Toxicological analysis
The responses of house flies from different populations to permethrin
with or without PBO were used for identification of
P450-mediated resistance [25]. According to the LD50 result of bioassay
(Table 2), BJD strain exhibited high levels of resistance to
permethrin (2534-fold), compared with susceptible TJS strain
(5-fold). Among the detected five field population house flies,
Guangdong population displayed the highest resistance ratio to
permethrin (364-fold), followed by Shanghai and Shandong (256-
fold), Beijing (177-fold) and Jilin population (95-fold).
PBO, the P450 inhibitor, increased permethrin toxicity to different
extents in all house fly populations. When the house flies of BJD
strain were pretreated with PBO, the resistance ratio was reduced
from 2534- to 119-fold. PBO also reduced the expression of permethrin
resistance in the five field populations, reducing the resistance
ratios by 15- (Jilin population) to 109-fold (Shanghai
population) with 2- to 6-fold permethrin resistance remaining.
These results suggest that P450s-mediated detoxification has an
important role in pyrethroid resistance in these house fly
populations.