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1.
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   

2.
Studies on the influence of genotypic resistance on biological activity of a commercial formulation of Bacillus thuringiensis (Bt) and pure Bt toxin Cry1Ac were carried out to develop appropriate strategies for pod borer, Helicoverpa armigera management in chickpea, sorghum, pigeonpea and cotton. The interaction effects of host plant resistance and biological activity of commercial Bt/Cry1Ac were studied by incorporating the lyophilized tissues of chickpea leaves, milk stage sorghum grain, pigeonpea pods and cotton squares into the artificial diet with and without Bt formulation or Cry1Ac. The H. armigera larval weights were significantly lower in insects reared on diets with square powder of the insect - resistant Bt-cotton RCH 2 + Bt/Cry1Ac and pod powder of insect - resistant pigeonpea genotype, ICPL 332WR + Bt/Cry1Ac as compared to the larvae reared on diets with leaf powder of H. armigera susceptible chickpea genotype, ICCC 37 and the standard artificial diet. Pupation and adult emergence were significantly lower in insects reared on diets with tissues of pod borer-resistant genotypes + Bt/Cry1Ac as compared to insects reared on diets with tissues of the insect susceptible genotypes + Bt/Cry1Ac. Insects reared on diets containing insect-resistant and -susceptible genotypes of sorghum, pigeonpea and cotton and pod borer-resistant genotype of chickpea (ICC 506EB) + Bt/Cry1Ac did not lay any eggs. However, eggs were laid by the insects reared on diets containing pod borer-susceptible genotype of chickpea, ICCC 37 and on the standard artificial diet + Bt/Cry1Ac. The insects reared on diets with sorghum genotype, ICSV 745, and Bt-cotton, RCH 2 without Bt/Cry1Ac also did not lay eggs. The results suggested that Bt/Cry1Ac is more effective for management of H. armigera when deployed in combination with insect-resistant genotypes of cotton, chickpea, pigeonpea and sorghum.  相似文献   

3.
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   

4.
Seven-day laboratory bioassays with first-instar Helicoverpa armigera and Helicoverpa punctigera larvae were conducted using leaves from field-grown Bollgard II® cotton during the 2009/10 season and larval mortality and development recorded. Leaves were from three farms in the St George region and two fields on one farm at Emerald in eastern Australia. The Cry1Ac and Cry2Ab content of leaves from the same samples was determined (see Knight et al., 2013) and the relationships between Cry protein content and larval mortality and development were examined. The Cry1Ac protein content was between 3.98 and 12.08 μg/g during the growing season, while Cry2Ab content ranged between 300.6 and 953.3 μg/g. Cry1Ac and Cry2Ab content of leaves were highly correlated (r = 0.8276, P < 0.001). Seven-day mortality of H. punctigera larvae was close to 100% throughout the season. H. armigera mortality was close to 100% early in the season, but fell to ∼65% by mid-to late February in the laboratory bioassays. Fitting three-dimensional non-linear models associating Cry1Ac and Cry2Ab content with H. armigera and H. punctigera mortality elucidated the relative importance of the two proteins in determining larval mortality; for this analysis, data were pooled with data from an isoline study to provide better sampling of the three-dimensional surface being modelled. For both Helicoverpa species, the fitted mortality response to the Cry1Ac protein was close to its maximum at protein concentrations above ∼3 μg/g Cry1Ac. For H. punctigera, response to the Cry2Ab protein was close to maximal once Cry2Ab was greater than ∼200 μg/g. In contrast, the fitted H. armigera mortality response to Cry2Ab increased steadily with concentration up to ∼1200 μg/g Cry2Ab. These responses led to markedly different response surfaces for the two species; H. punctigera mortality was close to 100% at most places on the response surface, while for H. armigera the response surface showed stronger increases in mortality with concentration for Cry2Ab than for Cry1Ac. These results can be interpreted as meaning that at the plant-expressed range of concentrations in Bollgard II cotton the two proteins are approximately equally important for H. punctigera but that changes in Cry2Ab content more strongly influences changes in larval mortality in H. armigera than does Cry1Ac, with Cry1Ac contributing a consistent 40–45% mortality for concentrations above 3 μg/g. For H. armigera, there was no evidence of either synergism or antagonism between Cry1Ac and Cry2Ab proteins (P > 0.05) but this aspect was not testable for H. punctigera because mortality was mostly close to 100%.  相似文献   

5.
Bollgard® and BollgardII® cotton cultivars were evaluated for their efficacy for control of bollworms and their effects on sucking insects and the abundance of natural enemies under bollworm insecticide protected and non-insecticide protected field conditions during the 2004 and 2005 cropping seasons. Bollgard cultivars are genetic transforms that produce Cry1Ac toxins from Bacillus thuringiensis (Bt) to control American bollworm, Helicoverpa armigera. Second generation BollgardII cultivars contain 2 toxins, Cry1Ac and Cry2Ab, and are more effective in controlling a broader range of caterpillar species. Bollgard cultivars were free of H. armigera damage until harvest under insecticide protected as well as non-protected conditions. Both BollgardII and Bollgard cultivars were infested with larvae of spotted bollworm, Earias vitella, and spiny bollworm, Earias insulana, at later crop growth stages. Neither BollgardII nor Bollgard cultivars were free of square (fruiting body), open boll and loculi damage. Bollworm damage did not reach economic threshold levels up to harvest. Densities of sucking insects (Amrasca biguttula biguttula, Bemisia tabaci, Aphis gossypi, and Thrips tabaci), of the foliage feeder Myllocerus undecimpustulatus and of predators (Chrysoperla spp., Orius spp., Coccinella spp., Brumus spp., Vespa spp., Lycosa spp., and Aranews spp.) were similar on Bollgard, BollgardII and conventional cultivars. The time of the first appearance of bollworms, sucking insects and predators on Bt cotton did not vary from conventional cotton varieties. Insecticidal protection based on economic threshold levels resulted in significant reductions in bollworm damage on conventional cultivars.  相似文献   

6.
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   

7.
Transgenic Bt (Bacillus thuringiensis) cotton has been effectively used to control the cotton bollworm, Helicoverpa armigera (Hübner) in China. However, in recent years, following the wide commercialization of Bt cotton in northern China there have been frequent outbreaks of the non-target pest Apolygus lucorum (Meyer-Dür). To clarify how transgenic cotton contributes to these outbreaks, a four-year field investigation of population dynamics and laboratory life table studies were carried out from 2007 to 2010 to evaluate the impact of two transgenic cotton cultivars (SGK321 expressing Cry1Ac + CpTI and GK12 expressing Cry1Ac) and their corresponding parental non-transgenic lines (Shiyuan321 and Simian3) on A. lucorum. There were no significant differences in the population densities of A. lucorum found in Bt cotton and non-Bt cotton plots, whether one compared those that had received insecticide treatments or those that had not. However, population densities of A. lucorum were significantly lower in pesticide treated plots than in controls. Furthermore, there were no significant differences in the net reproductive rates, generation times or intrinsic rates of increase of A. lucorum when reared on either Bt or non-Bt cotton cultivars. These results suggest that Bt cotton has no direct positive or negative effects on the biology of A. lucorum, so the most logical explanation for the observed outbreaks is the decrease in pesticide applications following the commercial release of Bt cotton.  相似文献   

8.
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   

9.
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   

10.
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   

11.
Large-scale adoption of transgenic crops expressing genes from Bacillus thuringiensis (Bt) imposes high selection pressure for evolution of field-relevant resistance that can reduce pest control efficacy, such as reported for Cry1F maize (Zea mays L.) in populations of fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), of Puerto Rico, Brazil, and the United States. As part of our effort to improve fall armyworm resistance management to Bt crops, here we determined the genetic basis of Cry1F resistance in two S. frugiperda strains originated from field collections in different regions of Brazil and further selected in the laboratory for high levels of resistance to Cry1F maize. Continuous exposure to the TC1507 event for 11 generations resulted in more than 183-fold resistance to Cry1F in the two strains studied, and such a high resistance level enabled the insects to complete larval development on the Bt maize plants. Genetic analyses using concentration-response bioassays with progenies from reciprocal crosses between resistant and susceptible insects indicated that the inheritance of the resistance is autosomal, recessive and without maternal effects. Backcross of the F1 progeny with the parental resistant strains revealed that the resistance in the two selected strains is conferred by a single locus or set of tightly linked loci. These results support some of the assumptions of the strategy in use for fall armyworm resistance management to Bt Cry1F maize, but survival rates of heterozygotes on the Bt plants were higher than 5%, showing that the Cry1F maize does not produce a high dose of the insecticidal protein for S. frugiperda. Additionally, we detected a delay in larval development time that may favor assortative mating of individuals carrying resistance alleles. These findings are consistent with the rapid evolution of Cry1F resistance in certain field populations of fall armyworm. Implications for resistance management of S. frugiperda to Bt maize are discussed.  相似文献   

12.
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   

13.
Helicoverpa armigera is the key pest of cotton in Spain, resulting in many insecticide treatments against it. The resistance status of H. armigera to different insecticides currently used in cotton was evaluated in Spain in two different seasons, 1999 and 2004. Four populations were tested in total, two in each season. Toxicological bioassays were conducted in the laboratory, and performed on third instar larvae by topical application of the insecticides. LD50's were estimated by probit analysis and resistance factors (RF) were calculated at the LD50 level. Four insecticides were evaluated, but only endosulfan reached a moderate resistance level (RF = 11.4), and the others (methomyl, chlorpyrifos and lambda-cyhalothrin) showed low resistance (RF between 1.9 and 6.0). Such results indicate the generally low resistance of H. armigera to most of the insecticides used against this pest in cotton in Spain. Possible explanations for this situation are discussed.  相似文献   

14.
Bollgard II cotton has been grown commercially in Australia since 2003 for control of the primary target species Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) Larvae of both species have been reported to survive at low frequencies on Bollgard II with larvae >8 mm recorded in between 7 and 18% of the area planted to Bollgard II cotton between 2005/06 and 2007/08. F1 and F2 tests have shown that this is not due to the presence of resistance genes in the surviving larvae. To understand if fluctuations in the expression of the Cry proteins in Bollgard II allow some larvae to survive, plant tissue samples were taken from five Bollgard II cultivars throughout the growing season within fields and from different farms within a production region between 2007 and 2010. The data indicate that the expression of both Cry proteins is similar to the known resistance-monitoring diagnostic concentrations and relatively uniform between fields within a farm and between farms within a region, with less than one-third of the tests at this level of variation being significant. However, there were intra-seasonal changes in expression of both Cry proteins and differences in expression between plant structures and between cultivars for both Cry proteins. Further work is needed to establish if this variation in Cry protein content in Bollgard II cotton affects the control of Helicoverpa spp. in the field or whether plant-physiological and pest-behavioural factors underlie the occasional occurrence of Helicoverpa larval survival on Bollgard II cotton.  相似文献   

15.
Multiple independent trials were conducted to evaluate the performance of Cry1Ab-susceptible (Cry1Ab-SS), -heterozygous (Cry1Ab-RS), and -resistant (Cry1Ab-RR) genotypes of the sugarcane borer, Diatraea saccharalis (F.), on eight commercial hybrids and six experimental corn lines. The commercial varieties included two non-Bt and six Bt corn hybrids that expressed a single Bt protein (either Cry1Ab or Cry1F) targeting above-ground lepidopteran pests. The six experimental lines consisted of two non-Bt and four Bt corn lines, two expressing just the Cry1Ab protein and two containing the pyramided-genes Cry1A.105 and Cry2Ab2 (event MON 89034). Larval mortality on non-Bt corn leaf tissue ranged from 6 to 45% after 12 d across insect genotypes. The 12 d mortality of Cry1Ab-SS on leaf tissue of commercial Cry1Ab or Cry1F corn was 96-100%, whereas it was 80-96% for Cry1Ab-RS and 68-78% for Cry1Ab-RR. On intact plants, 39-64% of larvae survived on non-Bt corn plants after 21-25 d. Larval survivorship on intact plants of commercial Cry1Ab or Cry1F corn was 0-8.1% for Cry1Ab-SS, 1.3-34% for Cry1Ab-RS, and 19-51% for Cry1Ab-RR. Larvae of Cry1Ab-RR and -RS also caused significant plant injury to most of the commercial Bt corn hybrids, especially to the Cry1Ab corn. Cry1Ab resistance in D. saccharalis was incompletely dominant on commercial Bt corn hybrids. However, both experimental lines with pyramided genes of Cry1A.105 and Cry2Ab2 provided complete control of all three insect genotypes in both leaf tissue and intact plant tests. Results of this study suggest that MON 89034 should offer a means for Bt resistance management in D. saccharalis.  相似文献   

16.
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   

17.
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   

18.
In sub-Saharan areas of Africa, cotton growers no longer cut the shoot tips from plants (topping), although manual topping was promoted at the start of the 20th century to improve yield and, surprisingly, to reduce pest incidence. In these areas, the bollworms Helicoverpa armigera Hübner, Earias spp., and Diparopsis watersi Rothschild are responsible for the majority of cotton yield losses, and the use of pyrethroids has resulted in resistance in field populations of H. armigera. In the face of these problems and given the scarcity of literature on the effects of topping on pest control, we assessed bollworm infestation levels in 12 trials comparing manual topping and non-topping cotton plots in Mali over a six-year period (2002, 2003, and 2005 to 2008). Topping was performed at the emergence of the 15th sympodial branch or at 10 days after the first flower opening. Our results showed no significant difference in seed cotton yields between topped and non-topped cotton. Bollworm infestations (all species) were always lower on topped cotton and 7 out of 12 trials showed significantly lower infestations on topped cotton. In plots of topped cotton, we recorded an average of 56% fewer H. armigera larvae, 68% fewer Earias spp. larvae, and 71% fewer D. watersi larvae with respectively 5, 4, and 3 out of 12 trials with significant differences in favor of topping and no significant difference in favor of non-topping. To our knowledge, our study is the first to report decreases in D. watersi larval infestation with cotton topping. Further studies are required to understand the mechanisms involved in these effects and to ensure that topping is economically attractive for farmers.  相似文献   

19.
The Cry1F protein from Bacillus thuringiensis Berliner expressed in event TC1507 maize (Zea mays L.) was one of the most effective ways to control Spodoptera frugiperda (J. E. Smith) in Brazil. After reports of reduced effectiveness of this Bt maize event in some areas of Brazil, research was undertaken to investigate if damage to Cry1F maize was caused by resistant S. frugiperda. Additional investigations were conducted to evaluate the genetic basis of the resistance and to test if Cry1F resistant S. frugiperda selected from populations of different regions of Brazil share the same resistance locus by using complementation tests. Neonate larvae of S. frugiperda collected from TC1507 maize fields with damage in Western Bahia region in 2011 were able to survive on Cry1F maize plants under laboratory conditions and subsequently produced normal adults. Survival of Cry1F-susceptible S. frugiperda on non-Bt maize was significantly higher in leaf than plant bioassays. Resistance ratio in diet overlay bioassays was >5000-fold. A discriminating concentration of 2000 ng cm−2 of Cry1F protein was defined for monitoring the frequency of resistance of S. frugiperda to Cry1F. Cry1F resistant S. frugiperda showed a recessive autosomal inheritance for alleles involved in resistance to Cry1F protein. In complementation tests, the resistant population from Western Bahia was crossed with the other seven resistant populations collected from different States of Brazil. F1 larvae from each cross had the same survival at discriminating concentration of 2000 ng cm−2 of Cry1F protein, indicating that the resistance alleles in each population were likely at the same locus. Therefore, implementation of resistance management strategies is urgent to prolong the lifetime of Cry1F for controlling S. frugiperda in Brazil.  相似文献   

20.
Spodoptera cosmioides (Walker), Spodoptera eridania (Stoll) and Spodoptera frugiperda (J. E. Smith) have caused significant damage on soybean Glycine max (L.) Merrill in Brazil. Genetically-modified MON 87701 × MON 89788 soybean that expresses the Cry1Ac protein is potentially an alternative tool for the management of these species. Purified protein bioassays were done to evaluate the susceptibility of S. cosmioides, S. eridania and S. frugiperda to Cry1Ac protein. The level of efficacy of the Bt soybean plants in controlling these species was measured through laboratory and greenhouse trials under high artificial insect infestations. The biology of these insects was evaluated over their development cycles to understand their life history when fed on Bt soybean. Purified Cry1Ac protein at the maximum concentration tested (100 μg Cry1Ac mL−1 diet) resulted in low mortality of S. cosmioides and S. eridania (<13%) and intermediate mortality of S. frugiperda (50%). No significant effects of the Bt soybean plants were observed in the life table parameters of S. cosmioides and S. eridania. However, S. frugiperda fed on Bt soybean plants had a prolonged larval stage (by 5 days), reduced larvae viability, increased mean generation time (by 8 days) and reduced intrinsic rate of increase. In general, the Bt soybean plants showed poor control of Spodoptera species when evaluated by leaf-disc bioassay and greenhouse trials. Consequently, other control tactics must be used in combination with MON 87701 × MON 89788 soybean in the field for the efficient management of S. cosmioides, S. eridania and S. frugiperda.  相似文献   

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