title: High susceptibility and low resistance allele frequency of Chrysodeixis includens (Lepidoptera: Noctuidae) field populations to Cry1Ac in Brazil.
abstract: BACKGROUND
  The soybean looper (SBL), Chrysodeixis includens (Walker), is one of the most important soybean pests in Brazil. MON 87701 × MON 89788 soybean expressing Cry1Ac has been recently deployed in Brazil, providing high levels of control against the primary lepidopteran pests. To support insect resistance management (IRM) programmes, the baseline susceptibility of SBL to Cry1Ac was assessed, and the resistance allele frequency was estimated on the basis of an F2 screen.
  
  
  RESULTS
  The toxicity (LC50 ) of Cry1Ac ranged from 0.39 to 2.01 µg mL(-1) diet among all SBL field populations collected from crop seasons 2008/09 to 2012/13, which indicated approximately fivefold variation. Cry1Ac diagnostic concentrations of 5.6 and 18 µg mL(-1) diet were established for monitoring purposes, and no shift in mortality was observed. A total of 626 F2 family lines derived from SBL collected from locations across Brazil during crop season 2014/15 were screened for the presence of Cry1Ac resistance alleles. None of the 626 families survived on MON 87701 × MON 89788 soybean leaf tissue (joint frequency 0.0004).
  
  
  CONCLUSIONS
  SBL showed high susceptibility and low resistance allele frequency to Cry1Ac across the main soybean-producing regions in Brazil. These findings meet important criteria for effective IRM strategy. © 2015 Society of Chemical Industry.
authors.affiliation: Universidade Federal do Paraná, Paraná, Brazil.
authors.forename: Silvia Ac
authors.initials: SA
authors.lastname: Yano
authors.affiliation: Embrapa Cerrados, Brasília, Brazil.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Specht
authors.affiliation: In memoriam.
authors.forename: Flávio
authors.initials: F
authors.lastname: Moscardi
authors.affiliation: Monsanto do Brasil Ltda, Sao Paulo, Brazil.
authors.forename: Renato A
authors.initials: RA
authors.lastname: Carvalho
authors.affiliation: Monsanto do Brasil Ltda, Sao Paulo, Brazil.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Dourado
authors.affiliation: Monsanto Company, St Louis, MO, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Martinelli
authors.affiliation: Monsanto Company, St Louis, MO, USA.
authors.forename: Graham P
authors.initials: GP
authors.lastname: Head
authors.affiliation: Embrapa Soybean, Londrina, Paraná, Brazil.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Sosa-Gómez
mesh_terms: D000818:Animals; D001938:Brazil; D004731:Endotoxins / Q000235:genetics*; D005787:Gene Frequency; D006460:Hemolysin Proteins / Q000235:genetics*; D007814:Larva / Q000502:physiology; D009036:Moths / Q000502:physiology*; D010572:Pest Control, Biological; D018515:Plant Leaves / Q000235:genetics; D030821:Plants, Genetically Modified; D013025:Glycine max / Q000235:genetics*
chemical_list: D004731:Endotoxins; D006460:Hemolysin Proteins
keywords: Cry1Ac; baseline susceptibility; resistance allele frequency; soybean looper