Field experiments were carried out at Sakha Agricultural Research Station, Kafr El-Sheikh governorate during 2013/14, 2014/15 and 2015/16 seasons, to study host preference and the population densities of Thrips tabaci Lind. andMonacha spp. in lettuce (Roman), onion (Giza red) and garlic (sids 40 and balady cultivars)  plantations. Also, the relationship between the biochemical leaf components (Chlorophyll, moisture, potassium (K), nitrogen (N) and phosphorus (P), protein, total carbohydrates mg/kg and phenols) and pest population density. The population density of T. tabaciwere detected in lettuce, onion, garlic (sids 40 and balady) plantations by late January. The population density of T. tabaci progressively increased to reached its peaks during February and March. No land snails were detected on balady garlic. Snail populations in lettuce, onion, garlic (sids 40), were low or moderate until  mid February, and then gradually increased to maximal peaks in February and March. The highest population density of thrips was observed in onion followed by garlic when compared with lettuce, while Monacha spp. was opposite.  Garlic (sids 40) had higher chlorophyll content followed by balady garlic than lettuce. Almost, K, N, P, protein, total carbohydrates and total phenols significantly varied among vegetable crops (p≤ 0.05). In addition, there is a positive correlation between the population density of T. tabaci with each of chlorophyll content, moisture, P and total phenols, while relationship between the population density and K, N, protein and total carbohydrates were negative. There is a negative correlation between land snails and chlorophyll content but it was positive with each of moisture, N, protein and total phenols and positive significant with K (p≤ 0.05).