The present study was carried out to investigate the simultane­ous effect of certain environmental physical factors on the population activity of pink and spiny bollworms during 1993, 1994 and 1995 sea­sons in three different localities (Gharbia & Kafr El-Sheikh and Beheira Governorates). The relationship between accumulative thermal units and the corresponding population density of the pink bollworm was studied. The effect of maximum and minimum temperature and relative humidity on the population density of Pectinophora gossypiella (Saunders) and Earias insulana (Boisd.) moths was also investigated. It appears from the results that a strong positive relationship prevailed between the changes in the population density of each generation and the required accumula­tive thermal units for the three years combined in the three tested local­ities. The effect of the three weather factors combined was relatively the highest for Gharbia, while the corresponding population size of 59W was on contrary the least. A similar trend could still be observed for 1)9W.