The laboratory began the rearing of Macrocentrus ancylivorus in 1942–1943 on green apple slices as host food, and in the following year 54,000 were produced, of which 26,000 were liberated in the field against the first generation of the Oriental fruit moth. In 1943, it was found that Macrocentrus could be reared by using the potato tuber moth as host insect and potatoes as host food, and this method has since been continued. For a period of three years most of the parasites reared by the laboratory were turned over to B. F. Driggers of the Experiment Station for liberation against first and second brood peach moths in order to compare the efficiency of such liberations. At one time it was hoped that enough parasites could be produced to supply the demands of New Jersey peach growers, but rearing difficulties plus limited laboratory facilities prevented this. Trouble with a parasitic disease of the host insect was encountered in 1944–1945 and has continued to hamper production. However, 155,000 were reared and released for experimental use. With the advent of DDT rearing was discontinued.