Bitrophic and tritrophic effects of <Emphasis Type="Italic">Bt</Emphasis> Cry3A transgenic potato on beneficial,non-target,beetles

Insect-resistant transgenic plants have been suggested to have unpredictable effects on the biodiversity of the agro-ecosystem, including potential effects on insect natural enemies, beneficial in control of crop pests. Whilst carnivorous as adults, many of these predators may also consume plant tissues, in particular plant pollen and nectar. Coleoptera are important in terms of agro-ecological research not only because of the large number of species in this order, but also because of their role as biological control agents. Thus any detrimental impact on this group of insects would be highly undesirable. The effects of potato expressing the coleopteran-specific Bacillus thuringiensis δ-endotoxin Cry3A (Bt Cry3A) on the ladybird beetle Harmonia axyridis and the carabid beetle Nebria brevicollis were investigated via the bitrophic interaction of the adult ladybird with potato flowers and the tritrophic interaction of the carabid consuming a non-target potato pest. Immunoassays confirmed accumulation of the transgene product in potato leaves and floral tissues (at levels of up to 0.01% (pollen) and 0.0285% (anthers) of total soluble protein). Despite H. axyridis and N. brevicollis belonging to the targeted insect order, no significant effects upon survival or overall body mass change of either beetle were observed. Furthermore, Bt Cry3A had no detrimental effects on reproductive fitness of either beetle species, either in terms of fecundity or subsequent egg viability. Behavioural analysis revealed no significant impact of Bt Cry3A on beetle activity or locomoter behaviour. Ligand blots indicate that this is due to either the absence of Bt-binding sites in brush border membrane vesicles (BBMV) isolated from Nebria brevicollis, or in the case of Harmonia axyridis, the binding did not functionally lead to behavioural or physical effects.     

Prey-mediated effects of transgenic canola on a beneficial, non-target, carabid beetle

Transgenic plants producing insecticidal proteins from Bacillus thuringiensis (Bt) can control some major insect pests and reduce reliance on sprayed insecticides. However, large scale adoption of this technology has raised concerns about potential negative effects, including evolution of pest resistance to Bt toxins, transgene flow from Bt crops to other plants, and harm to non-target beneficial organisms. Furthermore, concern has also been expressed over the effects this technology may have on biodiversity in general. Ecologically relevant risk assessment is therefore required (Risk = Hazard × Exposure). Transgenic plants that produce Bt toxins to kill insect pests could harm beneficial predators. This might occur directly by transmission of toxin via prey, or indirectly by toxin-induced reduction in prey quality (Hazard). To test these hypotheses, we determined the effects of Bt-producing canola on a predatory ground beetle (Pterostichus madidus) fed larvae of diamondback moth (Plutella xylostella) that were either susceptible or resistant to the Bt toxin. Survival, weight gain, and adult reproductive fitness did not differ between beetles fed prey reared on Bt-producing plants and those fed prey from control plants. Furthermore, while Bt-resistant prey was shown to deliver high levels of toxin to the beetle when they were consumed, no significant impact upon the beetle was observed. Subsequent investigation showed that in choice tests (Exposure), starved and partially satiated female beetles avoided Bt-fed susceptible prey, but not Bt-fed resistant prey. However, in the rare cases when starved females initially selected Bt-fed susceptible prey, they rapidly rejected them after beginning to feed. This prey type was shown to provide sufficient nutrition to support reproduction in the bioassay suggesting that Bt-fed susceptible prey is acceptable in the absence of alternative prey, however adults possess a discrimination ability based on prey quality. These results suggest that the direct effects of Bt-producing canola on predator life history was minimal, and that predators’ behavioural preferences may mitigate negative indirect effects of reduced quality of prey caused by consumption of Bt-producing plants. The results presented here therefore suggest that cultivation of Bt canola may lead to conservation of non-target predatory and scavenging organisms beneficial in pest control, such as carabids, and may therefore provide more sustainable agricultural systems than current practices. In addition, minimal impacts on beneficial carabids in agro-ecosystems suggest that Bt canola crops are likely to be compatible with integrated pest management (IPM) systems.     

The effects of pollen consumption of transgenic Bt maize on the common swallowtail, Papilio machaon L. (Lepidoptera, Papilionidae)

Effects of exposure to maize pollen of event Bt176 (cultivar “Navares”) on the larvae of the European common swallowtail (Papilio machaon L.) were studied in the laboratory. First instar larvae were exposed to different pollen densities applied to leaf disks of Pastinaca sativa L. for 48 h. Pollen densities applied in this study were in the range recorded from the field. Larvae which were exposed to higher Bt maize pollen densities consumed more pollen and had a lower survival rate. The LD₅₀ with regard to larvae surviving to adulthood was 13.72 pollen grains consumed by first-instar larva. Uptake of Bt maize pollen led to a reduced plant consumption, to a lower body weight, and to a longer development time of larvae. Effects on pupal weight and duration of the pupal period were present but less pronounced and smaller than effects on larvae. Larvae having consumed Bt-maize pollen as first instars had a lower body weight as adult females and smaller forewings as adult males. We conclude that possible effects of Bt maize on European butterflies and moths must be evaluated more rigorously before Bt maize should be cultivated over large areas.     

Altered host plant preference of Tetranychus urticae and prey preference of its predator Phytoseiulus persimilis (Acari: Tetranychidae, Phytoseiidae) on transgenic Cry3Bb-eggplants

The behavior of the two-spotted spider mite, Tetranychus urticae Koch and the predatory mite Phytoseiulus persimilis A.-H. was investigated in laboratory experiments with transgenic Bt-eggplants, Solanum melongena L., producing the Cry3Bb toxin and corresponding isogenic, non-transformed eggplants. In bitrophic experiments, dual-choice disc tests were conducted to reveal the effects of transgenic eggplants on host plant preference of T. urticae. Adult spider mite females were individually placed on leaf discs (2 cm diameter) and were observed during five days. Females occurred significantly more frequently on transgenic halves on which also significantly more T. urticae eggs were found. The effects of a Cry3Bb-eggplant fed prey on the feeding preference of P. persimilis were investigated in tritrophic experiments. Sixteen spider mite females, eight of which had been taken from transgenic and eight from isogenic eggplants, were offered to well-fed females of P. persimilis and numbers of respective spider mites consumed were registered 12 h later when the predators were offered new spider mites again. This procedure was repeated six times. The results revealed that predatory mites consumed significantly less Bt-fed spider mites than prey that had been raised on control eggplants. These results indicate that eggplants expressing the Cry3Bb toxin for resistance against the Colorado potato beetle are more preferred by spider mites but are less preferred by their predator P. persimilis. Possible consequences of these findings for biological control of spider mites on eggplants are discussed.     

Field trials to evaluate effects of Bt-transgenic silage corn expressing the Cry1Ab insecticidal toxin on non-target soil arthropods in northern New England, USA

Traditionally, control of European corn borer (Ostrinia nubilalis) Hübner has been achieved through the use of chemical insecticides. With increasing emphasis on reducing pesticide inputs in agricultural production, alternative management technologies are now being used including transgenic silage corn modified to express Cry1Ab protein toxins derived from Bacillus thuringiensis (Bt) Berliner. The Cry1Ab toxin is expressed by all plant cells and throughout the growing season. Furthermore, the toxins are exuded from corn plant roots into the rhizosphere, raising concerns over possible side-effects on non-target beneficial organisms in the same habitat. In addition, detrivores are exposed to crop residues containing the toxin when incorporated into the soil. The current 2-year study (2003, 2004) evaluated effects of two silage-corn varieties: Pioneer var. 38A25 (Bt-corn expressing the Cry1Ab toxin) and Pioneer var. 38A24 (parent isoline) on species diversity and evenness of carabid beetles and Collembola. Pitfall traps were used to collect surface-dwelling species on a bimonthly schedule from April to October. Soil cores were taken once a month from April to October to sample subterranean species, which were extracted using Berlese funnels. All individuals were recorded and identified where possible to species level for analysis in the Simpson’s D and Shannon–Wiener H’ diversity indices. Evenness was measured using Simpson’s E’, after which dominant species were analyzed in a multivariate ordination analysis. Results showed Bt-corn had no negative effects on any of the organisms analyzed. There was a significant year effect on the abundance of surface-dwelling Collembola and on species diversity of soil-dwelling Collembola. Our findings suggest that crop management practices and/or environmental conditions (e.g., heavy rainfall during the 2004 growing season) had the greatest impact on species diversity and evenness, rather than the crop itself (Bt or isoline).     

Host-plant mediated effects of transgenic maize on the insect parasitoid Campoletis sonorensis (Hymenoptera: Ichneumonidae)

Determining the impact of genetically modified (GM) crops on beneficial organisms is an important aspect of the environmental risk assessment of GM crops. In the present study, the impact of Bt maize expressing Cry1Ab on the development and behaviour of the parasitoid Campoletis sonorensis was compared to individuals reared on hosts fed conventionally bred plants partially resistant to the European corn borer (Ostrinia nubilalis Hübner) and on susceptible maize hybrids. Adult parasitoids reared on Bt maize-fed Spodoptera frugiperda larvae were significantly smaller (15–30%) than those reared in hosts fed either of the conventional maize hybrids. The magnitude of this effect was dependent on the size of the host at oviposition and its subsequent growth rate. The development time of C. sonorensis was not affected by the maize treatment. In choice tests, female parasitoids displayed no preference for hosts fed a specific maize hybrid. No Cry1Ab was detected within adult parasitoids.     

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

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.     

Non-target impacts of forest defoliator management options: Decision for no spraying may have worse impacts on non-target Lepidoptera than Bacillus thuringiensis insecticides

Management programs for major forest defoliators such as gypsy moths or forest tent caterpillars, and crop pests such as the European corn borer have shifted from broad-spectrum insecticides to more environmentally benign microbial pesticides such as Bacillus thuringiensis (foliage sprays and transgenic toxin expression in plant tissues). Phytochemically resistant host plants and natural enemies have been used as alternative pest management strategies (including generalist tachinid flies such as Compsilura, viruses, microsporidians, and fungi), but all of these have some non-target impacts, as described from literature review. A sequence of lab and field studies were conducted to determine non-target impacts on native Lepidoptera in North America. The conclusions reached are that a decision not to spray Bt pesticides (i.e. to allow defoliation and natural pest outbreaks to run their course) could be as bad or worse for non-target Lepidoptera as the microbial insecticides would be. The important concept that must be maintained is that all pest management programs have some risk of negative non-target impacts, but it is the magnitude and relative importance that will remain the most critical issue for environmental impacts and pest management.     

Implications of transgenic, insecticidal plants for insect and plant biodiversity

Genetically modified plants are widely grown predominantly in North America and to a lesser extent in Australia, Argentina and China but their regions of production are expected to spread soon beyond these limited areas also reaching Europe where great controversy over the application of gene technology in agriculture persists. Currently, several cultivars of eight major crop plants are commercially available including canola, corn, cotton, potato, soybean, sugar beet, tobacco and tomato, but many more plants with new and combined multiple traits are close to registration. While currently agronomic traits (herbicide resistance, insect resistance) dominate, traits conferring “quality” traits (altered oil compositions, protein and starch contents) will begin to dominate within the next years. However, economically the most promising future lies in the development and marketing of crop plants expressing pharmaceutical or “nutraceuticals” (functional foods), and plants that express a number of different genes. From this it is clear that future agricultural and, ultimately, also natural ecosystems will be challenged by the large-scale introduction of entirely novel genes and gene products in new combinations at high frequencies all of which will have unknown impacts on their associated complex of non-target organisms, i.e. all organisms that are not targeted by the insecticidal protein. In times of severe global decline of biodiversity, pro-active precaution is necessary and careful consideration of the likely expected effects of transgenic plants on biodiversity of plants and insects is mandatory.In this paper possible implications of non-target effects for insect and plant biodiversity are discussed and a case example of such non-target effects is presented. In a multiple year research project, tritrophic and bitrophic effects of transgenic corn, expressing the gene from Bacillus thuringiensis (Bt-corn) that codes for the high expression of an insecticidal toxin (Cry1Ab), on the natural enemy species, Chrysoperla carnea (the green lacewing), was investigated. In these laboratory trials, we found prey-mediated effects of transgenic Bt-corn causing significantly higher mortality of C. carnea larvae. In further laboratory trials, we confirmed that the route of exposure (fed directly or via a herbivorous prey) and the origin of the Bt (from transgenic plants or incorporated into artificial diet) strongly influenced the degree of mortality. In choice feeding trials where C. carnea could choose between Spodoptera littoralis fed transgenic Bt-corn and S. littoralis fed non-transgenic corn, larger instars showed a significant preference for S. littoralis fed non-transgenic corn while this was not the case when the choice was between Bt- and isogenic corn fed aphids. Field implications of these findings could be multifold but will be difficult to assess because they interfere in very intricate ways with complex ecosystem processes that we still know only very little about. The future challenge in pest management will be to explore how transgenic plants can be incorporated as safe and effective components of IPM systems and what gene technology can contribute to the needs of a modern sustainable agriculture that avoids or reduces adverse impacts on biodiversity? For mainly economically motivated resistance management purposes, constitutive high expression of Bt-toxins in transgenic plants is promoted seeking to kill almost 100% of all susceptible (and if possible heterozygote resistant) target pest insects. However, for pest management this is usually not necessary. Control at or below an established economic injury level is sufficient for most pests and cropping systems. It is proposed that partially or moderately resistant plants expressing quantitative rather than single gene traits and affecting the target pest sub-lethally may provide a more meaningful contribution of agricultural biotechnology to modern sustainable agriculture. Some examples of such plants produced through conventional breeding are presented. Non-target effects may be less severe allowing for better incorporation of these plants into IPM or biological control programs using multiple control strategies, thereby, also reducing selection pressure for pest resistance development.     

Risk assessment and ecological effects of transgenic Bacillus thuringiensis crops on non-target organisms

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.     

A 3-year field-scale monitoring of foliage-dwelling spiders (Araneae) in transgenic Bt maize fields and adjacent field margins

Concerns have been raised that genetically modified Bt maize may harm non-target organisms, and there is a general call and need for a risk assessment of Bt maize. Spiders are important pest predators in agroecosystems and in maize, and can be exposed to the Bt toxin by herbivorous or pollen-collecting prey, by active Bt maize pollen feeding, and by ingesting their pollen-dusted webs. The foliage-dwelling spider fauna of Bt maize fields and adjacent margins was monitored and compared to non-transgenic maize fields. The study took place during the vegetation seasons of 2001–2003 in Bavaria, South Germany. Maize fields and adjacent nettle field margins were colonized by a typical spider assemblage, dominated by space-web spiders (Theridiidae and Linyphiidae). Abundance and species richness of spiders was higher in nettle margins than in maize fields. The proportion of hunting spiders tended to be higher in nettle margins, whereas space-web spiders tended to be more frequent in maize fields. Bt maize showed no consistent effect on individual numbers, species richness and guild structure of spiders in maize fields and adjacent nettle field margin strips. The spider abundance was higher in Bt treatments in 2003, whereas in 2001 and 2002 no significant differences were found. The results provide an important contribution for the implementation of case-specific and general surveillance of transgenic plants to be employed due to the regulations of the European Community.     

Open field host selection and behavior by tamarisk beetles (Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars (Tamarix spp.) and risks to non-target athel (T. aphylla) and native Frankenia spp.

Biological control of invasive saltcedars (Tamarix spp.) in the western U.S. by exotic tamarisk leaf beetles, Diorhabda spp., first released in 2001 after 15 years of development, has been successful. In Texas, beetles from Crete, Greece were first released in 2004 and are providing control. However, adults alight, feed and oviposit on athel (Tamarix aphylla), an evergreen tree used for shade and as a windbreak in the southwestern U.S. and México, and occasionally feed on native Frankenia spp. plants. The ability of tamarisk beetles to establish on these potential field hosts was investigated in the field. In no-choice tests in bagged branches, beetle species from Crete and Sfax, Tunisia produced 30–45% as many egg masses and 40–60% as many larvae on athel as on saltcedar. In uncaged choice tests in south Texas, adult, egg mass and larval densities were 10-fold higher on saltcedar than on adjacent athel trees after 2 weeks, and damage by the beetles was 2- to 10-fold greater on saltcedar. At a site near Big Spring, in west-central Texas, adults, egg masses and 1st and 2nd instar larvae were 2- to 8-fold more abundant on saltcedar than on athel planted within a mature saltcedar stand being defoliated by Crete beetles, and beetles were 200-fold or less abundant or not found at all on Frankenia. At a site near Lovelock, Nevada, damage by beetles of a species collected from Fukang, China was 12–78% higher on saltcedar than on athel planted among mature saltcedar trees undergoing defoliation. The results demonstrate that 50–90% reduced oviposition on athel and beetle dispersal patterns within resident saltcedar limit the ability of Diorhabda spp. to establish populations and have impact on athel in the field.     

The emergence of transgenic potatoes as commercial products and tools for basic science

The potato has tremendous potential as a transgenic crop and is a good model system by which to analyse metabolic regulation and gene expression. The potato’s difficult genetics, but ease of genetic transformation and its clonal means of propagation make it ideal for applied agricultural molecular genetics. Thus, the next 4 years promise to put the potato (with a diversity of transgenic constructs expressed) in the limelight as many of the first transgenic agricultural products enter the marketplace.     

Transgenic Bt potato and conventional insecticides for Colorado potato beetle management: comparative efficacy and non-target impacts

Field studies were conducted in 1992 and 1993 in Hermiston, Oregon, to evaluate the efficacy of transgenic Bt potato (Newleaf^®, which expresses the insecticidal protein Cry3Aa) and conventional insecticide spray programs against the important potato pest, Leptinotarsa decemlineata (Say), Colorado potato beetle (CPB), and their relative impact on non-target arthropods in potato ecosystems. Results from the two years of field trials demonstrated that Newleaf potato plants were highly effective in suppressing populations of CPB, and provided better CPB control than weekly sprays of a microbial Bt-based formulation containing Cry3Aa, bi-weekly applications of permethrin, or early- and mid-season applications of systemic insecticides (phorate and disulfoton). When compared with conventional potato plants not treated with any insecticides, the effective control of CPB by Newleaf potato plants or weekly sprays of a Bt-based formulation did not significantly impact the abundance of beneficial predators or secondary potato pests. In contrast to Newleaf potato plants or microbial Bt formulations, however, bi-weekly applications of permethrin significantly reduced the abundance of several major generalist predators such as spiders (Araneae), big-eyed bugs (Geocorus sp.), damsel bugs (Nabid sp.), and minute pirate bugs (Orius sp.), and resulted in significant increases in the abundance of green peach aphid (GPA), Myzus persicae (Sulzer) – vector of viral diseases, on the treated potato plots. While systemic insecticides appeared to have reduced the abundance of some plant sap-feeding insects such as GPA, lygus bugs, and leafhoppers, early and mid-season applications of these insecticides had no significant impact on populations of the major beneficial predators. Thus, transgenic Bt potato, Bt-based microbial formulations and systemic insecticides appeared to be compatible with the development of integrated pest management (IPM) against other potato pests such as GPA because these CPB control measures have little impact on major natural enemies. In contrast, the broad-spectrum pyrethroid insecticide (permethrin) is less compatible with IPM programs against GPA and the potato leafroll viral disease.     

Assessment of ecological risks in weed biocontrol: Input from retrospective ecological analyses

Prediction of the outcomes of natural enemy introductions remains the most fundamental challenge in biological control. Quantitative retrospective analyses of ongoing biocontrol projects provide a systematic strategy to evaluate and further develop ecological risk assessment. In this review, we highlight a crucial assumption underlying a continued reliance on the host specificity paradigm as a quantitative prediction of ecological risk, summarize the status of our retrospective analyses of nontarget effects of two weevils used against exotic thistles in North America, and discuss our prospective assessment of risk to a federally listed, threatened species (Cirsium pitcheri) based on those studies. Our analyses quantify the fact that host range and preference from host specificity tests are not sufficient to predict ecological impact if the introduced natural enemy is not strictly monophagous. The implicit assumption when such use is made of the host specificity data in risk assessment is that population impacts are proportional to relative preference and performance, the key components of host specificity. However, in concert with shifting awareness in the field, our studies demonstrate that the environment influences and can alter host use and population growth, leading to higher than expected direct impacts on the less preferred native host species at several spatial scales. Further, we have found that straightforward, easily anticipated indirect effects, on intraguild foragers as well as on the less preferred native host plant species, can be both widespread and significant. We conclude that intensive retrospective ecological studies provide some guidance for the quantitative prospective studies needed to assess candidate biological control agent dynamics and impacts and, so, contribute to improved rigor in the evaluation of total ecological risk to native species.     

Larvicidal activities against agricultural pests of transgenic Escherichia coli expressing combinations of four genes from Bacillus thuringiensis

The genes cry1Ac and cry1Ca from Bacillus thuringiensis subsps. kurstaki HD-73 and aizawai 4J4, respectively, encoding δ-endotoxins against lepidopteran larvae were isolated, cloned and expressed in Escherichia coli, with and without cyt1Aa (encoding cytolytic protein) and p20 (accessory protein) from subsp. israelensis. Nine combinations of the genes under control of an early T7, P _A1 inducible promoter, produced the encoding proteins. Toxicities were examined against larvae of three major agricultural pests: Pectinophora gossypiella, Helicoverpa armigera and Spodoptera littoralis. The clones expressing cyt1Aa, with or without p20, were not toxic. The clone expressing cry1Ac (pBt-1A) was the most toxic to P. gossypiella (LC₅₀ of 0.27 × 10⁸ cells g⁻¹). Clone pBt-1CA expressing cry1Ca and cry1Ac displayed the highest toxicity (LC₅₀ of 0.12 × 10⁸ cells ml⁻¹) against S. littoralis. Clone pBt-1CARCy expressing all four genes (cry1Ca, cry1Ac, p20, cyt1Aa) in tandem exhibited the highest toxicity to H. armigera (LC₅₀ of 0.16 × 10⁸ cells ml⁻¹). Cyt1Aa failed to raise the toxicity of these Cry toxins against P. gossypiella and S. littoralis but significantly enhanced toxicity against H. armigera. Two additional clones expressing either cry1Ac or cry1Ca under tandem promoters, P _A1 and P _psbA (constitutive), displayed significantly higher toxicities (7.5- to 140-fold) than their counterparts with P _A1 alone, reducing the LC₅₀ values to below 10⁷ cells ml⁻¹. Vadim Khasdan and Maria Sapojnik are contributed equally to this work.     

Survival and fecundity of Bt-susceptible Colorado potato beetle adults after consumption of transgenic potato containing Bacillus thuringiensis subsp. tenebrionis Cry3A toxin

Survival and fecundity of Colorado potato beetle adults, Leptinotarsa decemlineata (Say), that had or had not fed previously on non-transgenic potato before exposure to transgenic potato containing the Bacillus thuringiensis subsp. tenebrionis Cry3A toxin (Bt) was investigated. In the laboratory, < 5% of first-generation adults survived after two weeks when restricted to Bt foliage since eclosion, but over 85% of adults that had fed initially on non-Bt potato survived exposure to Bt potato for two weeks. In field experiments, less than 0.5% of adults that were exclusively provided Bt potato plants survived overwinter, whereas 44% to 57% survived overwinter when fed non-Bt potato plants for two weeks before being provided Bt potato as a final pre-overwintering host. Survival through the winter increased as the duration of initial feeding on non-Bt potato increased and was similar for beetles provided either tubers or Bt potato plants as a final pre-overwintering host. Only overwintered beetles that fed initially on non-Bt potato before encountering either tubers or Bt potato as a final pre-overwintering host laid eggs the following spring. Survival and reproduction of potato beetle adults after colonizing Bt potato fields should not be adversely affected as long as they have had sufficient time to feed initially on non-Bt potato. Implications for how potato production practices in the Mid-Atlantic US may affect the utility of general resistance management plans for Bt potato are discussed.     

Complete sequence of three plasmids from Bacillus thuringiensis INTA-FR7-4 environmental isolate and comparison with related plasmids from the Bacillus cereus group

Bacillus thuringiensis is an insect pathogen used worldwide as a bioinsecticide. It belongs to the Bacillus cereus sensu lato group as well as Bacillus anthracis and B. cereus. Plasmids from this group of organisms have been implicated in pathogenicity as they carry the genes responsible for different types of diseases that affect mammals and insects. Some plasmids, like pAW63 and pBT9727, encode a functional conjugation machinery allowing them to be transferred to a recipient cell. They also share extensive homology with the non-functional conjugation apparatus of pXO2 from B. anthracis. In this study we report the complete sequence of three plasmids from an environmental B. thuringiensis isolate from Argentina, obtained by a shotgun sequencing method. We obtained the complete nucleotide sequence of plasmids pFR12 (12 095 bp), pFR12.5 (12 459 bp) and pFR55 (55 712 bp) from B. thuringiensis INTA-FR7-4. pFR12 and pFR12.5 were classified as cryptic as they do not code for any obvious functions besides replication and mobilization. Both small plasmids were classified as RCR plasmids due to similarities with the replicases they encode. Plasmid pFR55 showed a structural organization similar to that observed for plasmids pAW63, pBT9727 and pXO2. pFR55 also shares a tra region with these plasmids, containing genes related to T4SS and conjugation. A comparison between pFR55 and conjugative plasmids led to the postulation that pFR55 is a conjugative plasmid. Genes related to replication functions in pFR55 are different to those described for plasmids with known complete sequences. pFR55 is the first completely sequenced plasmid with a replication machinery related to that of ori44. The analysis of the complete sequence of plasmids from an environmental isolate of B. thuringiensis permitted the identification of a near complete conjugation apparatus in pFR55, resembling those of plasmids pAW63, pBT9727 and pXO2. The availability of this sequence is a step forward in the study of the molecular basis of the conjugative process in Gram positive bacteria, particularly due to the similarity with known conjugation systems. It is also a contribution to the expansion of the non-pathogenic B. cereus plasmid gene pool.     

Developmental polymorphism: a major factor for understanding sublethal effects of Bacillus thuringiensis

Developmental polymorphism in Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) was induced by Bacillus thuringiensis (Berliner) in the laboratory. The B.t. formulation concentration induced a quadratic response on the incidence of developmental polymorphism. A double application of Bacillus thuringiensis at fourth and fifth instar respectively resulted in a higher occurrence of developmental polymorphism than a single application at fifth instar. Smaller larval weight prior to B.t. exposure resulted in higher incidence of developmental polymorphism. However, larvae exhibiting developmental polymorphism exhibited larger pupae and an extended larval period. Thus, developmental polymorphism and Bacillus thuringiensis ingestion together prolonged the development time but induced opposite effects on pupal weight. These findings suggest that the calculation of sublethal effects on pupal weight and development time that include developmental polymorphism as an uncontrolled source of variation could lead to an inadequate understanding of insect response in any stress-induced experiments.     

Generation and characterization of transgenic poplar plants overexpressing a cotton laccase gene

Laccases are copper-containing glycoproteins, which are widespread in higher plants as multigene families. To gain more insight in the function of laccases in plants, especially potential role in lignification, we produced transgenic poplar plants overexpressing a cotton laccase cDNA (GaLAC1) under the control of the cauliflower mosaic virus 35S promoter. As compared with untransformed control plants, transgenic plants exhibited a 2.1- to 13.2-fold increased laccase activity, whereas plant growth rate and morphological characters remained similar to control plants. A 2.1–19.6% increase in total lignin content of the stem was found in transgenic plants. Moreover, transgenic plants showed a dramatically accelerated oxidation rate of phenolics, without obvious change in total phenolic content. Our data suggested that GaLAC1 may participate in lignin synthesis and phenolic metabolism in plants. The present work provided a new genetic evidence for the involvement of plant laccases in lignification.