Report 
  Title  
  PREVALENCE AND MAGNITUDE OF RESISTANCE TO CYCLODIENE AND PHENYLPYRAZOLE INSECTICIDES IN BLATTELLA GERMANICA AND DROSOPHILA MELANOGASTER
  Key Words  
  Cockroach, fipronil, cross-resistance, chlordane, GABA receptor.
  Author  
  J. R. BLOOMQUIST AND Wm. H ROBINSON
  Abstract  
  The utility of fipronil and perhaps other phenylpyrazoles for German cockroach, Blattella germanica, control may be affected by resistance to cyclodienes in field populations, because of cross resistance between these two classes of insecticides. Field populations of B. germanica were sampled for the presence of chlordane resistance, and to determine whether chlordane resistance confers cross-resistance to fipronil in these populations. Additional screening experiments with fipronil and JKU 0422 were also performed on cockroaches, and a strain of Drosophila melanogaster (Meigen) that shows high levels of cyclodiene resistance. Six field strains of German cockroach were collected from household populations in Virginia, USA. Physiological resistance was detected in all the strains; resistance ratios ranged from RR = 3 to RR = 33. The data indicate the potential for the presence and variability of chlordane resistance in the field. However, there was no indication of cross-resistance to the phenylpyrazoles fipronil or JKU 0422 in field strains. The strain of D. melanogaster showed 35fold resistance to fipronil. Relatively low resistance to fipronil and high resistance to JKU 0422 was observed in cyclodiene-resistant laboratory strains of B. germanica and D. melanogaster. The structural dependence of this large difference apparently resides in the chemical substituents at the 3 and 5 position on the pyrazole ring. Cyclodiene resistance is primarily due to a specific mutation of Ala to Ser at position 302 in a GABA receptor subunit gene, and this mutation has been found in a number of cyclodiene-resistant insect species. Additional polymorphisms are found in cyclodiene-resistant strains of B. germanica. We hypothesize that two mechanisms of resistance are present, with the mechanism providing the highest level of resistance being an altered GABA