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1.
Field corn, Zea mays L., plants expressing Cry1Ab and Cry1F insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on considerable acreage across the Southern region of the United States. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an economically important pest during the mid-to-late season on non-Bt and some commercial Bt corn hybrids. The objective of this study was to quantify foliar injury and survivorship of fall armyworm on transgenic corn lines expressing Cry1Ab or Cry1F Bt proteins. Corn lines/hybrids expressing Cry1Ab, Cry1F, and a conventional non-Bt cultivar were evaluated against artificial infestations of fall armyworm in field trials. Larvae (second instars) of fall armyworm were placed on corn plants (V8-V10 stages). Leaf injury ratings were recorded 14 d after infestation. Hybrids expressing Cry1F had significantly lower feeding injury ratings than non-Bt corn plants. Development and survivorship of fall armyworm on Bt corn lines/hybrids were also evaluated in no-choice laboratory assays by offering freshly harvested corn leaf tissue to third instars. Transgenic corn hybrids expressing Cry1Ab or Cry1F significantly reduced growth, development, and survivorship of fall armyworm compared to those offered non-Bt corn tissue. However, 25-76% of third instars offered Bt corn leaf tissues successfully pupated and emerged as adults. These results suggest 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. Although fall armyworm is not considered a primary target for insect resistance management by the U.S. Environmental Protection Agency, these levels of survivorship could impact selection pressures across the farmscape, especially when considering that transgenic Bt cotton cultivars express similar Cry (Cry1Ac or Cry1F) proteins.  相似文献   

2.
Larval survival and oviposition behavior of three genotypes of diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), (homozygous Cry1Ac-susceptibile, Cry1Ac-resistant, and their F1 hybrids), on transgenic Bacillus thuringiensis (Bt) broccoli expressing different levels of Cry1Ac protein were evaluated in laboratory. These Bt broccoli lines were designated as relative low, medium, and high, respectively, according to the Cry1Ac content. Untransformed brocccoli plants were used as control. Larval survival of diamondback moth on non-Bt leaves was not significantly different among the three genotypes. The Cry1Ac-resistant larvae could survive on the low level of Bt broccoli plants, while Cry1Ac-susceptible and F1 larvae could not survive on them. The three genotypes of P. xylostella larvae could not survive on medium and high levels of Bt broccoli. In oviposition choice tests, there was no significant difference in the number of eggs laid by the three P. xylostella genotypes among different Bt broccoli plants. The development of Cry1Ac-susceptible and Cry1Ac-resistant P. xylostella on intact Bt plants was also tested in greenhouse. All susceptible P. xylostella larvae died on all Bt plants, while resistant larvae could survive on broccoli, which expresses low Cry1Ac protein under greenhouse conditions. The results of the greenhouse trials were similar to that of laboratory tests. This study indicated that high dose of Bt toxins in broccoli cultivars or germplasm lines is required for effective resistance management.  相似文献   

3.
Transgenic corn hybrids that express toxins from Bacillus thuringiensis (Bt) are highly effective against the European corn borer, Ostrinia nubilalis (Hübner), and the closely related Asian corn borer, Ostrinia furnacalis (Guenée). Since the registration of Bt corn hybrids in the U.S. in 1996, there has been a great deal of information generated on O. nubilalis. However, relatively little information exists for O. furnacalis. To help determine whether the information generated for O. nubilalis can be leveraged for decisions regarding the use of transgenic Bt corn against O. furnacalis, experiments were designed to determine whether the pattern of sensitivity to various Bt Cry1 toxins is similar between the two species. Test insects included laboratory-reared O. furnacalis originating from Malaysia, a Bt-susceptible laboratory colony of O. nubilalis maintained at the University of Nebraska-Lincoln (UNL) and an out-group consisting of the sugarcane borer, Diatraea saccharalis (F.), from Louisiana which represents a different genus from the same family. O. furnacalis and O. nubilalis exhibited a similar pattern of susceptibility to all the Cry1 toxins and were highly susceptible to the range of Bt toxins tested including Cry1Aa, Cry1Ab, Cry1Ac and Cry1F. Both of the Ostrinia species were more tolerant to Cry1Ba compared with D. saccharalis, although sensitivity of O. furnacalis was intermediate and did not differ significantly from that of O. nubilalis and D. saccharalis. D. saccharalis was also susceptible to the range of toxins tested but unlike the two Ostrinia species, was more tolerant to Cry1F and more susceptible to Cry1Ba. These results indicate that both of the Ostrinia corn borer species are similar in sensitivity to the Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1F toxins, thus suggesting shared toxin receptors and mechanisms of toxicity for the two species.  相似文献   

4.
Monsanto Company and Dow AgroSciences have used conventional breeding techniques to develop the combined-trait corn (Zea mays L.) product MON 89034 × TC1507 × MON 88017 × DAS-59122-7 (“SmartStax® corn”) that confers insect resistance against key lepidopteran pests and the corn rootworm complex (Diabrotica spp.), as well as herbicide tolerance. This product contains the Cry3Bb1, Cry34Ab1, and Cry35Ab1 proteins for corn rootworm (CRW) control. Replicated field trials were conducted in 2006 and 2007 to test the efficacy of Cry3Bb1, Cry34Ab1/Cry35Ab1, and SmartStax under both natural and controlled infestations. In both years, root damage and adult beetle emergence were significantly less for Bt-containing hybrids than for non-Bt controls. In trials with heavy insect pressure, adult beetle emergence (a measure of larval control) was significantly reduced for SmartStax hybrids compared with hybrids with the individual traits and with non-Bt controls. Similarly, strip-plot testing in 2012 in grower fields with high levels of root injury to non-Bt hybrids showed significantly lower feeding on SmartStax than on the non-Bt control or on either single-trait product. In grower fields where single-trait Cry3Bb1 products incurred heavy CRW damage in 2011, SmartStax provided consistent protection against CRW in 2012. The combination of these insecticidal proteins in a single plant provides better rootworm control than current single-trait Bt corn products and represents an effective approach for corn rootworm resistance management.  相似文献   

5.
The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major target of transgenic corn, Zea mays L., expressing Bacillus thuringiensis (Bt) proteins in both North and South America. A highly Cry1F-resistant strain of S. frugiperda was established from a field collection in Puerto Rico in 2011. In this study, three greenhouse trials were conducted to evaluate larval survival and leaf injury of Cry1F-susceptible, -resistant, and -heterozygous genotypes of S. frugiperda on whole plants of five non-Bt and eight Bt corn hybrids. The Bt corn products included two single-gene Bt corn hybrids containing Herculex®I (Cry1F) and YieldGard® (Cry1Ab) traits and six pyramided Bt corn hybrids representing four traits: Genuity® VT Double Pro™, Genuity®VT Triple Pro™, Genuity® SmartStax™, and Agrisure® Viptera™ 3111. In each trial, neonates of S. frugiperda were placed into the plant whorls at vegetative plant stages (V6–V10). Larvae of the three insect genotypes on non-Bt corn hybrids survived well and caused serious plant injury. Cry1Ab corn was ineffective against all three insect genotypes. On Cry1F corn plants, resistant larvae survived on 72.9% plants after 12–15 d and caused a leaf injury rating (Davis' 1 to 9 scales) of 5.7 after 7 d and 7.6 after 12–15 d. Both the larval survivorship and leaf injury rates of the resistant larvae on Cry1F corn plants were not significantly different from those observed on non-Bt corn hybrids. In contrast, no live larvae and little or no leaf injury were observed on the Cry1F corn plants that were infested with susceptible or heterozygous genotypes, or on the pyramided Bt plants. The results demonstrated that the Cry1F-resistant S. frugiperda was highly resistant to whole plants of Cry1F corn and the resistance was recessive. Hybrids that contained one of the four pyramided Bt traits were effective for managing the Cry1F resistance in S. frugiperda.  相似文献   

6.
Cry1A.105 is a Cry protein expressed in some transgenic Bacillus thuringiensis (Bt) maize products. In this study, performance of five populations of fall armyworm, Spodoptera frugiperda (J.E. Smith), were evaluated on four non-Bt and eight commercial and experimental Bt maize hybrids/lines (hereafter referred as maize products). The five insect populations included one Cry1A.105-susceptible strain, two Cry1A.105-resistant strains, and two F1 heterozygous genotypes. The eight Bt maize hybrids/lines consisted of five single-gene Bt maize products containing Cry1A.105, Cry2Ab2, Cry1F, or Cry1Ab protein, and three pyramided Bt maize products expressing Cry1A.105/Cry2Ab2, Cry1A.105/Cry2Ab2/Cry1F, or Cry1Ab/Vip3A for targeting aboveground lepidopteran maize pests. In the study, neonates of each population were tested on leaf tissues in the laboratory and whole plants in the greenhouse. Cry1A.105 and Cry1F maize killed 92.2–100% susceptible larvae in both test methods, while resistant larvae survived well on these two maize products. Performance of the two F1 populations on Cry1A.105 and Cry1F maize varied between the two test methods. In leaf tissue bioassay, Cry1Ab maize was marginally effective against the susceptible population. In contrast, few live larvae and little leaf injury from any of the five populations were observed on Cry2Ab2 and the three pyramided Bt maize products. The results of this study showed evidence of cross resistance of the Cry1A.105-resistant S. frugiperda to Cry1F and Cry1Ab maize, but not to the Bt maize products containing Cry2Ab2 or Vip3A. Data generated from this study will be useful in developing resistance management strategies for the sustainable use of Bt maize technology.  相似文献   

7.
Transgenically expressed Bacillus thuringiensis insecticidal-protein Cry1Ab was quantified in target tissues of insect feeding of several YieldGard® corn hybrids. The Cry1Ab protein is intended to protect corn plants from two economically important stem borers, Chilo partellus and Sesamia inferens. A total of seven YieldGard hybrids, all with MON810 event, were field-tested in a total of fourteen locations during the dry season (October–March) of 2005/2006 and wet season (May–October) of 2006. S. inferens and C. partellus oviposit on leaves of young corn plants, 15–60 days after emergence (DAE). The neonates initially feed by scraping the leaf lamina before migrating to bore into the stem. Thus high concentrations of Cry1Ab in whorl leaf and stem tissues would ensure effective control of the borers. The mean tissue Cry1Ab concentrations during the oviposition window of the borers (15–60 DAE), ranged from 50.05 to 21.01 ppm in whorl leaf, and between 9.26 and 3.47 ppm in stem tissue during the same period in the dry season of 2005/06. Similarly, Cry1Ab concentrations in whorl leaf and stem between 15 and 60 DAE during the wet season of 2006 ranged between 19.30 to 11.08 and 14.28 to 4.69 ppm, respectively. The baseline-sensitivity data of these insects to Cry1Ab in laboratory assays was determined. The concentrations of Cry1Ab in the target tissues as studied in seven YieldGard hybrids tested suggest effective management of the two borers. This paper also provides a summary of the expression of the Cry1Ab gene in various genetic backgrounds.  相似文献   

8.
The sugarcane borer, Diatraea saccharalis (F.), is a key pest of sugarcane and other grasses, which is a current focus of research aiming to develop transgenically resistant genotypes. However, the current susceptibility of Brazilian populations of the sugarcane borer to Bt toxins is unknown. Laboratory assays were carried out to characterize the susceptibility of sugarcane borer to the Bt toxin Cry1Ab and to select a resistant strain for additional studies on Cry1Ab resistance. Susceptibility was characterized by exposing neonates of different Brazilian colonies of sugarcane borer to different concentrations in meridic diet using surface application of Cry1Ab toxin. Selection for Cry1Ab resistance was carried out by exposing neonates to Cry1Ab-expressing maize (MON 810). The resistance of the borer populations to Cry1Ab was variable with LC50 and EC50 values reaching about 30-fold. The larvae responded positively to Cry1Ab selection exhibiting a 55-fold increase in resistance after four generations. This suggests the suitability of using leaves containing Bt-expressing genes for selection and the existence of variability of Bt-resistance in populations of the sugarcane borer.  相似文献   

9.
A three year (2003-2005) field study compared the susceptibility to the Cry1Ab toxin, expressed in Bt maize, of Mediterranean corn borer (MCB) Sesamia nonagrioides populations collected from areas with different adoption rates of Bt maize in Spain with Bt-free areas in Greece. Spain is the only European country where the cultivar Compa CB derived from the event Bt176 was commercially grown, from 1998 to 2005. The large decrease of the titer of the toxin in this cultivar at later growth stages represented the worst-case scenario for resistance development of MCB, since larvae of the second and third generations were exposed to sublethal concentrations of Cry1Ab toxin. Our data revealed that the variation in susceptibility to Cry1Ab for the MCB Spanish field populations analyzed in the three years was very low, with LC50 values fluctuating between 12 and 30 ng Cry1Ab/cm2, regardless of the region of origin, the type of maize (Bt or non-Bt) and the year. Furthermore, no significant differences were found when comparisons were made with a laboratory population (LC50 values: 18-26 ng Cry1Ab/cm2) or with field populations from Greece (Bt-free areas), which displayed LC50 values ranging between 22 and 27 ng Cry1Ab/cm2. Standardizing bioassay protocols proved to be essential for obtaining comparable results. These findings suggest that resistant MCB populations did not evolve in those Spanish maize areas where Compa CB was largely cultivated for eight years, contradicting the expected rapid development of resistance under these unfavourable conditions. Additionally, our results can be used as baseline indices in post-market resistance monitoring programs if Bt maize is introduced in Greece. Further studies should continue, since the insights gained from a resistance monitoring program may help to enhance the durability of Bt maize.  相似文献   

10.
Between 2002 and 2004, collections of egg masses of Asian corn borer (ACB), Ostrinia furnacalis (Guenée) were made from corn-planting sites on the major Philippine islands of Luzon (Laguna, Pangasinan, Camarines Sur and Isabela provinces) and Mindanao (Bukidnon and South Cotabato provinces). The resulting neonates were bioassayed for susceptibility to Bacillus thuringiensis (Bt) Cry1Ab protein. The median lethal concentrations (LC50s) for the different collections ranged from 0.42 to 2.37 ng/cm2. The bioassay results suggest that Philippine corn borer populations were highly susceptible to Cry1Ab protein prior to the widespread deployment of Bt corn. The upper limit of the estimated LC99 (104 ng/cm2) from the pooled bioassay data was selected as a candidate diagnostic concentration and subsequently tested on eleven ACB populations. Results of the validation assays showed that the mortality response of all the tested ACB populations was higher than the expected mortality (99%). Therefore, the concentration of 104 ng/cm2 was used to monitor susceptibility in ACB populations in the Philippines. Monitoring of field populations during 2009 in areas where Bt corn had been grown for 3 years found some enhanced survival of neonates at the diagnostic concentration but progeny of the diagnostic-concentration survivors did not survive on Bt corn, indicating that ACB populations in the Philippines remain susceptible to Cry1Ab-containing Bt corn hybrids.  相似文献   

11.
SmartStax® insect-protected corn (Zea mays L.) contains genes for six Bacillus thuringiensis (Bt) proteins controlling both lepidopteran pests and the corn rootworm complex (Diabrotica spp.). The properties of SmartStax, particularly the multiple effective modes of action (i.e., each Bt protein provides a high level of control of the target pests with a low probability of cross-resistance among the proteins), have provided the opportunity to add to previously approved structured refuge options by combining the non-Bt refuge seed with SmartStax seed in a seed mix. Seed mixes ensure that a refuge is present in every Bt field, remove concerns about grower compliance with refuge requirements, and provide grower convenience. However, seed mixes could increase the likelihood that larval insects move between Bt and non-Bt plants and vice versa. Assessing the insect resistance management (IRM) value of a seed mix refuge requires an assessment of the amount of larval movement, and the consequences of that movement, for the key target pests. The studies here present such data for control of corn rootworm by SmartStax corn, which contains the rootworm-active protein Cry3Bb1 and the binary protein Cry34Ab1/Cry35Ab1. In a growth chamber experiment, SmartStax was most effective against first instars and significantly effective against second instars, but did not control third instars. In a field study of movement from a heavily infested non-Bt plant onto surrounding plants, a larger percentage of insects successfully dispersed from the infested plant when the surrounding plants were non-Bt plants than when they were SmartStax plants. A paired-plant study showed that few larvae migrated from infested SmartStax plants and survived on nearby non-Bt plants; larvae that migrated from infested non-Bt plants had low survival if the adjacent plants were SmartStax. Replicated field studies of plant-to-plant movement indicated that the non-Bt plants in a 5% or 10% seed mix consistently supported large populations of susceptible insects and represented a productive refuge, whereas the SmartStax plants had few or no survivors. The timing of emergence from seed mix plots containing 5% or 10% non-Bt plants was more similar to that of the non-Bt plots than that of the SmartStax plots. Thus, the available growth chamber and field data indicate that a seed mix of 5% or more will provide an effective refuge for corn rootworm in SmartStax corn.  相似文献   

12.
An alternative to traditional larval lepidopteran resistance-monitoring bioassays was developed. Feeding disruption tests were developed for detecting insects resistant to three Bacillus thuringiensis (Bt) proteins: Cry1Ac, Cry1F and Cry1Ab. The assays rely on a diagnostic dose of Bt toxin in 100-μl hydratable meal pads of artificial diet containing blue indicator dye. The assay was formatted as a portable (palm-sized) plastic plate containing an array of 16 test wells, each containing a single hydratable meal pad with one insect added per well. The diagnostic dose was the concentration of Bt in meal pad rehydration solution that reduced 24 h dyed fecal production of Bt-susceptible neonates to ≤2 fecal pellets per larva. Bt-resistant neonates were able to consume the diagnostic dose of the insecticidal protein and produce >2 blue fecal pellets. The feces were distinctly visible on the white background of the feeding disruption test plate. Diagnostic doses were determined with lab-strain Bt-susceptible Heliothis virescens and Helicoverpa zea. For H. virescens, the diagnostic doses were 10, 20 and 15 μg/ml for Cry1Ac, Cry1F and Cry1Ab, respectively. For H. zea, the diagnostic doses were 40, 200 and 500 μg/ml, respectively. The assays were validated against a lab-strain of Bt-resistant H. virescens and with susceptible larval H. virescens collected as eggs from field-grown tobacco in North Carolina.  相似文献   

13.
The inclusion of the cry gene in corn may produce direct effects on non-target pests. Our research was focused on the relationship between Bt corn germplasm, expressing the cry1F protein to control the fall armyworm [Spodoptera frugiperda (Noctuidae)], and a non-target pest, the corn leafhopper [Dalbulus maidis (Cicadellidae)]. The aim of this contribution was to elucidate if Bt corn plants have influence on the oviposition preference of the leafhopper and to evaluate the effect of the transgenic plant on the hatching rate of egg. Female corn leafhoppers were released in cages each containing two potted plants in the V2 stage: a Bt germplasm and the corresponding isogenic hybrid. Laid eggs were counted and the number of hatched nymphs recorded. D. maidis females oviposited and laid more eggs in Bt plants. The egg hatching rate was negatively affected by the Bt germplasm. In addition, a field study was conducted in order to determine the abundance of D. maidis adults in Bt corn and the corresponding non-Bt isoline. Two corn plots sown with the same germplasms as used in the laboratory bioassays were sampled weekly. In the field, the population of the corn leafhopper was higher in the Bt corn plot than in the non-Bt isoline. Possible hypotheses for the differences in abundance of the vector in the field are: a) that pleiotropic effects of Bt corn could attract adults; b) the existence of a possible direct competition between the corn leafhopper and the target pest in order to utilize the whorls of corn plants as refuge and feeding sites, so the high populations of the vector could be due to the large supply of healthy whorls in the transgenic plot; and/or c) a differential attack of natural enemies occurring in non-Bt plots.  相似文献   

14.
Susceptibility of Chilo partellus (Lepidoptera, Crambidae) and Busseola fusca (Lepidoptera, Noctuidae) populations to Cry proteins from the bacterium, Bacillus thuringiensis (Bt), the δ-endotoxins Cry1Ab and Cry1Ba in Bt-maize, were evaluated under biosafety greenhouse conditions. Larval feeding on Bt-maize was adjusted to deliver sub-lethal doses of δ-endotoxins from the two events; survivors were reared on artificial diet to obtain successive generations. Eight generations of three C. partellus populations and five generations of a B. fusca population were screened for susceptibility on each event. Mean proportion of surviving larvae from Bt-maize plants, and the corresponding pupal weights of survivors for each population, were lower for individuals exposed to δ-endotoxins. Both Bt Cry proteins expressed in maize leaves controlled C. partellus and showed stability in control, with no indication of a change in susceptibility among generations. Neither toxin, however, provided complete control of B. fusca, but no changes in susceptibility were observed after five generations of selection. Implications for development of future transgenic Bt maize events, and research for East Africa are discussed.  相似文献   

15.
Fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major pest of many crops and a cross-crop target of transgenic maize, cotton, and soybean containing Bacillus thuringiensis (Bt) genes. Some of the current Bt maize products for controlling lepidopteran species contain the Bt event MON 89034. The objective of this study was to determine the frequency of resistance alleles in field populations of S. frugiperda collected from Louisiana and Florida, U.S. to Cry1A.105, one of the two Bt genes in MON 89034. A total of 150 F2 two-parent families of S. frugiperda were established using single-pair mating of field-collected individuals in 2011, which included 79 families from two locations in Louisiana and 71 families from one location in Florida. F2 screen was conducted to detect resistance alleles in these families to Cry1A.105 protein in maize plants. Four out of the 79 Louisiana and 14 out of the 71 Florida families were identified to possess resistance alleles to the Cry1A.105 maize plants. Thus, the corresponding frequency of resistance alleles to Cry1A.105 maize was estimated to be 0.0158 with a 95% credibility interval (CI) of 0.0052–0.0323 for the Louisiana populations and 0.0559 with a 95% CI of 0.0319–0.0868 for the Florida populations. The resistant families survived on whole Cry1A.105 maize plants and demonstrated a significant level (>116-fold) of resistance to the Cry1A.105 protein in a diet-incorporated bioassay. These findings suggest that resistance allele frequency in S. frugiperda to single-gene Cry1A.105 maize in the U.S. southeast region apparently is not rare, most likely due to the selection of Cry1F resistance and its cross-resistance to Cry1A.105.  相似文献   

16.
Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a key insect pest of cotton in the Henan cotton growing region of China. In this region, cotton is grown on small acreages in rich agricultural landscapes, contrary to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt plants) may be sufficient to prevent H. armigera resistance development to Bt toxins. In order to gain a timely understanding of the evolution of resistance of H. armigera to Bt toxin after continuous cultivation of Bt cotton for c. 10 years, we assessed the frequency of alleles conferring resistance to Cry1Ac toxin in field populations of H. armigera sampled from Xinxiang County in Henan province during 2007-2009. Screening F1 and F2 generations from isofemale lines, derived from female moths trapped in the field, were used with a discriminating dose of Cry1Ac diet to estimate the frequency of resistance alleles. Totals of 625, 516 and 488 isofemale lines were screened for the F1 generation in 2007, 2008 and 2009, respectively. Resistance gene frequency in Xinxiang fluctuated between 0.0000 and 0.0005, and it did not increase significantly from 2007 to 2009. Based on the relative average development rates (RADR) of H. armigera larvae in F1 tests, no substantial increase in Cry1Ac tolerance was found in the Xinxiang region over the 3-yr period.  相似文献   

17.
Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a serious pest of cotton and many other crops in northern China. To evaluate the contribution of alternative hosts as an effective refuge for transgenic cotton expressing the Bacillus thuringiensis (Bt) Cry1Ac toxin, the susceptibility to this toxin was measured in progeny derived from field-collected H. armigera larvae and pupae from different hosts in the Xiajin’s region of the Shandong Province in northern China. During 2008-2010, progeny from a total of 258,56,184 and 160 single-pair crosses derived from wheat (first-generation), Bt cotton (second-generation), Bt cotton (third-generation), and corn (third-generation) were screened on Cry1Ac diets, respectively. Based on relative average development rates (RADR) of H. armigera larvae in these F1 tests, the second and third-generation moths emerging from Bt cotton fields were more tolerant to the Bt toxin than the first and third-generation moths emerging from wheat and corn each year. These results suggest that there is significant variation in susceptibility to Bt toxins among H. armigera populations derived from different host crops. Alternate crops, such as corn, that maintain Bt susceptible populations of H. armigera could be used as refugia to minimize the evolution of resistance to Bt cotton.  相似文献   

18.
This paper documents the historical development of resistance of the African maize stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae) to Bt maize (Zea mays L.). This pest was one of the first to evolve resistance to Bt maize expressing Cry1Ab protein. A time-line of events and contributing factors are presented, from the commencement of efficacy testing through to the present situation, where the Cry1Ab toxin has lost its efficacy against B. fusca at many localities throughout the maize producing region, and single-gene Bt maize events often require insecticide treatments for which farmers are compensated. Significant levels of pest survival on Bt maize was observed in the first season after commercial release in 1998 and confirmed seven years later. Reduced selection pressure on the target pest is the objective of insect resistance management (IRM), and strategies to accomplish this should receive highest priority. Where resistance is prevalent, the only viable options to reduce selection pressure are withdrawal of the product and/or enforcement of high-dose/refuge requirements. The latter action may however be of no value under conditions where resistance is prevalent, since the value of refugia to an IRM strategy may be compromised. Remedial actions taken in South Africa included the propagation and enforcement of refuge compliance followed by the release of pyramided maize hybrids in 2011. These pyramids combine Cry1A.105 and Cry2Ab2 toxin-producing transgenes, replacing the ineffective single-transgene. However, it remains uncertain if cross-resistance occurs between Cry1A.105/Cry2Ab2 and the closely related Cry1Ab toxin, and for how long this pyramided event will endure. Cultivation of Cry1Ab-expressing hybrids continues in areas where resistance levels have been confirmed to be high. In retrospect, this case provides lessons regarding IRM, not only in South Africa, but wherever Bt crops are being introduced.  相似文献   

19.
应用单管巢式和半巢式PCR检测转基因玉米MON89034   总被引：1，自引：1，他引：0  
根据MON89034玉米的5’端和3’端边界序列分别设计1组转化体特异性的巢式PCR引物,采用中途进退式PCR策略建立MON89034玉米的转化体特异性检测方法,扩增产物分别为491 bp和188 bp。以转基因玉米MON89034及8种其他转基因作物为材料,证明此方法对MON89034玉米具有高度特异性。灵敏度测试结果表明,此方法的相对检出限达到0.01%,绝对检出限为4个单倍体基因组拷贝数,比普通PCR提高了5倍。建立的单管巢式和半巢式PCR方法可准确、高效地检测转基因玉米MON89034及其产品。  相似文献   

20.
A concern regarding planting of Bt crops is that their widespread cultivation could lead to evolution of insect resistance to Bt toxins. In South Africa, the noctuid maize stem borer (Busseola fusca [Fuller]), is resistant to Bt maize (Zea mays L.; MON810) which produces Cry1Ab protein. The presence of fitness costs in resistant populations could be a valuable component of resistance management since the non-Bt maize refuge may select against resistance. The aim of the study was to determine if there are fitness costs associated with Bt resistance of B. fusca. Life history parameters were compared between individuals of a Bt maize resistant B. fusca population when feeding on Bt or non-Bt maize. Similar comparisons were done using a control population. Field collected larvae as well as their F1-generation were used in the study. The following parameters were compared: pupal mass, moth longevity, fecundity, fertility, larval mass and survival, and sex ratio. Except for LT50-values, no fitness costs were associated with the resistance trait in the highly resistant B. fusca population. The absence of fitness costs and presence of resistant populations may promote the use of a multi-gene strategy which would be expected to impact negatively on fitness.  相似文献   

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