Repellency and Laboratory Performance of Selected Insecticides to Field-Collected Insecticide Resistant German Cockroaches (Blattodea: Ectobiidae)

German cockroaches, Blattella germanica (L.) (Blattodea: Ectobiidae), are important indoor insect pests and remain difficult to control because of their ability to develop resistance to insecticides. The toxicity, resistance levels, repellency, and performance index (PI) value of five formulated insecticides (permethrin, chlorpyrifos, propoxur, imidacloprid, and fipronil) were determined for adult males of seven strains of the German cockroach: a laboratory-reared susceptible strain (S) and six field-collected strains (B, D, E, G, H, and I). Propoxur was generally the most toxic insecticide to all strains using continuous exposure methods; however, using Ebeling choice box methods, chlorpyrifos, and fipronil were most toxic. In both continuous exposure and Ebeling choice box tests, the field-collected strains were generally most resistant to permethrin among the five insecticides. The greatest increase in resistance ratios between the two exposure methods was for permethrin and propoxur. Permethrin was the most repellent insecticide against all but two strains (D and H). PI values reached 100 (no repellency and complete mortality) for the susceptible strain against only chlorpyrifos and fipronil. Only fipronil resulted in a PI value of 100 for any of the field-collected strains. Continuous exposure and Ebeling choice box resistance ratios were correlated, and both were correlated with previously reported resistance ratios (based on LD50 values). Choice box repellency, however, was only correlated with LD50 resistance ratios. PIMax was negatively correlated with all measures of resistance ratios.