Pyridaphenthion, a new organophosphorus insecticide, was evaluated against three species of insect pests of public health importance. Pyridaphenthion was proved to be as effective as other common organophosphates against house flies, common mosquitoes and German cockroaches, showing somewhat slow-acting but fairly long residual effect. The half effective life of Pyridaphenthion was 100 days on a filter paper, 20 days in an artificial sewage water, and 35 days in diionized water. When the chemical in air was collected and analized by gaschromatography in the progressing time after the residual spraying to the wall in a greenhouse, the concentration showed 146μg/m^3,highest, just after spraying, but rapidly decreased to 13μg/m^3 at 24 hours.
