The insecticides resistance of German cockroach Blattella germanica L. and the role of mixed function Oxidase in insecticides resistance.

The sensitivity of a field strain (HZ) of the German cockroach , Blattella germanica L. to per- methrin, deltamethrin and cypermethrin was tested using a topical application method to estimate LD50. The results indicate a high level of resistance in this strain to pyrethroids, especially to permethrin. The LD50 resistance ratios (RR) for permethrin , deltamethrin and cypermethrin were 67.1 , 18. 1and 11. 8 , re- spectively. Studies were conducted (in vivo) on the HZ strain to determine the synergistic effect on perme- thrin by metabolic inhibitor piperonyl butoxide(PBO). The synergistic effect on the Ld50 RR for PBO was 3. 69 times, which indicated that the mechanism for pyrethroid resistance in the HZ strain was associated with mixed function oxidases (MFOs).Biochemical analysis showed that MFOs activities in the resistant (field) strains were higher than those in the susceptible strain. These data indicate that the difference in the activity of MFOs are important factors in the development of insecticide resistance in the field strain of German cockroach evaluated.