Investigation was carried out to survey the main insects attacking the vegetable crops caught by using light traps and the population fluctuations; flight activity of four nuctuids insect species and the effect of weather factors on the population fluctuations of these species during the two years (2016 and 2017) at Mansoura district. Results obtained revealed that there were nine species belonging to Family: Noctuidae (Order Lepidoptera), one species of the Family: Gelechiidae and one species of Family:Pyralidae. One species of Family: Gryllotalpidae (Order Orthoptera) were recorded. Meanwhile, one species of   Family: Pentatomidae (Order Heteroptera) and one species of Family: Scarabaeidae (Order: Coleoptera) were found. Data obtained showed that the population fluctuation of Spodoptera littoralis (Boisd.)  had seven peaks were found all the year round. The results cleared that Spodoptera exigua (Hubner) was recorded five peaks in vegetable crops. These peaks were occurred in the 3^rd week of March, last week of April, 2^nd week of June, 1^st week of Aug. and 3^rd week of September, during the first year of study, In the second years, the peaks were during the 1^st week of Febr, 2^nd week of May, last week of June, 3^rd week of Aug. and 1^st week of Oct. The population fluctuation of Agrotis ipsilon (Hufn.) revealed that this insect had six peaks in vegetable crops. The obtained data cleared that population fulctuation of Heliothes armigera Hbn This insect had four peaks in vegetable crops. These peaks were occurred in the 2^nd week of May, 2^nd week of June, 3^rd week of July and 2^nd week of Sept. during the first year of study. In the second year, the peaks were during the 3^rd week of March, last week of June, 1^st week of Aug. and 1^st week of Sept. Results indicated that the values of correlation coefficient of the relationship between the average temperature, relative humidity and the population fluctuation of these four insect speciesduring the two seasons of study, assuted that the average temperature and relative humidity parameters exerted varied effect with a value ranged from slight to highly significant correlation during the two seasons of the investigation.