MEASURING CYPERMETHRIN RESISTANCE IN THE GERMAN-COCKROACH (ORTHOPTERA, BLATTELLIDAE)

Cypermethrin resistance in the German cockroach, Blattella germanica ( L.), was assessed by tests of surface contact and topical application. Topical application provided the most sensitive measure of resistance in a field strain. The resistance ratio (RR) measured by topical appl ication was 122.6 for cypermethrin at LD50. As measured by surface con tact, the resistance ratio at KT50 was 2.9. Differences between the wa lking movement of cockroaches of susceptible (VPI) and field (RHA) str ains on deposits of cypermethrin influenced KT50 values. A bioassay wi th unrestricted movement resulted in RHA strain cockroaches accumulati ng a larger dose on the tarsal pads and subsequent reduction of the re sistance ratio at KT50. Less walking by the VPI strain resulted in les s insecticide accumulation on their tarsal pads. On a bioassay in whic h movement was restricted, the amount of insecticide accumulating on t he tarsi was equalized, resulting in an increased resistance ratio at KT50. Differences in susceptibility were more accurately measured when the two strains were topically treated (either on the thorax or the t arsal pads) with known doses of insecticide.