Harris Pyrethroid-Resistant Bed Bug Aerosol Spray is the most effective at killing bed bugs of all types and their eggs. There are small pockets of pyrethroid resistant strains of bed bugs in located in some cities in the US. For those strains, tough pyrethroid resistant insecticides are needed to effectively eliminate the bed bug colony. We recommend using this product indoors with a combination with bed bug aerosol and diatomaceous earth powder. Always follow label directions and keep out of reach of children.