An accurate estimate of a population is essential for pest management. For Frankliniella occidentalis (Pergande) in strawberry, counts of thrips in flowers are commonly used as there is a strong correlation between thrips number per flower and fruit damage. The aim of this study was to look at the abundance and population structure of thrips within different flower stages and positions on the plant to test whether these affect population estimates. Adult females were found in open buds (petals showing), but were most frequent in young and mature flowers, whereas adult males were not found in buds and were most frequent in mature and senescent flowers. Twice as many adult thrips were found in mature flowers at the top of the plant compared to those at the side. Only larvae were found in closed buds (no petals showing). Larval numbers increased gradually with flower stage and peaked in senescent flowers. Numbers of adults and larvae declined after flowering. Total numbers of thrips and the ratios of females:males and of adults:larvae varied systematically with flower stage. The choice of flower stage and position for sampling could affect population estimates by as much as a factor of four.