This study was carried out at Mallawi region ,  Minia, Governorate during three successive seasons of cotton  (2004, 2005 and 2006) to evaluate the efficiency of releasing distances , numbers of releasing times of the egg- parasitoid , Trichogramma evanescens West. and further  to determine the effect of such parasitoid; alone or with Agerin, (a local commercial product of Bacillus thuringiensis ) as  a biological control compared with recommended insecticides (Nastiban ,Tetition and Kendo) against the bollworms Pectinophora gossypiella and Earias insulana infesting cotton fields.Besides, effects of different treatments on seed cotton yield and some yield components were also studied.Results could be concluded as follows : The efficiency of the egg- parasitoid , T. evanescens releasing process was gradually enhanced with decreasing  the distance between the wasp release point, but with increasing  number of applications. The lowest cotton boll damage caused by the bollworm larvae and highest  cotton productivity were obtained from cotton fields 10 m away between releasing points with no significant differences between 10 and 15 m releasing distances .The higher number of Trichogramma application (five times) gave the lowest mean number of bollworm larvae (2.5 and 2.8) associated with the highest number of open bolls/plant (11.1 and 9.8),boll weight(2.92 and 2.89) and seed cotton yield (8.0 and 6.8 kent./fed.) in both season, respectively.  Results showed that the biological control by egg- parasitoid, T. evanescens alone or with Agerin (B.t.) was more efficient than chemical control in reducing boll worms damage and in improving cotton yield under both early and late planting dates. Early planting of cotton fields gave lower bollworm infestation and higher yield and yield components in all control treatments as compared with late planting in both seasons. The maximum reduction in bollworm and the highest seed cotton yield and yield components were produced by the combination application of Trichogramma parasite and Agerin (B.t) followed by Trichogramma alone. In addition, biological control against bollworm increased number of five predaceous insects in released cotton as compared with chemical control in both seasons. The highest number of predators was recorded in fields treated with Trichogramma parasite and Agerin ( B.t.). together (52.6 , 72.6) , followed by those released  with Trichogramma parasite alone (46.4 , 63.6), treated areas with recommended insecticides were the least ( 31.7 , 33.8 )  in both seasons, respectively Furthermore, biological control reduced the costs of cotton protection. The costs of  protection per feddan were dropped by  60.15 % and  27.10 %  for the utilization of Trichogramma parasite and  with Agerin (B.t.) compared with the chemical treatments.  It could be concluded that the biological control program including five applications of the Trichogramma parasite and two sprays of Agerin (B.t.) achieved the highest rate of reduction in infestation cotton bollworms, increasing predaceous insects associated with bollworms, improving cotton productivity, decreasing the costs of cotton protection process and avoiding environmental pollution at the same time.