Cotton leaves were dipped in serially diluted solutions of formulated insecticides for 10 s with slight agitation. The leaves with second instar nymphs that were dipped in double-distilled water containing 0.1 g L-1 Triton X-100 only, served as control. Each bioassay including control used 3-4 replicates at a minimum of eight different concentrations and were maintained at the controlled growth condition. All the insecticides concentrations were selected to give a range of 0-100% mortality of B. tabaci nymphs. Two weeks later final mortality was assessed when the last nymphal instar had been reached on control plants. It was computed by comparing the number of second instar nymphs present at the time of treatment with the number remaining dead or unhatched on the day of mortality assessment. For bioassays with synergists (PBO and DEF), the cotton leaves containing the second instar nymphs of B. tabaci were dipped into synergist solutions (100 mg L-1) for 10 s at least 2 h before the imposition of insecticide treatments. Other procedures were same to those with insecticides only.