The red scale, Aonidiella aurantii (Mask.), was first noted in California in 1877. Two years later, introduction of its natural enemies was first suggested, and since 1891 nearly all the citrus-growing regions of the world have been searched for parasites or predators that would control it. At various times and in various countries claims have been made that parasites or predators or a combination of the two controlled red scale. True, there are countries, particularly China, where red scale seldom injures citrus seriously, or even rarely infests this host. This has been attributed sometimes to one, sometimes to another, or to a combination, of its insect enemies; but the evidence is not sufficiently convincing that its innocuousness in such regions is due solely to these enemies. All the factors need to be weighed, especially host-plant relations of red scale, which are complex and often contradictory from one country to another. The red scale is not a serious citrus pest in Florida, where insect enemies are not considered to be a factor, except by the most partisan adherents of biological control.
