The inter-relationship between population density of both Lea­caspis riccae Targ. (Homoptera, Diaspididae) and Patella unionalis Hb. (Lepidoptera, Eyraustidae) on olive trees in El- Fayoum Governorate and three climatic factors (temperature, R.H. % and sunshine periods) was studied during the two consecutive years of 1999 and 2000. It was found that the population of L. riccae had 4 peaks and insignificantly cor­related with the three tested environmental factors during the two years of investigation. Whereas, R.H. % significantly affected the population fluctuations of larvae of P. unionalis that had 2 and 3 peaks during 1999 and 2000, respectively. The highest mean numbers of larvae were re­corded during spring months, whereas the lowest ones were recorded during summer season throughout the two years of investigation.