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Cross-Resistance between Cry1 Proteins in Fall Armyworm (Spodoptera frugiperda) May Affect the Durability of Current Pyramided Bt Maize Hybrids in Brazil.

Bernardi D, Salmeron E, Horikoshi RJ, Bernardi O, Dourado PM, Carvalho RA, Martinelli S, Head GP, Omoto C - PLoS ONE (2015)

Bottom Line: Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found.Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively.Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology and Acarology, Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ/USP), Piracicaba, São Paulo, Brazil.

ABSTRACT
Genetically modified plants expressing insecticidal proteins from Bacillus thuringiensis (Bt) offer valuable options for managing insect pests with considerable environmental and economic benefits. Despite the benefits provided by Bt crops, the continuous expression of these insecticidal proteins imposes strong selection for resistance in target pest populations. Bt maize (Zea mays) hybrids have been successful in controlling fall armyworm (Spodoptera frugiperda), the main maize pest in Brazil since 2008; however, field-evolved resistance to the protein Cry1F has recently been reported. Therefore it is important to assess the possibility of cross-resistance between Cry1F and other Cry proteins expressed in Bt maize hybrids. In this study, an F2 screen followed by subsequent selection on MON 89034 maize was used to select an S. frugiperda strain (RR) able to survive on the Bt maize event MON 89034, which expresses the Cry1A.105 and Cry2Ab2 proteins. Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found. The RR strain showed high levels of resistance to Cry1F, which apparently also conferred high levels of cross resistance to Cry1A.105 and Cry1Ab, but had only low-level (10-fold) resistance to Cry2Ab2. Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively. Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil. Nevertheless, the occurrence of Cry1F resistance in S. frugiperda across Brazil, and the cross-resistance to Cry1Ab and Cry1A.105, indicates that current Cry1-based maize hybrids face a challenge in managing S. frugiperda in Brazil and highlights the importance of effective insect resistance management for these technologies.

No MeSH data available.


Related in: MedlinePlus

Concentration-response of S. frugiperda in diet-overlay bioassays with purified Cry1A.105 (A and B) and Cry2Ab2 (C and D) proteins.Each data point represents the mean of four replicates, corrected for control mortality. Error bars represent SD.
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pone.0140130.g001: Concentration-response of S. frugiperda in diet-overlay bioassays with purified Cry1A.105 (A and B) and Cry2Ab2 (C and D) proteins.Each data point represents the mean of four replicates, corrected for control mortality. Error bars represent SD.

Mentions: To understand the resistance patterns observed in the F2 screen on MON 89034 leaf tissue, the RR strain was characterized using diet-overlay bioassays with purified Cry1A.105 and Cry2Ab2 proteins (Table 3; S3 Table). The RR strain had more than 3,300-fold resistance to Cry1A.105 (MIC50 > 16,000 ng/cm2) relative to the SS strain. In contrast, a low level of resistance (10-fold) was observed for Cry2Ab2 relative to the SS strain (Table 3; S3 Table), which may only have reflected the greater vigor of the field-derived RR strain compared with the laboratory-reared SS strain. The MIC50, a concentration that inhibits 50% of larvae from molting to second instar after 7 days, for Cry1A.105 tested against the RR strain could not be precisely determined because 50% mortality was never achieved, even at the highest concentration (Fig 1; S4 Table). Using a Cry1A.105 stock solution of 1,000 μg/ml, it was possible to generate a maximum concentration of 16,000 ng/cm2 of diet in the overlay bioassay; consequently, the MIC50 for Cry1A.105 must be greater than 16,000 ng/cm2. The resistance ratio of the RR strain tested on Cry1A.105 was much lower when based on larval growth inhibition (EC50) (207-fold), indicating some level of Cry1A.105 activity against the RR strain (Table 3; Fig 1). Both heterozygous strains (reciprocal crosses) showed similar MIC50 values, ranging from 25.05 to 32.62 ng/cm2 for Cry1A.105 and from 45.63 to 48.35 ng/cm2 for Cry2Ab2 (Table 3; S3 Table). The MIC50 and EC50 of both heterozygous strains with Cry1A.105 were significantly lower than those of the RR strain, and higher than those of the SS strain (Table 3; S3 Table). With the exception of the EC values for Cry1A.105, the overlapping confidence limits for the MIC and EC values of the reciprocal F1 crosses between the SS and RR strains (S♂R♀, S♀R♂) indicated autosomal inheritance of the resistance trait in the RR strain.


Cross-Resistance between Cry1 Proteins in Fall Armyworm (Spodoptera frugiperda) May Affect the Durability of Current Pyramided Bt Maize Hybrids in Brazil.

Bernardi D, Salmeron E, Horikoshi RJ, Bernardi O, Dourado PM, Carvalho RA, Martinelli S, Head GP, Omoto C - PLoS ONE (2015)

Concentration-response of S. frugiperda in diet-overlay bioassays with purified Cry1A.105 (A and B) and Cry2Ab2 (C and D) proteins.Each data point represents the mean of four replicates, corrected for control mortality. Error bars represent SD.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608726&req=5

pone.0140130.g001: Concentration-response of S. frugiperda in diet-overlay bioassays with purified Cry1A.105 (A and B) and Cry2Ab2 (C and D) proteins.Each data point represents the mean of four replicates, corrected for control mortality. Error bars represent SD.
Mentions: To understand the resistance patterns observed in the F2 screen on MON 89034 leaf tissue, the RR strain was characterized using diet-overlay bioassays with purified Cry1A.105 and Cry2Ab2 proteins (Table 3; S3 Table). The RR strain had more than 3,300-fold resistance to Cry1A.105 (MIC50 > 16,000 ng/cm2) relative to the SS strain. In contrast, a low level of resistance (10-fold) was observed for Cry2Ab2 relative to the SS strain (Table 3; S3 Table), which may only have reflected the greater vigor of the field-derived RR strain compared with the laboratory-reared SS strain. The MIC50, a concentration that inhibits 50% of larvae from molting to second instar after 7 days, for Cry1A.105 tested against the RR strain could not be precisely determined because 50% mortality was never achieved, even at the highest concentration (Fig 1; S4 Table). Using a Cry1A.105 stock solution of 1,000 μg/ml, it was possible to generate a maximum concentration of 16,000 ng/cm2 of diet in the overlay bioassay; consequently, the MIC50 for Cry1A.105 must be greater than 16,000 ng/cm2. The resistance ratio of the RR strain tested on Cry1A.105 was much lower when based on larval growth inhibition (EC50) (207-fold), indicating some level of Cry1A.105 activity against the RR strain (Table 3; Fig 1). Both heterozygous strains (reciprocal crosses) showed similar MIC50 values, ranging from 25.05 to 32.62 ng/cm2 for Cry1A.105 and from 45.63 to 48.35 ng/cm2 for Cry2Ab2 (Table 3; S3 Table). The MIC50 and EC50 of both heterozygous strains with Cry1A.105 were significantly lower than those of the RR strain, and higher than those of the SS strain (Table 3; S3 Table). With the exception of the EC values for Cry1A.105, the overlapping confidence limits for the MIC and EC values of the reciprocal F1 crosses between the SS and RR strains (S♂R♀, S♀R♂) indicated autosomal inheritance of the resistance trait in the RR strain.

Bottom Line: Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found.Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively.Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology and Acarology, Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ/USP), Piracicaba, São Paulo, Brazil.

ABSTRACT
Genetically modified plants expressing insecticidal proteins from Bacillus thuringiensis (Bt) offer valuable options for managing insect pests with considerable environmental and economic benefits. Despite the benefits provided by Bt crops, the continuous expression of these insecticidal proteins imposes strong selection for resistance in target pest populations. Bt maize (Zea mays) hybrids have been successful in controlling fall armyworm (Spodoptera frugiperda), the main maize pest in Brazil since 2008; however, field-evolved resistance to the protein Cry1F has recently been reported. Therefore it is important to assess the possibility of cross-resistance between Cry1F and other Cry proteins expressed in Bt maize hybrids. In this study, an F2 screen followed by subsequent selection on MON 89034 maize was used to select an S. frugiperda strain (RR) able to survive on the Bt maize event MON 89034, which expresses the Cry1A.105 and Cry2Ab2 proteins. Field-collected insects from maize expressing the Cry1F protein (event TC1507) represented most of the positive (resistance allele-containing) (iso)families found. The RR strain showed high levels of resistance to Cry1F, which apparently also conferred high levels of cross resistance to Cry1A.105 and Cry1Ab, but had only low-level (10-fold) resistance to Cry2Ab2. Life history studies to investigate fitness costs associated with the resistance in RR strain revealed only small reductions in reproductive rate when compared to susceptible and heterozygous strains, but the RR strain produced 32.2% and 28.4% fewer females from each female relative to the SS and RS (pooled) strains, respectively. Consistent with the lack of significant resistance to Cry2Ab2, MON 89034 maize in combination with appropriate management practices continues to provide effective control of S. frugiperda in Brazil. Nevertheless, the occurrence of Cry1F resistance in S. frugiperda across Brazil, and the cross-resistance to Cry1Ab and Cry1A.105, indicates that current Cry1-based maize hybrids face a challenge in managing S. frugiperda in Brazil and highlights the importance of effective insect resistance management for these technologies.

No MeSH data available.


Related in: MedlinePlus