The response of the fourth instar larvae of Culex pipiens to three photosensitizing dyes (Rose Bengal,
phloxine B and rhodamine B) was investigated under laboratory conditions. The mortality percentages
increased as the concentrations and exposure times of all tested dyes increased. As judged by a comparison
of median lethal concentration values, Rose Bengal was the most effective dye followed by phloxine B,
then rhodamine B. Treatment fourth instar larvae with different concentrations of three tested dyes induced
morphological changes and aberrations in larval stage. In the current study, based on median lethal time
values, Rose Bengal had the lowest time values and fastest action compared to other tested dyes. Results
also revealed that the addition of non- toxic concentrations of both tween 20 and tween 60 to median lethal
concentration of Rose Bengal showed no significant changes and didn't appear synergism to their efficacies
compared to Rose Bengal used alone.