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

Daniel Bernardi,Patrick Marques Dourado,Renato Assis Carvalho,Oderlei Bernardi,Renato Jun Horikoshi,Samuel Martinelli,Eloisa Salmeron,Celso Omoto,Graham P Head

doi:10.1371/journal.pone.0140130

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.

Highlights

Agriculture in tropical regions poses a number of challenges relative to temperate zones primarily due to the longer growing seasons and absence of freezing winter temperatures [1]
Fall armyworm field populations were sampled across Brazil in 2012
Insects collected on maize expressing Cry1F protein resulted in 41 positivefamilies identified by testing on MON 89034 leaf tissues

Summary

Introduction

Agriculture in tropical regions poses a number of challenges relative to temperate zones primarily due to the longer growing seasons and absence of freezing winter temperatures [1]. Insects collected on maize expressing Cry1F protein (population BA27) resulted in 41 positive (resistance alleles-containing) (iso)families identified by testing on MON 89034 leaf tissues. These results indicated the potential for cross-resistance in S. frugiperda between Cry1F and Cry1A.105, one of the two Bt proteins expressed by MON 89034 maize.

Results

Conclusion