Experimental trials were conducted on four different vegetable Solanaceae crops; namely tomato, white eggplant, spicy pepper and potato throughout 2013 early summer growing season at the Agricultural Research Center Experimental Station (Qaha), Qalyoubia Governorate, Egypt. Results revealed that the combined effect of the three weather factors (i.e. maximum and minimum temperatures and relative humidity) did not fully explained the variance in the population density over time. Explained variance (EV) was 19.98, 62.23, 60.62 and 59.7 % for tomato, eggplant, pepper and potato plants, respectively. Considering plant phenology as plant age (X) (presented by three degree polynomial equation, Y= a + b₁X+ b₂X²+ b₃X³) revealed the most relation to the variance in population. EV was 49.67, 90.58, 76 and 84.22% for tested plants, respectively. The added effect of weather factors to the plant age revealed EV as 74.32, 92.24, 83.45 and 94.02% for tomato, eggplant, pepper and potato plants, respectively. These added values did not seem to be significant. These results do not eliminate the effect of weather factors on the population dynamics. Under laboratory conditions; these factors may reveal a great deal of effect. Under field conditions these factors firstly affect the plant growth which makes the plant more palatable for infestation. So plant phenology as plant age took over the effect of weather factors mathematically.