House flies have evolved resistance to most insecticides, and as insecticide use continues over seasons it is expected that levels of resistance will rise. Freeman et al. recently investigated (https://www.sciencedirect.com/science/article/pii/S0048357519301282?via%3Dihub) flies collected from livestock facilities in five states to check levels of resistance against three commonly used insecticides. A population collected from Kansas had previously unseen high levels of resistance to permethrin, a pyrethroid insecticide, that could mean this type of insecticide will be of limited use for house fly control in the United States in the near future.
