title: Stability and fitness costs associated with etoxazole resistance in Tetranychus urticae (Acari: Tetranychidae).
abstract: The two-spotted spider mite, Tetranychus urticae Koch, is one of the most important pests on a wide range of crops worldwide. Studies on stability of resistance and possible fitness costs associated with etoxazole resistance were carried out in T. urticae to provide basic information necessary to define effective acaricide resistance management strategies for this pest. Selection for resistance to etoxazole was performed in a population of T. urticae collected from a commercial rose field, in Holambra County, in the State of São Paulo, Brazil. After five rounds of selection for resistance, the resistance ratio (R/S) at the LC50 reached 8739 fold value in comparison with a susceptible strain (Brazabrantes S Strain). The stability of etoxazole resistance was studied under laboratory conditions, using a population with initial frequency of 75 % of resistant mites. The frequencies of etoxazole resistance were evaluated monthly for a period of 13 months. The frequency of etoxazole resistance decreased from 75 to 37 % in this period. Comparison of biological traits between resistant and susceptible strains indicated the presence of fitness costs associated with etoxazole resistance. The resistant strain showed lower fecundity and a higher proportion of males in the population. The figures for net reproductive rate (R 0), intrinsic rate of natural increase (r m) and finite rate of increase (λ) were higher in the susceptible strain. The instability of etoxazole resistance is a favorable aspect for the acaricide resistance management in the spider mite.
authors.affiliation: Instituto Biológico, APTA, Caixa Postal 70, Campinas City, São Paulo, CEP 13001-970, Brazil.
authors.forename: Rafael Sorrentino Minazzi
authors.initials: RS
authors.lastname: Stocco
authors.affiliation: Instituto Biológico, APTA, Caixa Postal 70, Campinas City, São Paulo, CEP 13001-970, Brazil. mesato@biologico.sp.gov.br.
authors.forename: Mário Eidi
authors.initials: ME
authors.lastname: Sato
authors.affiliation: Instituto Biológico, APTA, Caixa Postal 70, Campinas City, São Paulo, CEP 13001-970, Brazil.
authors.forename: Taiana Lumi
authors.initials: TL
authors.lastname: Santos
mesh_terms: D056810:Acaricides / Q000494:pharmacology; D000818:Animals; D001938:Brazil; D004351:Drug Resistance / Q000502:physiology*; D005260:Female; D056084:Genetic Fitness; D007814:Larva / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D008297:Male; D009758:Nymph / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D010080:Oxazoles / Q000494:pharmacology*; D012098:Reproduction / Q000187:drug effects; D040102:Tetranychidae / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000502:physiology
chemical_list: D056810:Acaricides; D010080:Oxazoles; C508136:etoxazole
keywords: Instability of resistance; Reproductive rate; Sex ratio; Two-spotted spider mite