Cameron, J.W., Carman, G.E., & Soost, R.K. 1969 Differential resistance of Citrus species hybrids to infestation by the California red scale, Aonidiella aurantii (Mask.).. Journal of the American Society for Horticultural Science 94(6): 694-696.

Notes: Populations of Citrus hybrids involving 5 species, including parental inheritance from mandarin, orange, grapefruit, pummelo, and lemon, were studied for degree of natural infestation by the California red scale over the periods 1948-58 and 1963-68. During the first period, 1884 hybrids showed wide variation in infestation within and among parentage groups, but there was evidence that mandarin ancestry contributed resistance while pummelo and lemon ancestry contributed susceptibility. In 1960, 81 apparently resistant hybrids from several parentage groups, and a control group of lemons, were repropagated in a randomized field plot. Scale ratings for 6 years indicate that there is inherited resistance dependent upon ancestry, in the order: mandarin parentage, greatest; mandarin-orange and mandarin-grapefruit, second; pummelo-orange and pummelo-grapefruit, third; lemon, least. These data are in agreement with earlier indications that varieties of the mandarin are relatively resistant to California red scale, while the pummelo and especially the lemon are more favorable hosts.