title: Cross-resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against the cotton bollworm.
abstract: To delay evolution of pest resistance to transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt), the "pyramid" strategy uses plants that produce two or more toxins that kill the same pest. We conducted laboratory diet experiments with the cotton bollworm, Helicoverpa armigera, to evaluate cross-resistance and interactions between two toxins in pyramided Bt cotton (Cry1Ac and Cry2Ab). Selection with Cry1Ac for 125 generations produced 1000-fold resistance to Cry1Ac and 6.8-fold cross-resistance to Cry2Ab. Selection with Cry2Ab for 29 generations caused 5.6-fold resistance to Cry2Ab and 61-fold cross-resistance to Cry1Ac. Without exposure to Bt toxins, resistance to both toxins decreased. For each of the four resistant strains examined, 67 to 100% of the combinations of Cry1Ac and Cry2Ab tested yielded higher than expected mortality, reflecting synergism between these two toxins. Results showing minor cross-resistance to Cry2Ab caused by selection with Cry1Ac and synergism between these two toxins against resistant insects suggest that plants producing both toxins could prolong the efficacy of Bt cotton against this pest in China. Including toxins against which no cross-resistance occurs and integrating Bt cotton with other control tactics could also increase the sustainability of management strategies.
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Jizhen
authors.initials: J
authors.lastname: Wei
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Yuyuan
authors.initials: Y
authors.lastname: Guo
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Gemei
authors.initials: G
authors.lastname: Liang
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Kongming
authors.initials: K
authors.lastname: Wu
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Tabashnik
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Xianchun
authors.initials: X
authors.lastname: Li
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000633:toxicity*; D004731:Endotoxins / Q000633:toxicity*; D003368:Gossypium / Q000469:parasitology*; D006460:Hemolysin Proteins / Q000633:toxicity*; D007305:Insecticide Resistance / Q000187:drug effects*; D009036:Moths / Q000187:drug effects* / Q000502:physiology
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis