This investigation was carried out to study the effect of some chemical constituents (total phenols, total carbohydrates, total proteins and pH values) of three citrus tree host leaves (sweet orange, navel orange and mandarin) on the population density of Aonidiella aurantii (Maskell)and Chrysomphalus aonidum (L.) in relation with prevailing temperature and relative humidity in different citrus orchards at Minia Alkamh district, Sharkia Governorate, Egypt during two successive years extended from December 2012 to November 2014. The results showed that sweet orange appeared to be the most susceptible citrus tree hosts to infestation by the scale insects followed by navel orange and mandarin at the least. The population density of A. aurantii had three peaks on the three citrus tree hosts in the two years. Also, C. aonidum recorded three peaks on the navel orange in the two years, while on sweet orange indicated four peaks occurred during the first year and three peaks of densities were obtained during the second one. On mandarin trees, three and four peaks were observed in the aforementioned years, respectively. The highest population was exhibited by A.aurantii in the first peak by 636 insects/300 leaves on sweet orange on February in the second year while, it was recorded by C. aonidum in the third peak by 59 insects/300 leaves on October in the same year. There was a positive relationship between both of total carbohydrates and total proteins and the population density of A. aurantii and C. aonidum on sweet orange, navel orange and mandarin, while no relation was found between each of total phenols and pH values and the infestation level by the two scale insects.