中文摘要：

家蝇是重要的卫生害虫，拟除虫菊酯杀虫剂的广泛使用导致了家蝇抗药性的产生，家蝇种群演化出了多重的抗性等位基因。为推测抗性等位基因在无杀虫剂选择压下是否存在适合度代价，对来源于野外的北京家蝇种群（ BJ2010）连续饲养25代，在不接触杀虫剂的实验室条件下，每隔5代检测基因型频率，测定该种群的钠离子通道等位基因和CYP6D1基因频率随时间的变化。研究结果显示，与拟除虫菊酯抗性相关的钠离子通道抗性等位基因kdr-his和CYP6D1v1频率值随时间有一定的波动，但没有显著的变化，说明kdr-his和CYP6D1v1等位基因在无杀虫剂选择压下不存在明显的适合度代价。另一钠离子通道抗性等位基因kdr起始频率很低，其频率的最终减低可能是由于遗传漂变的结果。因此，伴随拟除虫菊酯杀虫抗药性出现的抗性等位基因在BJ2010品系家蝇中并不表现适合度劣势，提示家蝇对拟除虫菊酯类杀虫剂的抗性一旦形成，将难于自然消减。

英文摘要：

The house fly （ Musca domestica） is an important veterinary and medical pest.The intensive use of pyrethroids against house flies has lead to the development and spread of pyrethroid resistance .Multiple resistance alleles of the voltage sensitive sodium channel gene （e.g.kdr and kdr-his） and cytochrome P450 （e.g.CYP6D1） have evolved in populations of the house fly worldwide.It has been predicted that the appearance of a resistance allele often has a fitness cost in the absence of insecticide selection under field conditions, however, empirical evidence is very limited.In this study, we attempted to investigate the possible fitness costs for pyrethroid resistance alleles by monitoring their frequencies in a field-derived Beijing house fly population under insecticide-free laboratory conditions over 25 generations.Our data show that frequency declination was only observed in the kdr allele that had a very low initial frequency, whereas no change was evident in the frequencies of kdr-his and CYP6D1v1.These results imply that there are no fitness costs for the CYP6D1v1 and kdr-his alleles.