title: Fate of Bacillus thuringiensis subsp. israelensis in the field: evidence for spore recycling and differential persistence of toxins in leaf litter.
abstract: Bacillus thuringiensis subsp. israelensis is a bioinsecticide increasingly used worldwide for mosquito control. Despite its apparent low level of persistence in the field due to the rapid loss of its insecticidal activity, an increasing number of studies suggested that the recycling of B. thuringiensis subsp. israelensis can occur under specific, unknown conditions. Decaying leaf litters sampled in mosquito breeding sites in the French Rhône-Alpes region several months after a treatment were shown to exhibit a high level of larval toxicity and contained large amounts of spores. In the present article, we show that the high concentration of toxins found in these litters is consistent with spore recycling in the field, which gave rise to the production of new crystal toxins. Furthermore, in these toxic leaf litter samples, Cry4Aa and Cry4Ba toxins became the major toxins instead of Cyt1Aa in the commercial mixture. In a microcosm experiment performed in the laboratory, we also demonstrated that the toxins, when added in their crystal form to nontoxic leaf litter, exhibited patterns of differential persistence consistent with the proportions of toxins observed in the field-collected toxic leaf litter samples (Cry4 > Cry11 > Cyt). These results give strong evidence that B. thuringiensis subsp. israelensis recycled in specific breeding sites containing leaf litters, and one would be justified in asking whether mosquitoes can become resistant when exposed to field-persistent B. thuringiensis subsp. israelensis for several generations.
authors.affiliation: Laboratoire d'Ecologie Alpine, LECA-UMR 5553, Université de Grenoble 1, Grenoble, France. guillaume.tetreau@gmail.com
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tetreau
authors.forename: Mattia
authors.initials: M
authors.lastname: Alessi
authors.forename: Sylvie
authors.initials: S
authors.lastname: Veyrenc
authors.forename: Sophie
authors.initials: S
authors.lastname: Périgon
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: David
authors.forename: Stéphane
authors.initials: S
authors.lastname: Reynaud
authors.forename: Laurence
authors.initials: L
authors.lastname: Després
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000254:growth & development* / Q000472:pathogenicity; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000032:analysis / Q000633:toxicity; D009033:Culicidae / Q000382:microbiology / Q000502:physiology; D004731:Endotoxins / Q000032:analysis / Q000633:toxicity; D004783:Environmental Microbiology; D005602:France; D006460:Hemolysin Proteins / Q000032:analysis / Q000633:toxicity; D007814:Larva / Q000382:microbiology / Q000502:physiology; D013171:Spores, Bacterial / Q000254:growth & development* / Q000472:pathogenicity; D016019:Survival Analysis
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis