Experiments were carried out to study the population fluctuations of some insects infesting vegetables and field crops trapped by using light traps and the effect of some temperature and relative humidity on these insects during the two years of investigation at Mansoura region. The obtained results revealed that Agrotis spinifera Hbn. recorded six peaks all the year a round. These peaks were found in the 3^rd week of March, in the 4^th week of April, in the 2^nd week of June, in last week of July, in the first week of September, and in the end of October, during the two years of study. Agrotis pronuba Led. and Syngrapha circumfelexa  L. had four peaks per a year during the period of study. The data showed that   Earias insoulana   Boised. had five peaks all the year a round and  Gryllotalpa africana Pal. recorded three peaks per year. Results indicated that the values of correlation coefficient of the relationship between the average temperature, relative humidity and the population fluctuation of these five insect speciesduring the two years of study, cleared that average temperature and relative humidity parameters exerted varied effect with a value ranged from slight to highly significant correlation during the period of study.