Development of a Strain of Houseflies Resistant to DDT

Abstract

About 300 houseflies were exposed to a DDT fine-mist spray in a 100-cu. ft. chamber. One ml. of a 1% DDT-kerosene spray was discharged into the chamber and the flies were exposed for 2 min. About 10% survived, and these were used as parent stock for a new special colony. Each of 14 generations was similarly exposed to DDT, and the survivors allowed to propagate. After the 3d generation, 4-day-old flies from the regular colony and the special stock were exposed to the mist spray at the same time. The survival of the special flies was greater than that of the flies from the regular stock. An increased quantity of DDT was needed to kill the special flies. In tests with the 14th generation, the av. mortality with 1600 4- and 5-day-old flies was 69% for the regular stock and 34% for the special flies. Selective breeding produced a strain that was more resistant to DDT than were flies from the regular stock.