title: Dramatic developmental changes in larval knockdown response enhance genetic sexing based on DDT resistance in Anopheles stephensi (Diptera: Culicidae).
abstract: Genetic sexing systems based on a conditional lethal require good discrimination between the different phenotypes. DDT resistance in the early instars of Anopheles stephensi Liston is not a good candidate when based on mortality, but this study shows that the knockdown response gives exceptional discrimination between heterozygous resistant and homozygous susceptible individuals. One- and two-day-old larvae of the DlDDT strain showed high (417-fold) resistance to knockdown by DDT, but very low resistance to mortality (3.3-fold). This changes with the onset of the third instar, so that by the fourth instar, mortality resistance is high (108-fold) and knockdown resistance is low (6.5-fold). Susceptibility to DDT decreases from first to fourth instar in the susceptible strain by 443-fold for knockdown and 15-fold for mortality and in the resistant strain by 8.5-fold for knockdown and 491-fold for mortality. The DDT knockdown response in young larvae was successfully used to identify two Y-autosome translocations linked to the resistance gene, DDT. T(Y-3)69 and T(Y-3)72 gave recombination values between the translocation breakpoint and the DDT locus of 4.1 and 10.1 crossover units, respectively. T(Y-3)69 proved to be an adequate genetic sexing system for laboratory studies.
authors.affiliation: School of Biological Sciences, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK. c.a.malcolm@qmw.ac.uk
authors.forename: C A
authors.initials: CA
authors.lastname: Malcolm
authors.forename: A S
authors.initials: AS
authors.lastname: Robinson
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D003634:DDT / Q000494:pharmacology*; D005260:Female; D007305:Insecticide Resistance / Q000235:genetics; D007814:Larva / Q000254:growth & development; D008297:Male
chemical_list: D003634:DDT