title: Decline of pyrethroid resistance in the absence of selection pressure in a population of German cockroaches (Dictyoptera: Blattellidae).
abstract: The level of resistance to seven pyrethroids was followed in a laboratory-selected population of Blattella germanica (L.) for 15 generations, during which time it was not exposed to any insecticide. As estimated by LT50 resistance ratios (RRs), resistance declined in a stepwise manner to preselection levels with all of the pyrethroids except pyrethrins. I also compared the levels of resistance as indicated by RRs and by gene frequency (GF) estimates. Results showed that GF estimates provide a more precise indication of the changes in resistance that occur over time than do RRs alone, especially when combined with RR and end-point mortality data. I discuss my results from the standpoints of the number of genetic mechanisms involved in pyrethroid resistance in this insect, and what the declines in resistance mean for future cockroach control.
authors.affiliation: Department of Entomology, Virginia Polytechnic Institute & State University, Blacksburg 24061-0319.
authors.forename: D G
authors.initials: DG
authors.lastname: Cochran
mesh_terms: D000818:Animals; D003058:Cockroaches / Q000235:genetics*; D005787:Gene Frequency; D007305:Insecticide Resistance / Q000235:genetics; D011722:Pyrethrins / Q000494:pharmacology*; D012641:Selection, Genetic
chemical_list: D011722:Pyrethrins