The United States eliminated screwworm in the 20th century by flying planes over hotspots to drop boxes packed with sterile flies. Sterile flies reduce the mating population of the wild flies. The USDA has also invested in a sterile fly production plant in Mexico that is slated to open next year. In Panama, a facility breeds up to 100 million sterile flies per week. The USDA estimated 500 million flies must be released weekly to push screwworm back south in Latin America.