Western flower thrips (WFT), Frankliniella Occidentalis (Pergande), feeding on cotton seedlings (Gossypium hirsutum L., var. Acala SJ-2) grown in growth chambers for 8 weeks caused significant reductions in plant root development, leaf area, and final plant dry matter of both above and below ground biomass when compared with plants protected by a systemic insecticide. Field trials showed similar reductions in early season total plant biomass and harvested lint yields from early thrips damage.