Dickson, R.C. 1941 Inheritance of resistance to hydrocyanic acid fumigation in the California red scale.. Hilgardia 13(9): 515-522.

Notes: Resistance to HCN fumigation in Aonidiella aurantii depends on a single gene (or group of closely linked genes) in the X-chromosome and is therefore sex-linked. Although the red scale was relatively easy to kill by HCN fumigation in the early use of this method of control in California, the red scale population probably contained individuals in which the resistance factor was present. The regular control of red scale by HCN fumigation increased the percentage of resistant individuals in the population because of their preferential survival. With continued fumigation, the red scale will become generally resistant to such control until practically all the population is of the pure resistant strain. Once this condition is reached, there should be no appreciable increase in this resistance.