title: Movement and survival of Busseola fusca (Lepidoptera: Noctuidae) larvae within maize plantings with different ratios of non-Bt and Bt seed.
abstract: BACKGROUND
  Products of plant biotechnology, for example genetically modified Bt maize, provide useful tools for pest management. The benefits provided by insect-resistant plants are, however, threatened by the evolution of resistance by target pest species. The high-dose/refuge insect resistance management strategy (IRM) as well as seed mixtures are globally used as IRM strategies. Busseola fusca (Lepidoptera: Noctuidae), the target stem borer of Bt maize in Africa, evolved resistance to Bt maize expressing Cry1Ab protein in South Africa. Owing to high larval mobility and subsequent sublethal exposure of larvae moving between non-Bt and Bt plants, more rapid resistance evolution has been proposed as a possibility with deployment of seed mixture strategies.
  
  
  RESULTS
  Laboratory and field studies were conducted to study B. fusca larval mobility. In the laboratory, different scenarios of B. fusca larval movement between single-gene (Cry1Ab) and stacked-trait (Cry1A.105 and Cry2Ab2) Bt maize were studied. Data on larval survival and mass over time indicated that Cry proteins do not kill larvae above certain developmental stages. A 2 year field study with the single gene and the stacked event was conducted using seed mixtures containing 5, 10, 15 and 20% non-Bt seed as well as a control treatment (non-Bt seed only).
  
  
  CONCLUSIONS
  Larval movement continued for 5 weeks and resulted in a significant incidence of Bt and non-Bt damaged plants, indicating that the movement behaviour of B. fusca is of such a nature that seed mixtures as an IRM strategy may not be effective to delay resistance evolution. © 2016 Society of Chemical Industry.
authors.affiliation: ARC - Grain Crops Institute, Potchefstroom, South Africa. erasmusa@arc.agric.za.
authors.forename: Annemie
authors.initials: A
authors.lastname: Erasmus
authors.affiliation: Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa.
authors.forename: Jaco
authors.initials: J
authors.lastname: Marais
authors.affiliation: Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa.
authors.forename: Johnnie
authors.initials: J
authors.lastname: Van den Berg
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics*; D004731:Endotoxins / Q000235:genetics*; D006460:Hemolysin Proteins / Q000235:genetics*; D007305:Insecticide Resistance / Q000502:physiology; D007814:Larva / Q000254:growth & development; D009036:Moths / Q000502:physiology*; D030821:Plants, Genetically Modified; D012639:Seeds / Q000235:genetics; D013019:South Africa; D016019:Survival Analysis; D003313:Zea mays / Q000235:genetics* / Q000502:physiology
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: Cry proteins; genetically modified crops; larval movement; refuge; resistance evolution; stem borers