Field trials were carried out in many different villages, distributed in 10 districts at Kafr El-Sheikh Governorate during three successive seasons (1997, 1998 and 1999) to determine the changes in the population density of the PBW and to evaluate the  relationship between the population density of P. gossypiella male moths, captured in sex pheromone traps (from May 30till September 20^th) and the infestation percentages in green bolls (from July 16 to September 8^th) in the treated and untreated cotton fields. The number of male moths, captured in sex pheromone traps was higher in untreated area than that of treated one during the whole period of investigation. On the other hand, the fluctuations in the population size of moths changed from one time to another forming four clearly intervals periods of activity (four peaks) from late of May to half of September of the three cotton seasons. The percentage of infestation by P.gossypiella in cotton green bolls in untreated area was also higher than that of treated one. The percentages of infestation during 1997 season were generally harboured the highest number, following by that of 1998 and 1999 seasons, respectively, in the treated and untreated areas in the different districts of Kafr El-Sheikh Governorate. The results indicated that there were a strong relationship between the population of  P. gossypiella male moths and the percentage of infestation in cotton green bolls in untreated areas of the 10 districts during the whole periods of study, while insignificant relationship between them was resulted in the treated cotton fields during 1997, 1998 and 1999 cotton seasons.