, the small differences likely reflect natural Bt selection pressure. Because the variation in susceptibility to Cry1Ab was small (<10-fold), the ACB apparently is susceptible to Cry1Ab across its range within China. [source]

    Control of Plutella xylostella using polymer-formulated Steinernema carpocapsae and Bacillus thuringiensis in cabbage fields

    S. Schroer
    Abstract:, Field trials evaluating the potential of the entomopathogenic nematode Steinernema carpocapsae and the feasibility to combine nematodes with Bacillus thuringiensis for sustainable control of the diamondback moth (DBM) Plutella xylostella were conducted in cabbage cultivated in the province Probolinggo, east Java and Indonesia. A single use of 0.5 million S. carpocapsae m,2 applied with a surfactant-polymer-formulation containing 0.3% xanthan and 0.3% Rimulgan® achieved a significant reduction of the insects per plant with >50% control after 7 days. Even 14 days after the application about 45% control was recorded and dead larvae containing nematodes were found. No significant effects were recorded when the formulation was compared with nematodes applied in water or with a surfactant alone. This was attributed to high humidity in the experimental area at the end of the rainy season and a microclimate in the cabbage heads favouring nematode survival. Weekly applications of B. thuringiensis (Turex®) or alternating applications of Turex® and the nematodes achieved >80% control. The application of both biological agents together every second week reached insignificant lower efficacy (70%). Nematodes can be used to substitute ineffective chemical insecticides and alterations with B. thuringiensis can prevent the further development of resistance against the bacterial control agent. [source]

    Recombinant Bacillus thuringiensis strain shows high insecticidal activity against Plutella xylostella and Leptinotarsa decemlineata without affecting nontarget species in the field

    G. Wang
    Abstract Aims:, To construct a recombinant Bacillus thuringiensis (Bt) strain with broad insecticidal spectrum and investigate its impact on nontarget organisms in field. Method and Results:, The cry -type gene of wild Bt strain UV17 was identified and a novel cry1Ba gene was cloned. The cry3Aa7 gene, which was highly toxic to coleopteran pests, was introduced into UV17, and a recombinant strain designated as UV173A was obtained. Bioassay results showed that UV173A was not only highly toxic against Plutella xylostella (50% lethal concentration [LC50] = 18·03 ,g ml,1), but also against coleopteran Leptinotarsa decernlineata (LC50 = 0·19 mg ml,1). The recombinant strain was then tested in field trials to monitor its spatial variation of population and to investigate the impact on nontarget invertebrates. Conclusions:, A recombinant Bt stain UV173A with broad insecticidal spectrum was obtained, and it did not cause adverse effects on the population of nontarget organisms. Significance and Impact of the Study:, The results obtained here indicated that cry1Ba3 gene may be useful for the resistance management of P. xylostella, and the recombinant stain UV173A was potential for field application against some crucifer vegetable pests as well as L. decemlineata. [source]

    Difference between the spore sizes of Bacillus anthracis and other Bacillus species

    M. Carrera
    Abstract Aims:, To determine the size distribution of the spores of Bacillus anthracis, and compare its size with other Bacillus species grown and sporulated under similar conditions. Methods and Results:, Spores from several Bacillus species, including seven strains of B. anthracis and six close neighbours, were prepared and studied using identical media, protocols and instruments. Here, we report the spore length and diameter distributions, as determined by transmission electron microscopy (TEM). We calculated the aspect ratio and volume of each spore. All the studied strains of B. anthracis had similar diameter (mean range between 0·81 ± 0·08 ,m and 0·86 ± 0·08 ,m). The mean lengths of the spores from different B. anthracis strains fell into two significantly different groups: one with mean spore lengths 1·26 ± 0·13 ,m or shorter, and another group of strains with mean spore lengths between 1·49 and 1·67 ,m. The strains of B. anthracis that were significantly shorter also sporulated with higher yield at relatively lower temperature. The grouping of B. anthracis strains by size and sporulation temperature did not correlate with their respective virulence. Conclusions:, The spores of Bacillus subtilis and Bacillus atrophaeus (previously named Bacillus globigii), two commonly used simulants of B. anthracis, were considerably smaller in length, diameter and volume than all the B. anthracis spores studied. Although rarely used as simulants, the spores of Bacillus cereus and Bacillus thuringiensis had dimensions similar to those of B. anthracis. Significance and Impact of the Study:, Spores of nonvirulent Bacillus species are often used as simulants in the development and testing of countermeasures for biodefence against B. anthracis. The data presented here should help in the selection of simulants that better resemble the properties of B. anthracis, and thus, more accurately represent the performance of collectors, detectors and other countermeasures against this threat agent. [source]

    Virulent spores of Bacillus anthracis and other Bacillus species deposited on solid surfaces have similar sensitivity to chemical decontaminants

    J-L. Sagripanti
    Abstract Aims:, To compare the relative sensitivity of Bacillus anthracis and spores of other Bacillus spp. deposited on different solid surfaces to inactivation by liquid chemical disinfecting agents. Methods and Results:, We prepared under similar conditions spores from five different virulent and three attenuated strains of B. anthracis, as well as spores of Bacillus subtilis, Bacillus atrophaeus (previously known as Bacillus globigii), Bacillus cereus, Bacillus thuringiensis and Bacillus megaterium. As spore-surface interactions may bias inactivation experiments, we evaluated the relative binding of different spores to carrier materials. The survival of spores deposited on glass, metallic or polymeric surfaces were quantitatively measured by ASTM standard method E-2414-05 which recovers spores from surfaces by increasing stringency. The number of spores inactivated by each decontaminant was similar and generally within 1 log among the 12 different Bacillus strains tested. This similarity among Bacillus strains and species was observed through a range of sporicidal efficacy on spores deposited on painted metal, polymeric rubber or glass. Conclusions:, The data obtained indicate that the sensitivity of common simulants (B. atrophaeus and B. subtilis), as well as spores of B. cereus, B. thuringiensis, and B. megaterium, to inactivation by products that contain either: peroxide, chlorine or oxidants is similar to that shown by spores from all eight B. anthracis strains studied. Significance and Impact of the Study:, The comparative results of the present study suggest that decontamination and sterilization data obtained with simulants can be safely extrapolated to virulent spores of B. anthracis. Thus, valid conclusions on sporicidal efficacy could be drawn from safer and less costly experiments employing non-pathogenic spore simulants. [source]

    Beyond the spore , past and future developments of Bacillus thuringiensis as a biopesticide

    N. Crickmore
    Abstract Formulated and sporulated cultures of Bacillus thuringiensis (Bt) are widely used as foliar sprays as part of integrated pest management strategies against insect pests of agricultural crops. Although in several cases the presence of the spore has been shown to improve the activity of the product, other Bt -based insecticides have been developed in which the spore is absent. The most notable of these are transgenic plants expressing just the insect toxin gene from the bacterium. This paper will discuss these developments, and the advantages and disadvantages of having the spore present. [source]

    Expression of vip1/vip2 genes in Escherichia coli and Bacillus thuringiensis and the analysis of their signal peptides

    Y. Shi
    Abstract Aims:, To determine the expression time courses and high expression level of Vip2A(c) and Vip1A(c) in Bacillus thuringiensis, and survey their insecticidal toxicity and insecticidal spectrum. Methods and Results:, A kind of new vegetative insecticidal toxin genes encoded by a single operon from B. thuringiensis had been cloned and sequenced. The individual genes, 5-terminus truncated genes and the operon were respectively expressed in Escherichia coli. Only N-terminus deleted Vip2A(c) and Vip1A(c) proteins could be purified by Ni-NTA agarose, while others were processed and their N-terminal signal peptides were cleaved. The individual genes and the operon were also expressed in B. thuringiensis. Both proteins were mostly secreted into the cell supernatants. The expression level of Vip1A(c) was influenced because of the interruption of vip2A(c) gene on the operon. Bioassays showed that neither separate protein nor both performed any toxicity against tested lepidopteran and coleopteran insects. Conclusions:, Vip2A(c) and Vip1A(c) have similar secretion mechanism in E. coli and B. thuringiensis. Vip1A(c) remained its high expression level only when being expressed with vip2A(c) gene as an operon in B. thuringiensis. Significance and Impact of the Study:, Expression of vip2A(c) and vip1A(c) genes in E. coli and B. thuringiensis were investigated. This would help to make clear the secretion mechanism of VIP proteins and study the function of ADP-ribosyltransferase Vip2. [source]

    Detection and characterization of the novel bacteriocin entomocin 9, and safety evaluation of its producer, Bacillus thuringiensis ssp. entomocidus HD9

    A. Cherif
    Abstract Aims: To identify and characterize new bacteriocins from a collection of 41 strains belonging to 27 subspecies of Bacillus thuringiensis, and to evaluate the safety of the producers. Methods and Results:Bacillus thuringiensis ssp. entomocidus HD9 produced in the culture supernatant an antimicrobial activity against Gram-positive bacteria including Listeria monocytogenes, one of four pathogenic Pseudomonas aeruginosa and several fungi. Production of the antibacterial activity, named entomocin 9, started during mid-logarithmic growth reaching its maximum at the early stationary phase. Entomocin 9 retained more than 72% of activity after incubation for 20 min at 121°C. Activity was lost after proteinase K treatment, it was stable in a pH range between 3 and 9, and resistant to lyophilization. After partial purification with ammonium sulphate precipitation followed by gel-filtration and anion-exchange chromatography, an active protein of ca 12·4 kDa was isolated. The mode of action of entomocin 9 was bactericidal and caused cell lysis of growing cells. Despite the presence of a range of virulence related genes, including haemolysin BL, nonhaemolytic enterotoxin, cytotoxin K and several hydrolytic activities, B. thuringiensis HD9 was not toxic against Vero cells. Conclusions: Entomocin 9 is a novel heat-stable, bacteriocin produced by B. thuringiensis HD9. The absence of toxicity against Vero cells suggests the suitability of strain HD9 for a safe application in antimicrobial treatments. Significance and Impact of the Study: New finding on entomocin 9 would make B. thuringiensis attractive in biotechnological applications as an antimicrobial agent in agriculture and food industry. [source]

    Chitinolytic activities in Bacillus thuringiensis and their synergistic effects on larvicidal activity

    M. Liu
    Aims: To investigate the distribution of chitinase in Bacillus thuringiensis strains, and the enhancing effects of the chitinase-producing B. thuringiensis strains on insecticidal toxicity of active B. thuringiensis strain against Spodoptera exigua larvae. Methods and Results: The chitinolytic activities of B.thuringiensis strains representing the 70 serotypes were investigated by the whitish opaque halo and the colorimetric method. Thirty-eight strains produced different levels of chitinase at pH 7·0, and so did 17 strains at pH 10·0. The strain T04A001 exhibited the highest production, reaching a specific activity of 355 U ml,1 in liquid medium. SDS-PAGE and Western blotting showed that the chitinase produced by some B. thuringiensis strains had a molecular weight of about 61 kDa. The bioassay results indicated that the chitinase-producing B. thuringiensis strains could enhance the insecticidal activity of B. thuringiensis strain DL5789 against S. exigua larvae, with an enhancing ratio of 2·35-fold. Conclusion: This study demonstrated that chitinase was widely produced in B. thuringiensis strains and some of the strains could enhance the toxicity of active B. thuringiensis strain. Significance and Impact of the Study: This is the first investigation devoted exclusively to analyse the distribution of chitinase in B. thuringiensis. It infers that the chitinase produced by B. thuringiensis might play a role in the activity of the biopesticide. [source]

    Delaying evolution of insect resistance to transgenic crops by decreasing dominance and heritability

    B. E. Tabashnik
    Abstract The refuge strategy is used widely for delaying evolution of insect resistance to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. Farmers grow refuges of host plants that do not produce Bt toxins to promote survival of susceptible pests. Many modelling studies predict that refuges will delay resistance longest if alleles conferring resistance are rare, most resistant adults mate with susceptible adults, and Bt plants have sufficiently high toxin concentration to kill heterozygous progeny from such matings. In contrast, based on their model of the cotton pest Heliothis virescens, Vacher et al. (Journal of Evolutionary Biology, 16, 2003, 378) concluded that low rather than high toxin doses would delay resistance most effectively. We demonstrate here that their conclusion arises from invalid assumptions about larval concentration-mortality responses and dominance of resistance. Incorporation of bioassay data from H. virescens and another key cotton pest (Pectinophora gossypiella) into a population genetic model shows that toxin concentrations high enough to kill all or nearly all heterozygotes should delay resistance longer than lower concentrations. [source]