Report 
  Title  
  PYRETHROID RESISTANCE MECHANISMS IN THE GERMAN COCKROACH (DICTYOPTERA: BLATTELLIDAE)
  Key Words  
  Blattella germanica, resistance profiles, tarsal-contact method, synergists
  Author  
  DONALD G. COCHRAN
  Abstract  
  Resistance to pyrethroid insecticides has become common in field populations of the German cockroach, Blattella germanica (L.), in the United States and elsewhere. Some populations are highly resistant to as many as eight or nine pyrethroids. The primary mechanisms of resistance are enzymatic degradation of the insecticide and target-site insensitivity. Tests, using the tarsal-contact method, formed the basis for a further analysis. Resistance to pyrethrins is specific, and can be completely negated by piperonyl butoxide (PBO). Resistance to allethrin is also specific, but PBO has no effect on it. Resistance to several of the more advanced pyrethroids developed later and initially could be negated by PBO. Subsequently and progressively, PBO had little or no effect on resistance to these compounds. Analysis of resistance profiles for a large number of field populations indicates that the PBO-sensitive resistance to permethrin, phenothrin, fenvalerate, and cypermethrin developed independently. Similarly, the PBO-insensitive resistance to these compounds also developed in a stepwise manner. While data of this type do not establish the details of each mechanism, they clearly indicate the existence of numerous pyrethroid-resistance mechanisms in the German cockroach.