[Objectives]  Infection of the whitefly, Bemisia tabaci (Gennadius) by facultative symbionts varies with host plant and some facultative symbionts can cause feminization of the host. Studies of the relationship between facultative symbiont infection and sex ratio in field populations of B. tabaci will be helpful to understand the breakout mechanism of this insect pest. [Methods]  B. tabaci adults were collected from field populations from four species of host plants in Nanjing, China, and their sex ratios and frequency of symbiont infection determined. [Results]  Hamiltonella defensa and Rickettsia infection in B. tabaci varied with host plant, including cotton, tomato, cucumber and sweet potato. Hamiltonella was the most common symbiont on all host plants, and frequency of infection of this symbiont was highest on cotton, followed, in descending order, by cucumber, tomato, and sweet potato. The frequency of Wolbachia and Cardinium infection was not affected by host plant. Females comprised > 60% of all four B. tabaci populations and there was no significant difference in the proportion of females among different host plants. Regression analysis indicates that both Hamiltonella and Rickettsia infection are related to a female biased sex ratio, and quadratic polynomial regression models established an association between infection frequency and female ratio. When the infection rates of Hamiltonella and Rickettsia were lower than 69% and 5%, respectively, the proportion of females increased with infection rate. However, when symbiont infection rates were higher than those above, female ratios decreased with infection rates. [Conclusion]  B. tabaci populations on cotton, tomato, cucumber and sweet potato are all female-biased, and sex ratios are not significantly different among different host plants. The infection frequencies of facultative symbionts is related to the population sex ratio.