Chlorpyrifos resistance in German cockroaches (Dictyoptera: Blatellidae) from restaurants.

Visual inspections and trapping revealed the presence of German cockroaches, Blattella germanica (L.) in 62 of 100 randomly selected commercial food-handling establishments. From live cockroaches trapped in 55 restaurants, 35 strains were established and tested for chlorpyrifos resistance. Poor sanitation and the likelihood of trapping cockroaches were associated. Twenty strains had resistance ratios (RR) as LD50 greater than 10-fold, a value exceeding the pest management threshold level for this insecticide. Resistance ratios were not associated with numbers of cockroaches trapped, the level of sanitation, numbers of different insecticide products used, or the number of treatments per month. Significantly more categories of insecticides (e.g., carbamate, organophosphate, inorganic) were used in restaurants with RR greater than 10 than in those with RR less than 10.