Insect pest may move to near area to forage the food by adverse changes of their environments. Understanding these behaviors of searching the host will be helpful for further control. This study was performed to investigate the host preference and distribution of B. tabaci in a host plant when they needs. Once entered an area including hosts, B. tabaci will select a host rather than non-host and stayed for living. Dispersal within a niche (in a whole plant), B. tabaci was observed in lower part in tobacco and middle in tomato when seedlings, but they dispersed throughout the whole fully grown tomato plants with irregular inclined to the under, outer stretched leaves. Bemisia tabaci was also caught massively in yellow sticky traps in height of 30 cm above soil, and 30 cm above a plant. There was no attraction effect by flower model traps and fly catcher. When introduced with different densities (0, 10, 50, 100, 200, and 400) in square cages, the B. tabaci do damaged at the densities of 200 with mild and 400 with severe symptom on plants in two weeks and four weeks after inoculation.

Economic injury level was estimated for the sweetpotato whitefly, Bemisia tabaci on greenhouse tomato (Lycopersicon esculantum cultivar pinktop). In the greenhouse, seedling tomato transplanted at mid-April and inoculated B. tabaci at late-April with the densities of 0, 1, 3, 9, 27, 54, 108 and 216 per plant. Only 108 and 216 inoculation densities increased until mid-July. Total weight of fruits was not showed the differences by initial whitefly density; however, the total weight of marketable fruits decreased significantly among plots by higher initial whitefly density. The rates of yield loss increased with increasing whitefly density, resulting in 8.3, 14.0, 29.7, 29.7, 25.7, 40.4, and 69.4% reduction in each of the plots, respectively. The relationship between initial whitefly densities and yield losses was well described by a linear regression, Y= 18.09X+6026.5, R2=0.8504. Based on the relationship, the number of adults per plant which can cause 5% loss of yield was estimated to be approximately 17.