title: Plant-toxin interactions in transgenic Bt cotton and their effect on mortality of Helicoverpa armigera (Lepidoptera: Noctuidae).
abstract: In Australia, transgenic cotton plants expressing the cry1Ac gene from Bacillus thuringiensis Berliner variety kurstaki are less toxic to first-instar Helicoverpa armigera (Hübner) after the plant is producing fruit. We developed two bioassay methods (leaf mush, leaf disk) to test if the physiological state of the plants explained changes in toxicity and a third method (diet incorporation) was developed to quantify the toxicity of Bt leaves when mixed in chickpea diet. Cry1Ac protein was less toxic to H. armigera larvae when the protein was mixed with leaves from fruiting versus presquare conventional cotton. Differences in LC50 varied from 2.4- to 726-fold, depending on the source of toxin and conventional plant material. These results suggest that plant-toxin interactions in fruiting cotton are reducing the toxicity of the Cry1Ac protein. The possible role of tannins in these changes is discussed.
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Entomology and Australian Cotton CRC, Canberra, ACT, Australia.
authors.forename: K M
authors.initials: KM
authors.lastname: Olsen
authors.forename: J C
authors.initials: JC
authors.lastname: Daly
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D001681:Biological Assay; D004731:Endotoxins / Q000235:genetics; D003368:Gossypium; D006460:Hemolysin Proteins; D007306:Insecticides; D009036:Moths; D010572:Pest Control, Biological / Q000379:methods; D030821:Plants, Genetically Modified; D014867:Water
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D014867:Water