Toxicity of Two Carbamate Insecticides to Resistant and Normal Strains of the German Cockroach1

A tarsal contact method was employed to test the toxicity of the carbamate materials Baygon® (o-isopropoxyphenyl methyl carbamate) and MCA-600 (benzo[b]thien-4-yl methyl carbamate) to 3 strains of the German cockroach, Blaltella germanica (L.), resistant to certain organophosphate insecticides. Comparison of dosage mortality data with similar data for a normal strain indicated a slight loss of susceptibility to both materials in a laboratory strain selected for resistance to diazinon. A field strain from Dallas, Texas, having low-level resistance to malathion, fenthion, and diazinon, showed no significant resistance to either Baygon or MCA-600, whereas a laboratory strain, resistant to malathion, was more susceptible to the carbamates than the normal strain. Results show that Baygon was more toxic than MCA-600 to adult German cockroaches of all strains.