Harris Bed Bug Silica powder is part of the Harris Black Label lineup, a line of products designed to kill the toughest pyrethroid resistant bed bugs. If you’ve tried multiple bed bug products with no success, you may be dealing with a tough-to-kill pyrethroid resistant strain, which are prevalent throughout the United States. Whereas diatomaceous earth powder cuts the exoskeleton of the insect causing gradual dehydration, silica powder pulls the moisture out of the insect. Apply in areas where bed bugs have been seen. A very, very light dusting is all that is needed.