The effect of natural conditions on some biological aspects of the parasitoid Trichogramma evanescens (Westwood) was studied when reared on Sitotroga cerealella eggs in the laboratory and attacked both Pectinophora gossypiella (Sound.) and Sitotroga cerealella, (Oliv.) eggs in natural conditions.  The study was conducted on three ages of the parasitoid i.e., 3, 5 and 7 day's old after parasitism on temperature degree of 25°C±1 and 75±5%RH. The investigation was carried out by conducting two experiments; the first was under incubated conditions, 25°C±1 and relative humidity 75±5%. The second was under normal weather conditions during June and July2013 in open area in plant protection research institute. Results showed that every age was affected by exposure to natural conditions comparing with incubated one. The total mean percentage of adult emergence decreased from 96.34% in incubated conditions to 93% in natural conditions. The percentage of emergence for the parasitoid of 5 days age did not affect by exposing to natural conditions, as the percentages were insignificantly differed from 95.67 to 94.13 % for incubated and natural conditions, respectively. The age of 3 days old was the most affected age by exposure to natural conditions. General productivity of the parasitoid was higher when attacked P. gossypiella eggs (20.98♀/female) than when attacked S. cerealella eggs (13.90♀/female) in natural conditions.