The current field experiments were conducted at Qalyubyia dis­trict for three successive cotton-growing seasons (1996.1998) to in­vestigate the changes in the seasonal activity of the spiny bollworm, Ear­ias insulana (Boisd.). The actual and expected numbers of field generations based upon both accumulated heat units (590 DDs) and zero of development (13.1°C) were estimated. Results showed that E. insulana moths underwent five overlapping field generations during each of the three tested cotton-growing sea­sons. The durations of these generations were as follows: 1^st 10-11 weeks; ed 9-10 weeks; 3^cd and 4^1h 8-9 weeks and 5^1h 8-10 weeks. On the other hand, prediction of this pest from April to next April reveals the presence of five generations on cotton plants. The duration of gen­erations 1-3 (shortest) ranged from 40-48 days in 1996, 40-42 days in 1997 and 36-51 days in 1998, respectively. The last generation was the longest; being 157, 177 and 133 days in the three years, respectively.