Resistance to Pyrethrins in the German Cockroach: Inheritance and Gene-Frequency Estimates in Field-Collected Populations (Dictyoptera: Blattellidae)

Pyrethrins resistance was assessed genetically in the German cockroach, Blattella germanica (L.), by conventional crossing experiments. It is inherited as a simple, autosomal, incompletely dominant, trait. By manipulating the test procedure, the susceptible homozygote was clearly identified, allowing gene frequency estimates to be made using the Hardy-Weinburg equilibrium expression. Gene frequencies were estimated for four susceptible and 16 resistant field-collected populations. Values ranged from 0.10 to 0.18 for the susceptible strains, and from 0.34 to > 0.90 for the resistant strains. Changes in gene frequency over time for several resistant strains were not significant. The results are discussed from the standpoints of their effects on cockroach control and the stability of pyrethrins resistance even during extended periods with no selection pressure.