Article INCREASE IN LARVAL GUT PROTEOLYTIC ACTIVITIES AND Bti RESISTANCE IN THE DENGUE FEVER MOSQUITO Guillaume Tetreau, Renaud Stalinski, Jean-Philippe David, and Laurence Despr ´ es Laboratoire d’Ecologie Alpine, LECA-UMR 5553, Universit´ e de Grenoble 1, Grenoble cedex, France The bioinsecticide Bacillus thuringiensis var. israelensis (Bti) is increasingly used worldwide for mosquito control. Although no established resistance to Bti has been described in the field so far, a resistant Aedes aegypti strain (LiTOX strain) was selected in the laboratory using field-collected leaf litter containing Bti toxins. This selected strain exhibits a moderate resistance level to Bti, but a high resistance level to individual Cry toxins. As Bti contains four different toxins, generalist resistance mechanisms affecting mosquito tolerance to different toxins were expected in the resistant strain. In the present work, we show that the resistant strain exhibits an increase of various gut proteolytic activities including trypsins, leucine-aminopeptidases, and carboxypeptidase A activities. These elevated proteolytic activities resulted in a faster activation of Cry4Aa protoxins while Cry4Ba or Cry11Aa were not affected. These results suggest that changes in proteolytic activities may contribute to Bti resistance in mosquitoes together with other mechanisms. C  2012 Wiley Periodicals, Inc. Keywords: B. thuringiensis israelensis; mosquito; gut extracts; proteolytic activities; resistance Supporting Information is available in the online issue at wileyonlinelibrary.com. Grant sponsor: French National Research Agency and French Rhˆ one-Alpes region. The authors declare that no conflict of interest exists. Guillaume Tetreau and Renaud Stalinski contributed equally to this work. Correspondence to: Guillaume Tetreau, Laboratoire d’Ecologie Alpine—Universit´ e de Grenoble 1, 2233 rue de la Piscine, 8400 Saint-Martin d’H` eres, France. E-mail: guillaume.tetreau@gmail.com ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY, Vol. 82, No. 2, 71–83 (2013) Published online in Wiley Online Library (wileyonlinelibrary.com). C  2012 Wiley Periodicals, Inc. DOI: 10.1002/arch.21076