Phenothiazine was introduced by DuPont as an insecticide in 1935.[11] About 3,500,000 pounds were sold in the US in 1944.[12] However, because it was degraded by sunlight and air, it was difficult to determine how much to use in the field, and its use waned in the 1940s with the arrival of new pesticides like DDT that were more durable.[13]:161–162 As of July 2015 it is not registered for pesticide use in the US, Europe,[14] or Australia.[15]