Multiple and Cross-Resistance in a Field-Collected Strain of the German Cockroach (Orthoptera: Blattellidae)1

A field-collected strain of Blattella germanica (L.) was highly resistant (LT5 resistance ratio < 90X) to bendiocarb. The strain, which was collected from public housing in Baltimore, Md., was found also to be resistant to chlordane (8.2 ×), diazinon (3.7 ×), malathion (6.5 ×), and propoxur (13.3 ×). Chlorpyrifos was still effective against this strain of German cockroach in both public housing and laboratory assays. Since the area where the parent stock was collected had been previously treated only once with bendiocarb, this is another example of cross-resistance. The laboratory-determined resistance level likely accounts for the control failures when bendiocarb was used in Baltimore Housing and Community Development units.