title: Influence of Ephestia kuehniella stage larvae on the potency of Bacillus thuringiensis Cry1Aa delta-endotoxin.
abstract: The economically important crop pest Ephestia kuehniella was tested at two stages of larval development for susceptibility to Bacillus thuringiensis Cry1Aa toxin. Bioassays showed that toxicity decreased during the development of larvae stage. In fact, Cry1Aa toxins from BNS3-Cry-(pHT-cry1Aa) showed low toxicity against the first-instar larvae (L1) with a LC50value of about 421.02μg/g of diet and was not toxic against the fifth-instar (L5), comparing to the BLB1 toxins used as positive control which represent a LC50value of about 56.96 and 84.21μg/g of diet against L1 and L5 instars larvae, respectively. Effects of Cry1Aa toxins were reflected in histopathological observations by the weak destruction of midgut epithelium, slight hypertrophy of epithelial cells, and minor alteration of brush border membrane (BBM) detected mainly in L1 larvae stage comparing to the more extensive damage caused by BLB1 toxins. Interestingly, in vitro proteolysis of Cry1Aa toxins was found to correlate with the difference of toxicity during larval stage development. In fact, the weak proteinase activity detected inside the L1 midgut has led to the persistence of the Cry1Aa active forms (65 and 58kDa) during prolonged incubations, causing the alterations described previously. Three subfamilies of aminopeptidase (APN) receptors were detected in both larvae instars with different intensities and molecular weights (150kDa and 55kDa for APN1, and 90kDa for APN2 and APN4). Remarkably, binding assay using Cry1Aa toxin seems to have no direct correlation with larval stages toxicity differences, since same putative receptors were detected. Understanding the reasons for the clear differences in the effectiveness of Cry1Aa toxins during larval development stages of E. kuehniella is very important for the design of future improvement insecticidal approaches and for the accomplishment of resistance prevention strategies.
authors.affiliation: Laboratory of Biopesticides, Centre of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
authors.forename: Nouha
authors.initials: N
authors.lastname: Abdelmalek
authors.affiliation: Laboratory of Biopesticides, Centre of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
authors.forename: Sameh
authors.initials: S
authors.lastname: Sellami
authors.affiliation: Faculty of Sciences, University Saint-Joseph, Beirut, Lebanon.
authors.forename: Mireille
authors.initials: M
authors.lastname: Kallassy-Awad
authors.affiliation: Laboratory of Molecular and Cellular Screening Processes Genomics and Bioinformatics, Centre of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
authors.forename: Molka Feki
authors.initials: MF
authors.lastname: Tounsi
authors.affiliation: University of Ferhat ABBAS Sétif 1, Algeria.
authors.forename: Abdelkrim
authors.initials: A
authors.lastname: Mebarkia
authors.affiliation: Laboratory of Biopesticides, Centre of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
authors.forename: Slim
authors.initials: S
authors.lastname: Tounsi
authors.affiliation: Laboratory of Biopesticides, Centre of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia. Electronic address: souad.rouis@cbs.rnrt.tn.
authors.forename: Souad
authors.initials: S
authors.lastname: Rouis
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000254:growth & development* / Q000378:metabolism; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000633:toxicity*; D004731:Endotoxins / Q000633:toxicity*; D006460:Hemolysin Proteins / Q000633:toxicity*; D007814:Larva; D009036:Moths / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology; D010572:Pest Control, Biological
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: APN; Bacillus thuringiensis; Binding experiments; Cry1Aa; Ephestia kuehniella; Proteinases content