Absence of a fitness penalty in insecticide-resistant German cockroaches,Blattella germanica(L.) (Dictyoptera: Blattellidae)

We investigated life-history variables of insecticide-resistant and insecticide-susceptible German cockroaches, Blattella germanica (L.) with a view to finding evidence of reduced fitness in the resistant strains compared to the susceptible ones. Most resistant strains showed no significant difference in nymphal development period, preoviposition period, incubation period, nymphal and oothecal production, ootheca dimensions, nymphal survivorship, and adult longevity compared to those of the susceptible strain. However, in resistant strains each instar stage was shorter compared to the equivalent instar of the susceptible strain. These results indicate that resistance is not a costly trait in the German cockroach, contrary to expectations.