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A field survey was conducted in the summer of 2003 and 2004 to evaluate resistance to deltamethrin on house flies, Musca domestica, from 17 urban garbage dumps in the cities of Beijing, Tianjin, and Zhangjiakou. Bioassays were carried out by topical application with technical deltamethrin to measure the levels of resistance to deltamethrin. Tests for synergism with piperonyl butoxide (PBO) were used to study the occurrence of metabolic resistance mechanisms. Competitive polymerase chain reaction (PCR) amplification of specific allele (cPASA) assay was used on individual house flies from these field populations to detect the presence of the kdr and super-kdr alleles associated with pyrethroid resistance. Another PCR followed by labeled allele-specific oligonucleotide hybridization (PCR-ASO) confirmed the presence of the mutation and hence checked the accuracy of cPASA. Deviation of genotype ratios from Hardy-Weinberg equilibrium was tested. Relative to a susceptible laboratory strain, field house ...