Michelbacher, A.E. 1957 Frosted scale on walnuts in northern California.. The Pan-Pacific Entomologist 31(3): 139-148.

Notes: Lecanium pruinosum occurs in most of the walnut orchards in northern California. This pest is attacked by Metaphycus californicus, among other parasites, and was usually kept under control. Where high dosages of DDT are used to control the codling moth, serious infestations of the frosted scale frequently develop. Other treatments are investigated.