title: The in vitro response of field strains of sheep blowflies Lucilia sericata and L. cuprina (Calliphoridae) in New Zealand to dicyclanil and triflumuron.
abstract: OBJECTIVE
  To evaluate the in vitro efficacy of triflumuron and dicyclanil against field strains of Lucilia sericata and L. cuprina in New Zealand to establish whether anecdotal reports of declining protection periods afforded by dips containing these active ingredients had validity.
  
  
  METHODS
  Strains of field-derived blowflies (Lucilia cuprina and L. sericata) were obtained from adult flies from flytraps or larvae from sheep with flystrike submitted from seven regions of the North and two regions of the South Islands of New Zealand. A total of 27 strains of L. sericata and 19 of L. cuprina were established in culture and first instar larvae obtained were exposed in vitro to dilution series of technical-grade dicyclanil (a pyrimidine carbonitrile) and triflumuron (a benzoyl urea). Concentrations lethal to 50% (LC50) and 95% (LC95) of each strain were calculated and tested by probit analysis, with the ratio of LC50 of each strain divided by LC50 of the most susceptible strain (resistance factor) derived in order to facilitate between-strain comparisons of susceptibility.
  
  
  RESULTS
  There was considerable variation between strains of L. sericata larvae in their susceptibility to triflumuron, with those least susceptible originating from the Waikato region. Strains from both Tararua and Manawatu regions were most susceptible and East Coast strains intermediate. All strains of the species tested showed a narrow band of susceptibility to dicyclanil with no regional trends apparent.
  
  
  CONCLUSIONS
  Representative field-strains of sheep blowflies exhibited a range of susceptibilities to both triflumuron and dicyclanil, suggestive of both genetic heterogeneity among fly populations and the spectrum of dip use in their source areas. This means there should be concerns for the long-term benefits of benzoyl urea insecticides for sheep farmers in New Zealand, but not yet for dicyclanil-based formulations.
  
  
  CONCLUSIONS
  Flystrike is a debilitating and occasionally lethal disease in sheep such that efficacious sheep dips have prophylactic value in reducing the prevalence of the condition.
authors: AgResearch Grasslands, Palmerston North, New Zealand. tania.waghorn@agresearch.co.nz
authors: T S
authors: TS
authors: Waghorn
authors: C H
authors: CH
authors: McKay
authors: A Cg
authors: AC
authors: Heath
mesh_terms: D000818:Animals; D001549:Benzamides / Q000494:pharmacology*; D004175:Diptera / Q000187:drug effects*; D007306:Insecticides / Q000494:pharmacology*; D007605:Juvenile Hormones / Q000494:pharmacology; D009520:New Zealand
chemical_list: D001549:Benzamides; D007306:Insecticides; D007605:Juvenile Hormones; C023957:triflumuron; C121718:dicyclanil