Solenopsis mealybug establishment onto cotton and the damage they inflicted at different plant development stages was studied in a glasshouse trial and through field observations. The plant growth stages that were studied included; 4-5 leaf, squaring, early boll, late boll and mature. Results from these studies indicate that the earlier mealybug establish on cotton, the more damage they cause. Solenopsis mealybug establishment at 4-5 leaf stage caused 100% yield loss while infestation at squaring and early boll stage caused 90 and 65% yield loss respectively when compared to the control plants with no mealybug. Establishment of solenopsis mealybug on mature plants caused little or no yield loss.