title: Developmental penalties associated with inducible tolerance in Helicoverpa armigera to insecticidal toxins from Bacillus thuringiensis.
abstract: Exposure of insect larvae to sublethal concentrations of crystal toxins from the soil bacterium Bacillus thuringiensis (Bt toxins) causes the induction of immune and metabolic responses that can be transmitted to offspring by epigenetic inheritance mechanisms. Given that the elevated immune status carries significant developmental penalties, we wanted to establish the relationships between immune induction, tolerance to the toxin and developmental penalties. A laboratory culture of Helicoverpa armigera was induced by a sublethal bacterial suspension containing crystal toxin Cry1Ac in one generation and maintained in the presence of toxin, acquiring significant levels of tolerance to the toxin within 12 generations of continuous exposure. Comparing tolerant and susceptible insects, we show that the induction of larval immune response and the coincident alteration of development-related metabolic activities by elicitors in the larval gut (larval induction) differs from the elevated immune status transmitted by epigenetic mechanisms (embryonic induction). Because the damaging effects of larval induction processes are higher compared to embryonic induction, it is likely that overall developmental penalties depend on the relative contribution of the two induction processes. When insects are kept with the same amount of toxin in the diet for subsequent generations, the embryonic induction process increases its contribution compared to the larval induction, resulting in reduced overall developmental penalty, while tolerance to the toxin is maintained.
authors.affiliation: Insect Molecular Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia.
authors.forename: Mahbub
authors.initials: M
authors.lastname: Rahman
authors.forename: Richard
authors.initials: R
authors.lastname: Glatz
authors.forename: Rick
authors.initials: R
authors.lastname: Roush
authors.forename: Otto
authors.initials: O
authors.lastname: Schmidt
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000633:toxicity; D001835:Body Weight / Q000187:drug effects; D004361:Drug Tolerance; D004627:Embryonic Induction; D004731:Endotoxins; D044127:Epigenesis, Genetic; D006460:Hemolysin Proteins; D007305:Insecticide Resistance; D007814:Larva / Q000187:drug effects / Q000276:immunology; D009036:Moths / Q000187:drug effects / Q000196:embryology / Q000254:growth & development / Q000276:immunology
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis