INSECTICIDE RESISTANCE IN BLATTELLA GERMANICA (L.) (DICTYOPTERA: BLATTELLIDAE) FROM FOOD PRODUCING ESTABLISHMENTS IN DENMARK

Abstract:
Laboratory from 1987 to 1991. A screening of the insecticide resistance in B. germanica in some selected locations was conducted with permethrin using tarsal contact tests to estimate KT50, (/WHO/VBC/75.593). Based on these data more detailed measurement of the resistance in the German Cockroaches from chosen locations was then assessed by topical application techniques; 2.5 p1 insecticide in acetone on the ventral sclerites of the cockroaches was used. Permethrin. deltamethrin, diazinon, and chlorpyrifos were used in these trials. Probit analysis was used with both methods, according to Finney (1971) and similar results obtained with the DPIL susceptible strain were used to calculate the resistance/ susceptibility ratio (R/S). The cockroaches were mainly collected from mass food producing kitchens, bakeries, and a zoological garden in Copenhagen and North Zealand, but some were also collected in food producing factories in Aarhus, Jutland, and from residential buildings in Nuuk, Greenland. In the topical application tests, female cockroaches from ten different locations were tested for their susceptibility to permethrin. The calculated R/S ratio based on the LC50's varied between 1 and 57. For deltamethrin from eight locations, the R/S ratio varied between 2 and 31, for chlorpyrifos from nine locations, the R/S ratio varied between 1 and 4, and for diazinon from six locations, the R/S ratio varied between 1 and 2. Based on these findings, the reason for control failure in these particular locations could be ascribed to resistance to the two pyrethroids, permethrin and deltamethrin. Both insecticides were in use for cockroach control in Denmark at that time. The organophosphate, chlorpyrifos, with its low R/S ratio was then used in the locations, and with good results.