The purple scale, Lepidsaphes beckii (Newman), California red scale, Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) and the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) are of the most important and serious pests infesting citrus orchards. The present study was carried out during the period from the 2nd of June till the 17th of November 2021 in an orchard cultivated navel orange, mandarin and lemon located in the Experimental Farm of Faculty of Agriculture, Mansoura University, Egypt to study some ecological aspects of the tested pests. The obtained data showed that L. beckii and P. citrella preferred navel orange followed by lemon and mandarin; while, A. aurantii was recorded on lemon leaves only. L. beckii showed two peaks of activity in navel orange and one peak in mandarin and lemon orchards; also, A. aurantii showed only one peak of activity in lemon orchard. P. citrella showed three, one and two peaks in navel orange lemon and mandarin orchards, respectively. The diaspidids L. beckii and A. aurantii in lemon and mandarin trees preferred east direction followed by north; while, on navel orange trees, L. beckii was higher in middle followed by west direction. Also, P. citrella preferred middle and east direction of its host trees. Statistical analysis showed that temperature degrees had a positively significant effect on L. beckii population (especially in navel orange orchard); while, this effect was insignificant on A. aurantii population. In contrary, P. citrella population showed negative response to the increase of temperature degrees and showed mostly positive responses to the increase of relative humidity during the present study. Chemical analysis showed that navel orange leaves had relatively high content percentages of nitrogen and carbohydrates coincided with the low content of humidity.