Abstract: Bemisia tabaci is a major agricultural pest. To reduce the application of chemical pesticides, it is important to take ecological controlling measures for cultivation management. Here, we investigated five agronomic traits of tomato seedlings and Q-type B. tabaci population for nine times in greenhouses. Our aim was to probe into the relationship of B. tabaci population density from tomato seedlings and nitrogen levels (i.e., 1134 mg·L^-1, high; 945 mg·L^-1, standard; 756 mg·L^-1, low) by using principal component analysis, linear regression analysis, and Pearson correlation analysis. The results showed that the five traits including plant height, stem diameter, leaf area, chlorophyll relative content, and leaf total nitrogen content followed a similar trend with the order of high nitrogen level > standard nitrogen level > low nitrogen level. The population density of B. tabaci from tomato seedlings at the peak stage for nine times showed the same order of high nitrogen level > standard nitrogen level > low nitrogen level. The results of linear regression analysis and Pearson correlation analysis showed a high correlation between B. tabaci population density and the chlorophyll relative content and leaf total nitrogen content. The results of principal component analysis showed that leaf chlorophyll relative content was the key factor driving B. tabaci population density across nitrogen levels. It was suggested that nitrogen level was one of key factors affecting the growth of tomato and B. tabaci population density: the higher nitrogen level, the better growth of tomato seedlings and the greater density of B. tabaci. Leaf total nitrogen content and chlorophyll relative content were suggested to be the ecological control index to monitor the fluctuation of Q-type B. tabaci population density.

Key words: inorganic phosphorus, Chrysosporum ovalisporum, dissolved organic phosphorus, alkaline phosphatase