| pubmed-article:2367264 | pubmed:abstractText | Resistance to pyrethrins plus piperonyl butoxide (PB) in a population of Fannia canicularis (L.) (BR strain) at a broiler-breeder facility was determined (in F2 laboratory generation) to be 109.1-fold the median lethal dose (LD50), apparently having been influenced by twice-daily treatments with automatic spray equipment during the previous 2 years. By contrast, resistance was only 12-fold the normal LD50 in a population of Musca domestica L. (DH strain) at an egg-production facility that was subjected during a comparable period to treatments twice per week with synergized pyrethrins with the identical automatic pyrethrin-spray system. The automated application of a nonpersistent chemical at frequent intervals, obviously, provides continuity of selection pressure leading to high levels of resistance. Other factors such as enclosed poultry housing and the elimination of refugia have also contributed to the enhancement of resistance. The resistance level in Strain BR regressed to 31.7-fold after remaining unselected for an additional generation in the laboratory. Other bioassays on the F2 generation revealed limited resistance toward permethrin of 3.7-fold the normal LD50. | lld:pubmed |
