Effects of the Food Plant of California Red Scale, Aonidiella aurantii (Mask.) on Reproduction of its Hymenopterous Parasites

Discrepancies in the degree of biological control of insect pests where the food plant species of the host were the only known variants in the environment have been subjects of scattered observations in the literature by Morgan (1910), Compere (1936), Gilmore (I938), and others. A long period of speculation on the existence of strains of California red scale, Aonidiella aurantii (Mask.) immune to attack by parasites culminated in the discovery by Flanders (1939a, 1942a) that the hymenopterous parasite Habrolepis rouxi comp. reproduced satisfactorily on A. aurantii on Citrus spp. but that verv few emerged from the same species of scale on sago palm, Cycas revoluta Thunb. This was considered to be the reason for Compere's early failure to bring the hymenopterous parasite, Comperiella bifasciata How, from the Orient to California on scale-infested sago palm; Smith (1942) concluded: “Recognition must be given to the possibility that the host plant may confer on the host insect a kind of immunity to parasitization”.