The insidious flower bug, Orius insidiosus (Say), is reported to effectively suppress Frankliniella species thrips populations. The objective of this study was to determine the effectiveness of this predator in reducing thrips populations in cotton (Gossypium hirsutum L.). Population fluctuations of the predator and thrips on the leaves, squares, and flowers were tracked on plots in Quincy and Marianna, FL, in 2006 and 2007, and weekly predator-to-prey ratios were used to assess the effectiveness of the predator in regulating the thrips populations. The bulk (> 95%) of the Frankliniella thrips were found in flowers and F. tritici (Fitch) constituted > 98% of the adult thrips population. Other thrips recorded were F. occidentalis (Pergande) and F. bispinosa (Morgan). The highest and lowest weekly predator-prey ratios in the flowers in Quincy were 1:5 and 1:1170, and 1:92 and 1:1900 in Marianna. No correlation was observed between O. insidiosus and thrips abundance. Results of this study indicate that O. insidiosus may not be an effective predator of F. tritici in field cotton during the reproductive stage.