During the study seasons 2004 and 2005, squash plant leaves were chosen to estimate the infestation of whitefly different stages and virus infection ratio in Dakahlia Governorate. This study was carried out to classify the natural infestation of the whitefly and associated virus infection ratio on squash leaves. The first appearance of the whitefly on summer plantation occurred during the late of April 2004 with low adult number and then gradually increased to reach the highest level of infestation during the mid of July of the same season and during early of August for nymphal stages However, the same trend of population was recorded in 2005 summer season but with different numbers recording the peak of abundance during the last week of August for adult stage and during the early of the same month for nymphal stages population. However, the regular inspection of squash leaves revealed that the early infestation of whitefly on squash leaves during Nili plantation was determined during the late of April 2004 and continuously increased till reaching to their maximum population level during mid of both July and August for adult stages. The population of whitefly nymphal stage was slightly lower than that of adult recording the peak of abundance during early of August. During 2005 Nili cultivation season, the adult and nymphal infestation of whitefly was obviously denoted that the population was in a gradually increased reaching to their highest level during late of August. Moreover, the virus infection ratio in this study during Nili plantation was recorded the highest ratio during early and mid of August 2004 and late of August 2005.The regular inspection of squash plantations during the different sowing times through the experiment revealed that the following periods Summer 2004, summer 2005 and summer 2006 were the preferable time for growing the population of the whitefly nymphs but the Nili 2004 and Nili 2005 were the lowest period for harboring the nymph population. From the obtained results there were very highly significant differences between the time of planting and the infestation of insect nymphal stages. However, the population of the adult stages of whitefly on squash plants in the tested regions was obviously highly than that occurred in nymphal stages. The plants sowing in summer 2005 was the best for growing the adult stages of this insect in comparison with other planting times. Summer 2006 come in the second order followed by summer 2004 but the Nili planting time was represent the least preferable time for increasing the whitefly adult stage on squash. The virus ratio infestation was clearly higher when the plants were sowing during summer 2004 but the least preferring time for growing the virus was obviously observed during the period of Nili 2004.