The same numbers of Bemisia tabaci (Gennadius) biotype B and Q adults were released on tomato plants grown in soil treated with different insecticides at planting. Around 60–160 days after the release, the growth response and competitive displacement of biotype B to Q were monitored at two different periods (the summer and winter periods). Compared with the control, the numbers of adults were lesser at the insecticide treated plots. Although the ratio of biotype B decreased at the imidacloprid-treated plot, it increased at the chlorantraniliprole-treated plot and control plot. These tendencies did not change between the two periods. These results indicate that the displacement of biotype B to Q (or Q to B) would strongly depend on whether the insecticide treatments are lesser effective on one biotype than the other.