title: Mechanisms of resistance to malathion in the medfly Ceratitis capitata.
abstract: Target site insensitivity and metabolic resistance mediated by esterases have been previously suggested to be involved in resistance to malathion in a field-derived strain (W) of Ceratitis capitata. In the present study, we have obtained the coding sequence for acetylcholinesterase (AChE) gene (Ccace) of C. capitata. An allele of Ccace carrying only a point mutation Gly328Ala (Torpedo numbering) adjacent to the glutamate of the catalytic triad was found in individuals of the W strain. Adult flies homozygotes for this mutant allele showed reduced AChE activity and less sensitivity to inhibition by malaoxon, showing that target site insensitivity is one of the factors of malathion resistance. In addition, all individuals from the resistant W strain showed reduced aliesterase activity, which has been associated with specific malathion resistance in higher Diptera. However, the alphaE7 gene (CcalphaE7), sequenced in susceptible and resistant individuals, did not carry any of the mutations associated with organophosphorus insecticide resistance in other Diptera. Another esterase mechanism, perhaps a carboxylesterase selective for malathion, in addition to mutant AChE, thus contributes to malathion resistance in C. capitata.
authors.affiliation: Dpto. de Biología de Plantas, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Magaña
authors.forename: Pedro
authors.initials: P
authors.lastname: Hernández-Crespo
authors.forename: Alexandra
authors.initials: A
authors.lastname: Brun-Barale
authors.forename: Francisco
authors.initials: F
authors.lastname: Couso-Ferrer
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Bride
authors.forename: Pedro
authors.initials: P
authors.lastname: Castañera
authors.forename: René
authors.initials: R
authors.lastname: Feyereisen
authors.forename: Félix
authors.initials: F
authors.lastname: Ortego
mesh_terms: D000110:Acetylcholinesterase / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D033622:Ceratitis capitata / Q000201:enzymology / Q000235:genetics*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D018076:DNA, Complementary; D019476:Insect Proteins / Q000235:genetics; D007305:Insecticide Resistance / Q000235:genetics; D007306:Insecticides; D007700:Kinetics; D008294:Malathion; D017354:Point Mutation; D017422:Sequence Analysis, DNA
chemical_list: D002800:Cholinesterase Inhibitors; D018076:DNA, Complementary; D019476:Insect Proteins; D007306:Insecticides; D000110:Acetylcholinesterase; D008294:Malathion