Pyrethroid-Resistance Mechanism in German Cockroach, Blattella germanica (Orthoptera:Blattellidae)

German cockroaches, Blattella germanica, were collected from the field (O-colony) and their susceptibility to 12 insecticides was determined by a topical application. This population exhibited resistance to all pyrethroid compunds tested and to DDT, but not to fenitorothion, diazinon, propoxur and methoxadiazon. Piperonyl butoxide, an oxidase inhibitor, had no synergistic activity with permethrin against the O-colony. However, NIA 16388, which can act as both an oxidase and esterase inhibitor, exhibited the synergistic effect with permethrin. Electrophysiological study suggested that nervous system insensitivity (kdr-factor) might be involved in this colony. The nervous system of this coloby was also insensitive to aconitine which blocks the inactivation of sodium channels, so it was assumed that the nerve insensitivity could be due to modification in the sodium channels. These results suggested that the increase of esterase activity and insensitivity of the nervous system contribute to pyrethroid resistance in this insect.