title: Fitness of Bt-resistant cabbage loopers on Bt cotton plants.
abstract: Development of resistance to the insecticidal toxins from Bacillus thuringiensis (Bt) in insects is the major threat to the continued success of transgenic Bt crops in agriculture. The fitness of Bt-resistant insects on Bt and non-Bt plants is a key parameter that determines the development of Bt resistance in insect populations. In this study, a comprehensive analysis of the fitness of Bt-resistant Trichoplusia ni strains on Bt cotton leaves was conducted. The Bt-resistant T. ni strains carried two genetically independent mechanisms of resistance to Bt toxins Cry1Ac and Cry2Ab. The effects of the two resistance mechanisms, individually and in combination, on the fitness of the T. ni strains on conventional non-Bt cotton and on transgenic Bt cotton leaves expressing a single-toxin Cry1Ac (Bollgard I) or two Bt toxins Cry1Ac and Cry2Ab (Bollgard II) were examined. The presence of Bt toxins in plants reduced the fitness of resistant insects, indicated by decreased net reproductive rate (R0) and intrinsic rate of increase (r). The reduction in fitness in resistant T. ni on Bollgard II leaves was greater than that on Bollgard I leaves. A 12.4-day asynchrony of adult emergence between the susceptible T. ni grown on non-Bt cotton leaves and the dual-toxin-resistant T. ni on Bollgard II leaves was observed. Therefore, multitoxin Bt plants not only reduce the probability for T. ni to develop resistance but also strongly reduce the fitness of resistant insects feeding on the plants.
authors.affiliation: Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, USA.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tetreau
authors.affiliation: Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, USA.|Department of Entomology, Nanjing Agricultural University, Nanjing, China.
authors.forename: Ran
authors.initials: R
authors.lastname: Wang
authors.affiliation: Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D005260:Female; D056084:Genetic Fitness; D003368:Gossypium; D006460:Hemolysin Proteins; D060434:Herbivory; D007305:Insecticide Resistance; D008297:Male; D009036:Moths / Q000502:physiology*; D010058:Oviposition; D030821:Plants, Genetically Modified; D011158:Population Growth
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: 
  Bacillus thuringiensis
  ; 
  Trichoplusia ni
  ; Cry1Ac; Cry2Ab; fitness cost of resistance; genetically modified cotton