title: Fitness costs of reproductive capacity and ovarian development in a Bt-resistant strain of the cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).
abstract: BACKGROUND
  The cotton bollworm Helicoverpa armigera has developed resistance to the insecticidal Cry1Ac toxins produced by Bacillus thuringiensis (Bt) in China. To gain a better understanding of the fitness cost associated with resistance evolution, reproductive capacities and ovarian development were examined in four strains of H. armigera: a Cry1Ac-susceptible strain (96S); a Cry1Ac-resistant strain fed on an artificial diet with Cry1Ac toxin for 135 generations (BtR); two strains derived from BtR: a strain grown without Cry1Ac selection for 38 generations (CK1) and a strain grown for one generation without Cry1Ac selection (CK2).
  
  
  RESULTS
  Strains 96S and CK1 had similar reproductive capacity and Cry1Ac susceptibility. Compared with the 96S and CK1 strains, the fecundity and hatching rate of CK2 were respectively more than 30% and 50% lower. Moreover, the number of eggs laid by BtR was significantly lower than the number of eggs laid by 96S and CK1, but higher than the number of eggs laid by CK2. In accordance with the differences in reproductive capacity, ovarian development in CK2 and BtR was significantly delayed.
  
  
  CONCLUSIONS
  These results indicated that there was a fitness cost in the reproductive physiology in the resistant strains. Reversion to susceptibility to the Bt Cry-toxin in the resistant CK1 strain was associated with an increase in reproductive capacity.
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Wanna
authors.initials: W
authors.lastname: Zhang
authors.forename: Long
authors.initials: L
authors.lastname: Ma
authors.forename: Feng
authors.initials: F
authors.lastname: Zhong
authors.forename: Yanan
authors.initials: Y
authors.lastname: Wang
authors.forename: Yuyuan
authors.initials: Y
authors.lastname: Guo
authors.forename: Yanhui
authors.initials: Y
authors.lastname: Lu
authors.forename: Gemei
authors.initials: G
authors.lastname: Liang
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000378:metabolism; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000378:metabolism*; D004731:Endotoxins / Q000378:metabolism*; D005260:Female; D056084:Genetic Fitness; D006460:Hemolysin Proteins / Q000378:metabolism*; D009036:Moths / Q000235:genetics / Q000502:physiology*; D010053:Ovary / Q000502:physiology; D010572:Pest Control, Biological; D012098:Reproduction; D013045:Species Specificity
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: Bacillus thuringiensis (Bt); Helicoverpa armigera; fitness cost; reproductive physiology; resistance