Effect of Method of Application on Resistance to Pyrethroid Insecticides in Blattella germanica (Orthoptera: Blattellidae)

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Abstract
A DDT-resistant ( kdr ) strain of Blattella germanica (L.) (VPIDLS) showed broad cross-resistance to all pyrethroids when tested by topical application to the abdomen. By contrast, the strain’s cross-resistance spectrum did not extend to cypermethrin and deltamethrin (two typical Type II pyrethroids) when a surface contact method was used. To understand the cause(s) for such a difference in cross-resistance expression, different application methods and toxicity criteria were examined. Location of topical application, including the head and tibia, had little influence on the cross-resistance pattern. We concluded that, by surface contact, cypermethrin and deltamethrin act in a way atypical of DDT or other typical Type I pyrethroids.